According to the latter conception, vital activities of cell protoplasm may

be due to changes in water content, to electrical disturbances, to the

phenomena resulting from the conditions brought about by surface boundaries

between the different phases of the gel, to varying osmotic pressure, to

changes in chemical reaction, etc., and may be controlled by various

stimuli of chemical, physical, or mechanical nature. This conception seems,

therefore, to fit most closely the actual conditions under which the

protoplasm exists and carries on its vital functions.

With this conception in mind, we may now proceed to a consideration of how

the various components of the complex organic colloidal system, and their

specific properties, can affect its chemical activities.

The components of the system are, of course, water, salts, and the various

organic compounds (fats, proteins, carbohydrates, and enzymes in all cells;

and other groups, such as essential oils, tannins, pigments, etc., in cells

which have certain special functions to perform) which constitute the solid

phase of the colloidal mixture. In addition to the definite chemical

properties of each of these component groups, which have been studied in

detail in preceding chapters, there are many physical, or

physical-chemical, properties of the system as a whole, and of its

component parts, which are of the utmost importance in the physiological

activities of the protoplasm. These we may now proceed to consider in some

detail.

WATER

Water constitutes the largest proportion of the weight of active

protoplasm. In living cell contents (except those of such bodies as resting

seeds, etc.), water comprises from 70 to 95 per cent of the total weight of

the substance; the average proportion being usually between 85 and 90 per

cent. The fact that protoplasmic material can exist in turgid form with

such high percentages of water as these is due, as has been pointed out, to

its existence as a colloidal gel. It is because of this condition that

increases in the proportion of water generally increase the turgidity, or

turgor, of the protoplasm; instead of, as in all other cases, rendering the

mixture less solid and more labile. Losses of water from the protoplasmic

gel decrease its "swollen" condition and so render the tissue soft and

flabby; while increases in water content swell the gel and make the tissue

stiff and turgid. No other condition than that of a colloidal gel could

respond in this way to changes in water content.

The formula which is commonly assigned to water is the simplest possible

one; namely, H_{2}O. But if the water were really as simple as this, the

compound would boil at a very low temperature, would have a very low

surface tension, etc.; whereas its actual boiling point, surface tension,

etc., are much higher than those of other compounds having a higher

molecular weight than is indicated by the formula H_{2}O. Actual

measurements of the physical properties of water indicate that at the

temperature at which water is a vapor its formula is at least (H_{2}O)_{2};

while at lower temperatures, at which it exists as a liquid, its formula

may be (H_{2}O)_{3}, or (H_{2}O)_{4}, or even more complex still. The cause

for this association of the compound into multiple molecules undoubtedly

lies in the extra valences of the oxygen. In many organic compounds oxygen

is undoubtedly tetravalent, and it may be easily conceived that in these

complex molecular groupings in the water it exhibits this same property;

the possible molecular arrangements being represented by the formulas

H H

H H \ /

\ / H-O-O-H

O=O and | | etc.

/ \ H-O-O-H

H H / \

H H

Such molecules may be conceived to break down very easily, leaving the

extra valences of the oxygen available to form linkages with other atoms or

molecules. This may constitute one of the ways in which water exerts its

remarkable effects both as a solvent and as an accelerator of all kinds of

chemical reactions. Other organic compounds which contain tetravalent

oxygen are exceedingly active chemically, and there seems to be much to

commend this view of the chemical structure of the water molecule.

Probably the most remarkable property of water is its power of solution. No

other liquid surpasses water as a solvent. This power, as has been pointed

out, is supposed to be due to, or in some way correlated with, the extra

valences of the oxygen atoms, which may perhaps unite with similar extra

valences of other substances with which the water is brought into contact,

and so cause the latter to enter into solution. All kinds of substances

dissolve in water, and when in solution, or even when only moistened, are

much more active chemically than when dry. This property of water

contributes greatly to the possibilities of the chemical reactions which

constitute life processes.

Water, likewise, has a higher dielectric constant than any other common

liquid. This means that it does not readily conduct electricity, or readily

permit electric equilibrium to be established in it; or, in other words,

that it is a good insulator. This property permits the existence in it

simultaneously of materials having opposite electric charges, or the

so-called ionization phenomena; hence, water is the best-known ionizing

medium, and ionization favors chemical reactivity.

Again, water has a very high specific heat, a fact which is of the utmost

biological importance. It takes more heat to raise the temperature of one

gram of water through one degree than is required to produce the same

result in any other known substance; or, stated the other way around, a

given amount of heat will cause less change in temperature of water than of

any other known substance. Further, the latent heat of liquefaction and of

vaporization (i.e., the amount of heat required to change the substance

from solid to liquid and from liquid to gaseous state, respectively) is

greater for water than for any other common substance. These facts are of

very great importance in cell-protoplasm. The high specific heat of water

provides that the heat liberated by the chemical reactions which take place

in the protoplasm can be absorbed by the water of the cell contents, and

given off again to other reactions, with very slight effect upon the

temperature of the protoplasm itself. Hence, violent changes in

temperature, which might be disastrous to the life of the cell, are

prevented by the high specific heat of the water which it contains.

Similarly, the high latent heat of liquefaction of water, resulting in the

giving up of large quantities of heat before it can become solid, or

"freeze," tends to prevent freezing and thawing of the cell contents with

sudden changes of external temperatures at or near the freezing temperature

of water.

As a result of its physical properties, as just briefly described, water

accelerates all kinds of chemical reactions in protoplasm, both by solution

and by ionization of such substances as undergo electric dissociation; and

serves to regulate the temperature of the protoplasmic mass. Furthermore,

in organic tissues, most of the important chemical reactions of the

protoplasm are reversible hydrolyses; i.e., water actually enters into the

reaction or is liberated by it, and the equilibrium point of the reaction

is changed by the proportions of water which are present in the reacting

mass. Hence, the presence of large proportions of water in the colloidal

complex known as protoplasm has a very important influence upon its

possibilities of biological reactions.

SALTS

Active protoplasm contains mineral salts in solution. These are of the same

general nature as those found in sea-water, which is the original habitat

of the earlier evolutionary forms of living matter. Or, it might be said

that both plants and sea-water derive their mineral salts from the same

source, namely the soluble salts of the soil. Recent investigations have

shown that the proportions of sodium ions to calcium ions in sea-water are

precisely those which maintain fats, proteins, etc., in a true colloidal

emulsion; and that comparatively small variations in the ratio of these two

cations produce very marked effects upon the colloidal conditions of these

substances in an artificial colloidal preparation, which resemble very

closely the changes which apparently take place in cell protoplasm under

the influence of narcotics, or nerve stimulants, in blood-coagulation, in

the parthogenetic development of germ cells, in cancerous growth of

tissues, etc. In other words, in so far as it has been studied in this

respect, cell plasma exhibits exactly the same responses to variations in

the proportions of salts (electrolytes) in solution, that artificial

emulsions of oils (fats) in water do; and the normal, or critical,

equilibrium proportion of these electrolytes for all colloidal complexes is

that in which they occur in sea-water. It must be admitted that there is as

yet no definite evidence that the observations which have been made upon

the protoplasm of animal tissues will apply equally well to plant cell

protoplasm. But many of the phenomena which have been studied in animal

tissues have what are apparently similar, if not identical, effects in

plant tissues, and it seems reasonable to suppose that these conclusions

apply generally to protoplasm of either animal or plant origin.

The effects which salts produce in protoplasm are undoubtedly due to the

fact that, when in solution, they readily ionize and conduct the electric

current. A discussion of the nature and importance of the theory of

dissociation of electrolytes in solution, or the so-called "ionization

theory," which has done so much to clear up otherwise unexplainable

properties of solutions, would be out of place here. But it may be noted

that the ionized condition of salts in solution accounts for the avidity,

or "strength," of acids and bases; for the increased osmotic pressure of

such solutions; for the conduction of the electric current through

solutions; and for the effects of these dissolved electrolytes upon the

colloidal condition of many substances, since this is due to the electric

charge on the dispersed particles.

Hence, the presence of salts in solution in the water of the protoplasm has

a tremendous influence upon the osmotic pressure (which governs the

movement of dissolved materials into and out of the cell protoplasm); upon

the colloidal condition of the cell contents (which controls all the

effects due to the surface boundary phenomena which are discussed below and

which are responsible for a large part of the remarkable chemical activity

of the protoplasm); upon the electrical phenomena (which constitute many of

the stimulations which the protoplasm receives); and upon the acidity or

alkalinity of the cell contents (which determine the nature of the

respiratory, or oxidation, reactions of the protoplasm and, indirectly, its

life or death).

The general nature of these physical-chemical properties of the protoplasm

and of the relation of electrolytes in solution to them may now be

considered in some detail.

OSMOTIC PRESSURE

Osmotic pressure is one of the chief factors in controlling the amount of

water in the protoplasm. As is well known, the phenomenon known as

"osmosis" is the passage of solvents, or of dissolved substances, into or

out of any tissue, or substance, through the membrane which surrounds it.

In the case of a cell, the membrane in question may be either the cell-wall

or the internal colloidal films which are distributed throughout the entire

mass of the cell contents.

From the standpoint of their relation to osmosis, membranes may be either

_impermeable_, in which case neither solvent nor dissolved materials can

pass through them; _semi-permeable_, which permit the passage of the

solvent, but not that of dissolved crystalloidal substances; or

_permeable_, which permit the free passage through them of both solvents

and solutes. The first and last of these types of membranes have no effect

upon osmotic pressure; but osmotic pressure is at once set up whenever a

semi-permeable membrane is interposed between solutions of different

concentrations. It is due to the molecular motion of both the liquid and

the dissolved solids, as a result of which a greater number of molecules

are "bombarding," or pressing upon the membrane from the side of the more

concentrated solution. This sets up an unequal pressure upon the two sides

of the membrane, and if the latter be semi-permeable there will result a

passage of the liquid through the membrane toward the denser solution so as

to equalize the pressure. The resultant tendency is for the solutions on

the two sides of the membranes to become equal in concentration by movement

of the liquid from the less dense to the more dense portion, instead of by

movement of the dissolved materials toward the less dense part of the

solution as in the case of diffusion when solutions of different

concentrations are brought in contact with no membrane to interfere with

free diffusion.

Osmotic pressure tends, therefore, to force the movement of solvents

through semi-permeable membranes from more dilute toward more concentrated

solutions. Protoplasm acts in general as an approximately semi-permeable

membrane or material. For example, if the concentration of sugar in any

given mass of protoplasm becomes greater, by reason of the photosynthetic

activity, osmotic pressure is set up and water enters the mass, thus

preventing loss of turgidity due to increased concentration. Similarly, any

other increase in concentration of synthetic products is compensated for by

entrance of water because of increased osmotic pressure, unless the

products are insoluble and, therefore, incapable of effecting the osmotic

pressure.

Hence, osmotic pressure provides for the movement of water into and out of

protoplasm and so tends to keep the proportion of water uniform throughout

the entire tissue. It will at once occur to the reader, however, that if

the statements in the preceding paragraph were unqualifiedly true, and if

the protoplasmic mass were absolutely semi-permeable in character, there

would be no possibility of the passage of dissolved solids into or out of

the cell; i.e., if the protoplasm acted as an ideally semi-permeable

membrane, only water could pass into or out of it. But we know that mineral

salts from the soil must pass into any cell before the synthesis of

proteins, etc., can proceed, and that the fats, carbohydrates, proteins,

etc., which are synthetized in vegetative cells pass from these to other

organs of the plant for use or storage. The obvious explanation for this

condition of things in the plant is that protoplasm (and, indeed, this is

equally true for practically all known membranes) is not absolutely

impermeable to dissolved crystalloids; or, in other words,

semi-permeability generally means only that the solvent passes through the

membrane more readily and more rapidly than do the dissolved materials in

it. Even colloidal materials will diffuse through most common membranes,

although at so slow a rate that the process is scarcely observable by

ordinary methods of study. Hence, the actual permeability of the protoplasm

permits the movement of both water and dissolved solids from one part of

the organism to another; but its approximation of semi-permeability

produces osmotic pressure and induces freer movement of water than of

dissolved substances, and so provides for turgidity of the cells and for

equalization of the water content of different portions of the protoplasmic

mass.

It is clear, therefore, that osmotic pressure plays an important part in

the physical mechanism of cell activities and in the regulation of the

proportion of water contained in the protoplasm, with its consequent

effects upon the chemical reactions which may go on in the cell.

Actual measurements of the osmotic pressure of plant cell have been made.

The results are more or less uncertain, because, as has been pointed out, a

plant cell is not a definite quantity of uniform protoplasm surrounded by

an ideal semi-permeable membrane, but is instead a mass of living matter

which is approximately semi-permeable throughout its entire volume and is

in a constantly changing condition because of the anabolic and catabolic

activities which are going on in it; but values have been obtained which

show a normal osmotic pressure as high as fourteen atmospheres in the cells

of very turgid plants, such as those of some of the green algæ. Animal

cells probably have an osmotic pressure similar to that of the blood which

circulates around them, which is approximate that of seven atmospheres.

SURFACE BOUNDARY PHENOMENA

In the preceding chapter, a brief consideration of the phenomena arising at

surface boundaries was presented. It was pointed out that when any

substance exists in the colloidal, or dispersed, condition, it has

relatively enormous surface area and that, consequently, enormous surface

boundaries between the dispersed phase and the dispersion medium exist in

all colloidal mixtures. Since protoplasm is conceived to exist in the form

of a colloidal gel, having a foamlike structure, it is apparent that it

has these enormous surface boundaries between the different phases of the

system, and that the phenomena arising from this condition are of great

importance in its biological activities. The following necessarily brief

discussion will serve to give some indication of the physiological

importance of the surface boundaries in such a system.

It is easy to see that the molecules which are in the surface layers at the

interface, where two phases of a colloidal system are in contact, are under

the influence of forces quite different from those which are acting upon

the molecules in the interior of either phase. It is apparent that the

molecules in the surface layer are exposed on the inner side to the

attraction and influence of similar molecules, while on the opposite, or

outer, side they are exposed to the influence of molecules of an entirely

different kind. This results in a state of tension, known as "surface

tension," with the development of resultant forces and energy which

profoundly affect the chemical reactivity of the molecules which are

present in this surface layer. The so-called "surface energy," which

results from this surface tension, produces marked increases in the

possibility of chemical reaction between the materials which are present at

the surface boundaries. In colloidal gels, this effect is so pronounced, in

many cases, as to completely overshadow other types of influences upon

reaction velocities. Also, the surface layer of a liquid is compressed by

its surface tension, to such an extent that the solubility of substances in

this surface layer is greatly increased over that of the same substances in

the interior of the liquid, which results in greatly increased

concentration of dissolved substances in the surface layer, and so

increases the rate of chemical changes which take place there, as

contrasted with the rate of the same reactions going on in the interior of

the solution. This latter consideration seems to be the factor of largest

influence in colloidal catalysis.

But in addition to the increased rate of reaction in the surface layer due

to the increased energy available there and to the increased concentration

of dissolved substances, there is the possibility that the act of

concentration itself bring into play molecular forces which give rise to a

resultant increase in chemical potential, or chemical affinity, of the

reacting materials, such as has been observed to result in other

concentrated solutions. A discussion of the theoretical and mathematical

considerations upon which this conception is based would be out of place

here, but there is ample experimental evidence to indicate its soundness.

Further, as has been pointed out, colloidal phenomena are essentially due,

in large part at least, to the electric charges on the dispersed particles.

Electric charges accumulate at the surface of any charged body. Hence, the

surface layers in any colloidal system carry its electric charges in

highest concentration, and all of the chemical changes which are stimulated

by electrical phenomena are most strongly influenced at the surface

boundaries between the different phases of the system. This latter

consideration affords a satisfactory explanation of the well-known

depressing, or stimulating, action of electrolytes, especially acids and

bases, upon the enzymic catalysis of protoplasmic reactions.

These few, brief statements are sufficient to indicate how extensively the

chemical activities of colloidal protoplasm are influenced by the phenomena

arising from the surface boundaries between different materials, which are

present in such enormous extent in a colloidal gel. Surface boundary

phenomena in a heterogeneous system, such as we have seen protoplasm to be,

provide the possibilities for many reactions which would otherwise take

place very slowly, if at all. Mere subdivision of the protoplasmic

materials into the film, or foam, structure brings into play energies which

may predominate over all other types of energy in the system. Here, too,

effects may be extraordinarily modified by slight changes in environment,

which effects could not be explained by any considerations which govern

ordinary chemical reactions. Here, we deal with adsorption and other

colloidal phenomena, rather than with ordinary stoichiometric combinations.

Indeed, it is not too much to say that the differences between the

chemical phenomena which are called "vital" and those which take place in

ordinary laboratory reactions are due to the fact that the former are

manifestations of the interchanges of energy between the different phases

of a heterogeneous colloidal system, while the latter are governed by the

laws of ordinary stoichiometric combinations.

ELECTRICAL PHENOMENA OF PROTOPLASM

The investigations of this phase of the physical chemistry of protoplasm

have dealt almost exclusively with animal tissues and reactions, and have

included the study of such phenomena as nerve impulses, muscular

contractions, heart-beats, glandular secretions, etc. Tissues which respond

to nerve, or brain, control are, of course, not found in plants. But there

is plenty of experimental evidence to show that plant protoplasm carries

electrical charges and exhibits electrical phenomena which are similar in

character to those of animal tissues. In fact, it has been shown that the

contraction of the lobes of the Venus' fly trap, when they close over an

imprisoned insect, are accompanied by electrical phenomena in the leaf

tissues which are precisely similar to those which take place in an animal

muscle when it contracts. It seems probable that many of the observations

and conclusions which have been derived from the study of the electrical

disturbances in animal tissues may later be found to have definite

applications to the vital phenomena of plant cells. Hence, it seems proper

to give some brief consideration to these matters here.

The statement has been made that "every active living cell is essentially

an electric battery," and it is believed that every activity of living

matter, such as the rhythmic contraction of the heart, the passage of a

nerve impulse, etc., is accompanied by an electric disturbance in the

protoplasm of the tissues in question. Experimental proof of this

electrical disturbance has been repeatedly obtained, by connecting a

delicate galvanometer in a circuit through the living tissue which is

undergoing different activities and obtaining widely varying readings of

the instrument as the different phenomena are in progress, or by connecting

the instrument with muscular tissue and observing its fluctuations with

either the irregular contractions of a voluntary muscle or with the

rhythmic contractions of a heart muscle.

By means of such investigations as those just mentioned, it has been found

that the part of the protoplasm which is most active is always

electro-negative to the part which is less so; that is, the electric

current flows from the more active to the less active portion of the

protoplasm.

Many different explanations of the origin of the electric current which

develops when the protoplasm is stimulated into activity have been

suggested; but none of them have, as yet, any experimental confirmation.

The most that can be said is that whenever any stimulus excites the

protoplasm into activity, there is instantly developed in it an electrical

disturbance, which continues as long as the action is in progress. Recent

investigations, which have shown that there is a direct relation between

many of the vital processes of protoplasm and the ratio of the electrolytes

which it contains, particularly the ratio of sodium and potassium to

calcium, would seem to indicate that the development of the electrical

disturbance is a direct result of variations in the proportions of the

salts of these metals, either brought about by, or themselves causing,

changes in the permeability of the protoplasm, following the stimulus which

determines the nature of the activity which it is to undergo. But there is

as yet no indication concerning the mechanism by which this stimulation,

with its resultant electrical phenomena, is transmitted to the protoplasm

and accomplishes its characteristic effects.

ACIDITY OR ALKALINITY OF PROTOPLASM

The preceding sections of this chapter have dealt almost exclusively with

the physical properties of protoplasm; including the phenomena of solution,

ionization, surface boundary effects, and electrical disturbances, and

their probable effects upon the chemical reactions which constitute its

biological activities. It is necessary now to consider another phase of the

physical chemistry of protoplasm, namely, its chemical reaction, whether

acid, alkaline, or neutral, the effects of variation of this condition upon

the activity of the protoplasm, and the mechanism by which it tends to

preserve its own proper reaction in this respect.

The earlier methods of investigation of the chemical reaction of

protoplasm were all based upon its color reactions to various staining

agents. These sometimes led to erroneous conclusions, because of the

effects of the staining agent itself upon the tissue; some stains are

poisonous and result in the death of the protoplasm, others do not easily

penetrate the semi-permeable colloidal mass, others are themselves changed

by the oxidizing or reducing action of the protoplasm, etc. Again,

colloidal adsorption effects often lead to the so-called "capillary

segregation" of added staining materials. So that this method of study must

be used with great care, or wholly erroneous conclusions will be reached,

and many of the earlier reports have subsequently been found to be

incorrect.

The recent improvements in the apparatus and methods for the determination

of hydrogen-ion concentration have afforded a much more trustworthy method

of determining the actual acidity or alkalinity of such materials than is

obtained by color reactions, and this method is now being extensively used

in the study of the reaction of active protoplasm.

It must be kept in mind that protoplasm is an heterogeneous mass and not an

homogeneous solution, so that it is not always possible to determine the

actual conditions as to neutrality of different parts of the protoplasm of

a single cell, for example. Hence, one of the best methods of determining

the reaction which is favorable to the life and activity of any given type

of protoplasm is to investigate the reaction of a liquid medium in which

the cells live and grow; this plan being based upon the assumption that a

cell is not likely to have a reaction different from that of the medium

which is favorable to its growth.

The results of all of the many investigations which have dealt with this

problem point to the conclusion that the normal reaction for living

protoplasm is either neutral or very faintly alkaline; but that it becomes

acid when the cell is working in the absence of sufficient oxygen, and

after the death of the cell.

The first effect of a change in the reaction toward acidity of the

protoplasm is a decrease in the rate of respiration of the tissue, while

increased alkalinity stimulates respiratory activity. Whet carried to the

point of actual acidity, the respiratory coefficient becomes negative, and

the cell actually gives off carbon dioxide because of the stoppage of the

synthetic processes.

A second effect of change in reaction of protoplasm is to alter the enzymic

activity of the cell. As has been pointed out, enzymes are extraordinarily

sensitive to minute changes in the reaction of the medium in which they are

working. A change toward acidity in protoplasm immediately results in the

stimulating of carbohydrate-splitting enzymes, which increases the supply

of easily oxidizable simple carbohydrates, thereby tending to compensate

for the decrease in respiratory activity. Further, increase in acidity

increases proteolysis, thereby liberating alkaline ammonia-derivatives

which tend to neutralize the rising acidity and so to restore normal

neutrality or alkalinity. Thus it will be seen that in the very great

sensitivity of its enzyme catalysts to slight changes in the reaction of

the medium, the protoplasm possesses a very efficient mechanism for

regulating changes and restoring equilibrium, if the latter be disturbed by

any abnormal conditions. It should also be noted, at this point, that the

almost universal presence in protoplasm of salts of carbonic and phosphoric

acids acts as an additional "buffer" against pronounced changes in reaction

of the material; the bicarbonates acting by means of their ready release or

absorption of carbon dioxide, and the phosphates by their easy change from

mono-sodium phosphate to di-sodium phosphate, and _vice versa_, the former

being slightly acid and the latter slightly alkaline in reaction.

A third effect of increasing acidity is that it induces increased

imbibition of water by the colloidal gel and causes swelling of the tissue.

After death, when the reaction of the protoplasm becomes pronouncedly acid,

this swelling often proceeds to the point of rupturing of the cell-wall, or

internal membranes of the protoplasm, thus permitting the entrance of the

putrefactive bacteria and hastening the decay of the tissue.

Finally, comparatively slight variations in the reaction of the protoplasm

produce enormous changes in its colloidal condition, affecting in a very

marked degree its permeability, its power of adsorption, etc.

It is clear, therefore, that variations in the chemical reaction of

protoplasm profoundly affect its colloidal condition, its enzymic activity,

and its respiratory processes. This necessarily brief survey is sufficient

to indicate how important to the activity of the protoplasm is the chemical

reaction of the material, and the mechanism with which it is provided for

maintaining the favorable condition of neutrality or slight alkalinity.

SUMMARY

It is evident that, within the limits of a single chapter, it has been

possible to give only a very brief and incomplete discussion of some of the

most important applications of the principles of physical chemistry to the

properties and activities of protoplasm. Therefore, it may be profitable to

summarize briefly these into a series of definite statements which may

serve as a review of the principles which have been discussed in the

preceding chapters, as applied to the activities of protoplasm.

Protoplasm is a complex hydrogel, composed of an heterogeneous mixture of

proteins, fats, and carbohydrates, arranged in a foamlike structure, the

compartments of the gel being filled with an aqueous solution of the

soluble organic products of synthesis and of varying proportions of mineral

salts which are of the same general nature as those of sea-water.

The gel is not uniform throughout the volume of any given cell, but is

differentiated in different parts into what are known as the nucleus, the

chloroplasts, the plasma of the cell, etc.

The vital activities of the cell consist in chemical reactions which are

controlled by comparatively slight changes in the electrolyte distribution,

or other environmental changes which affect the colloidal condition of the

mass and, generally speaking, result in changes of the water content of the

plasma, most such chemical changes being essentially reversible hydrolytic

reactions.

The components of active protoplasm are in a condition most favorable to

chemical reactions by reason of the enormous surface area of the colloidal

material, resulting in abundance of available energy, intimate contact of

the reacting materials, and the nearest possible approach to the condition

of true solution which can be obtained without the loss of stable form and

structure.

The reactions which take place in cell protoplasm, as a result of the

action of either physical or chemical stimuli, are accompanied by

electrical disturbances, which may be either caused by, or the result of,

changes in the electrical charges of the mineral salts which are present in

the gel. Such changes, like the chemical reactions which they accompany,

may be regarded as reversible and mutually self-regulatory; so that the

protoplasm has not only the possibilities of enormous chemical reactivity,

but also the mechanism for self-regulation of its actions, the products or

results from any given series of changes generally tending to reverse the

process by which they are proceeding and so to restore the condition of

normal equilibrium.

Finally, the most characteristic difference between the reactions which go

to make up the vital activities of a living cell and those of the same

chemical substances when in inanimate form in the laboratory lies in the

presence in the colloidal mass of the accelerating catalysts known as

enzymes, which are produced by the protoplasm itself in some way which is

as yet wholly unknown; and which not only add to the possibilities of rapid

chemical change which are afforded by the colloidal nature of the material,

but also, because of their extreme sensitiveness to minute changes in

environmental conditions, serve to govern both the rate and the direction

of the individual chemical reactions which constitute the vital activities

of the protoplasmic mass. These enzymes are not distributed uniformly

through any given cell, or organism, but are localized in different parts

of the cell or tissue and so give to its different parts the ability to

perform their various different functions.

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28 figs., London, 1916.

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1912.

HÖBER, M. R.--"Physikalische Chemie der Zelle und der Gewebe," 671 pages,

55 figs., Leipzig, 1911.

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149 pages, Chicago, 1903.

MCCLENDON, J. F.--"Physical Chemistry of Vital Phenomena," 248 pages,

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1917.

WILLOWS, R. S. and HATSCHEK, E.--"Surface Tension and Surface Energy and

their Influence on Chemical Phenomena," 116 pages, 21 figs., New York,

1919, (2d ed.).

CHAPTER XVII

HORMONES, AUXIMONES, VITAMINES, AND TOXINS

Reference has frequently been made, in preceding chapters, to the effect of

various stimulating or inhibiting agencies upon the physiological

activities of plant protoplasm. In the main, these agencies are _external_

to the plant and are either physical, such as changes of temperature,

amount of light received, etc.; or chemical, such as variations in the

salts received from the soil, or common anæsthetics applied to the plants

by man. A plant grows normally under certain conditions to which it has

become adjusted by hereditary acquirements. When these conditions are

altered, the effect upon the functioning of the plant protoplasm may be

either stimulating or depressing. Extreme changes in environmental

conditions generally result in the death of the plant; but changes which do

not result in the lethal condition affect the plant by either stimulating

it to more rapid physiological activity or by depressing its normal growth

or functions. As has been pointed out, the same external influence, either

chemical or physical, which acts as a stimulant if it differs only slightly

from normal conditions, may become depressing, or positively toxic, if

present to a larger extent.

There is also the possibility of the elaboration by the plant itself of

_internal_ agents, or substances, which may have a definite stimulating or

inhibitory effect upon its metabolism and growth. The study which has been

given to these matters has practically all been carried on within very

recent years and is still in progress. Most of it is still in the

experimental stage, in which no definite conclusions are as yet possible.

Hence, the most that can be done at present is to give a brief review of

the suggestions which have been made thus far, as indicative of the

uncertainty of our present knowledge of these matters and of the general

trend of the investigations which are now in progress.

Substances which are elaborated by plants and which are supposed to have a

definite stimulating or beneficial effect upon the activities of the plant

which produces them, or to influence the physiological activities of other

plants with which these substances come in contact through either the

parasitic or the symbiotic relation, have been variously discussed under

the names "hormones," "auximones," and "vitamines"; while injurious

substances are generally known as "toxins." Whether these different terms

actually represent different definite types of substances, or whether there

are actually different groups of stimulating or inhibitory agents produced

in plants, is uncertain; but the following brief statements will serve to

indicate the general nature of the suggestions which have been put forward

and of the experimental work which is now in progress.

HORMONES

The term "hormone" was first used to designate certain stimulating

substances which are supposed to exist in the intestinal tracts of animals

and to cause the glands to elaborate and secrete their characteristic

enzymes. The supposed "hormones" are not themselves active in performing

the digestive functions of the glandular secretions, but are the exciting,

or stimulating, agents which cause the glands to secrete their active

enzymes.

The same term has been used, by certain plant physiologists, to designate

any agency, either external or internal, which stimulates plant protoplasm

to abnormal activity. It has been pointed out that there are a variety of

substances, which are themselves chemically neutral, that are powerful

stimulants of vital activity if used in only minute proportions, but are

powerful poisons if present in larger amounts. Many of the alkaloids act in

this way upon the animal organism; while chloroform, toluene, and even some

of the more complex hydrocarbons, act similarly upon the tissues of plants,

and ether vapor is known to be a powerful stimulant in accelerating the

flowering of plants and the ripening of fruits. It has been shown that the

vapors of all such substances readily penetrate the protoplasm of leaves,

seeds, etc., even when the same parts are impermeable to most mineral

salts, sugars, etc.; and that upon entrance to the protoplasm of a leaf, or

a seed, they tremendously stimulate its metabolic activity. These

hormones, as a class, are chemical substances which have very little

attraction for, or power of combination with water; and it has been

suggested that the ease with which they penetrate the protoplasm is due to

the fact that they are not held at the surface by combination with the

active water molecules which are present in the surface layer.

The principal effect which is supposed to be produced by these "hormones"

is the stimulation of the enzymic activity, particularly that of the

degenerative processes which take place late in the plant's life, at the

flowering or ripening periods. Many of the changes which take place

normally at ripening time, such as the change in color from green to yellow

or red and finally to brown or black, when the fruit or vegetable is fully

ripe, can be greatly accelerated by treatment with these substances.

Hormones are similar in type to the ethereal salts, or esters, which

constitute the natural essential oils that develop in many plants at this

stage of their growth. Hence, it seems probable that these changes in

plants which are maturing naturally may be hastened by the hormone action

of the esters and similar bodies which are developed in largest quantities

at that stage. It has been pointed out that the characteristic group which

is present in many natural glucosides is of the same general type as the

"hormone" substances which are used in the artificial stimulation of the

flowering or ripening changes. This fact, together with the possibility of

the liberation of greater percentages of these aromatic compounds from

their glucoside combinations at the later periods of plant growth, is

assumed, by some plant physiologists, to account for the change from

synthetic to degenerative processes at this stage of the plant's

development.

Further, it has been suggested that the autumnal coloration of leaves, and

their dropping from the stems of the plant, as well as the ripening of

seeds, is probably determined by the liberation in the plant, at that stage

of its growth, or as a result of changed climatic conditions at that

particular season of the year, of the hormones which either initiate or

hasten the special enzymic changes which distinguish the degenerative from

the synthetic processes of the plant.

Similarly, it has been suggested that parasitic fungi are able to penetrate

the host plant by first excreting "hormones" which bring about degenerative

changes in the tissues of the host plant and so make it more easily

penetrable by the hyphae of the parasite.

It will be seen that, in general, "hormones" are a type of substances

(possibly often present in plants in the form of glucosides) which are

supposed to stimulate the degenerative (or katabolic) vital processes in

contrast to the synthetic (or anabolic) changes. It has been suggested that

they do this in either one of two ways; namely, by favoring the

introduction of water into the protoplasm and so diluting the cell

contents, changing the osmotic pressure, etc.; or by bringing about a

separation of the colloidal layers, or films, of the protoplasmic complex,

producing a result similar to that produced by freezing the tissues. These

ideas have been suggested by studies of the changes in the equilibrium of

protoplasm when foreign substances are introduced into it. These studies

have not as yet been brought to the stage of final conclusions, and the

ideas presented must be considered as suggestive rather than as conclusive.

VITAMINES

"Vitamines," as contrasted with "hormones," are supposed stimulants of

synthetic metabolic processes, or accelerators of growth, rather than of

degenerative processes.

The term "vitamine" was first used to designate the substance, or

substances, which must be present in the diet of animals in order that the

animal organism may grow. Absence of these substances from the food of the

animal results in the stoppage of growth of young animals and in various

so-called "deficiency diseases" (such as beri-beri, scurvy, polyneuritis,

etc.) of adults. This means that the animal organism is altogether unable

to elaborate its own vitamines, and extended investigations have indicated

that the vitamines necessary for animal uses are wholly of plant origin.

The name "vitamine" was first used because it was supposed that these

substances are chemical compounds of the amine type and, since they are

necessary to normal life processes of animals, the name "vitamine" seemed

to represent both their chemical character and their functions. Later

investigations have caused doubt as to the accuracy of the first belief as

to their chemical nature, and various other names have been suggested for

the general group of substances which have the observed beneficial

effects; while such specific names as "fat-soluble A," "water-soluble B,"

etc., have been used to designate individual types of these accessory food

substances. However, the term _vitamine_ is such a convenient one and is so

generally recognized and accepted that it will probably continue to be

used, at least until some more definite knowledge of the nature and

composition of these growth-promoting, disease-preventing, and

reproduction-stimulating food constituents is obtained.

The following definition of the term "vitamines" gives a satisfactory

conception of the nature and functions of these substances, so far as they

are yet known. "Vitamines; constitute a class of substances the individuals

of which are necessary to the normal metabolism of certain living

organisms, but which do not contribute to the mineral, nitrogen, or energy

factors of the nutrition of those organisms." As sub-groups of the

vitamines, there have already been recognized the growth-promoting,

fat-soluble A; the antineuritic B, and the antiscorbutic C.

Until very recently, the investigations of vitamines have dealt exclusively

with their relation to human nutrition; although it has been generally

believed that the vitamines themselves are elaborated only by plants. It

was generally recognized, however, that those plants, or parts of plants,

which are capable of very rapid growth or metabolic changes, such as germs,

spores, leaves, etc., are generally the richest source for vitamines for

animal needs. Hence, there seemed to be considerable basis for the

assumption that the elaboration of these substances by plants is definitely

connected with their own metabolic needs. Recently, investigations of the

functions of vitamines in the growth of plants have been begun. These are

still in progress, but the following conclusions seem to be justified at

the present time: (_a_) Potato tubers appear to contain growth-promoting

substances which are essential to the proper growth of the sprouts. Whether

these are the same substances which are efficient in the prevention of

scurvy in men has not yet been investigated. (_b_) Baker's yeast is

probably dependent upon a supply of vitamines in the medium in which it is

to grow. Yeast itself, after having grown in barley wort, is one of the

most important sources of vitamines for animal uses or for purposes of

investigations of vitamine activity. But it has been reported that a yeast

cell will not grow in an artificial medium which contains all the essential

nutrients for yeast but has no vitamines of other plant origin in it. The

addition of barley wort, containing the vitamines from barley germs, or any

other similar supply of vitamines, induces rapid growth and the storage of

vitamines in the growing yeast masses. (_c_) The growth of many bacteria is

either wholly dependent upon or greatly stimulated by the presence of

vitamine-like substances in the medium upon which the microorganisms grow.

(_d_) _Sclerotinia cinerea_, the brown rot fungus of peaches and plums,

will grow only in a medium which contains, in addition to the essential

sugar, salts, and nitrogenous material, vitamines derived from either the

natural host plant tissues or other plant sources. These may be of two

types (namely, a vegetative factor and a reproductive factor) or two

different manifestations of activity of the same vitamine substance. But

both of these factors must be provided before the fungus can make its

characteristic growth.

There is, as yet, no conclusive evidence on many of the matters concerning

the relation of vitamines to plant growth. But it seems that these

substances are of almost universal occurrence in the organic world; that

they are not of the same general type as other substances which are

essential to the nutrition of plants or animals, but have specific

stimulating or regulating effects upon the physiological activities of the

organism; that the vitamines which are essential to animal life are

elaborated by plant tissues, but that in the case of the bacilli of certain

human diseases there seems to be some indication that the affected tissues

of the animal host produce vitamines which are essential, or favorable, to

the growth of the parasitic organism. There seems, therefore, to be

evidence of a mutual relation between plants and animals with respect to

their nutritional needs for the so-called "vitamines." But the evidence

concerning the function of these substances in the tissues of the organism

which elaborates them is, as yet, inadequate to provide any clear

conception of the reason for their development or of the mechanism by which

they are elaborated. Neither is there, as yet, any conclusive evidence

concerning the chemical nature of the substances themselves.

AUXIMONES

Certain investigations have indicated that bacteria, at least, develop

exogenous vitamines which are beneficial to the growth of other plants.

These are the so-called "auximones." For example, bacterized peat seems to

contain auximones which may be isolated from the peat and exert a

beneficial effect upon the growth of various seed-plants, including common

farm crops. Neither the original experimental data, nor the theories which

have been advanced to account for the observed beneficial effects of the

supposed "auximones" have, as yet, sufficient confirmatory evidence

definitely to establish their soundness. But it seems that there is a

probability that some plants, at least, do elaborate vitamines, or

auximones, which are useful to other plants.

TOXINS

Toxins are substances which affect injuriously the normal activities of the

organism. As has been pointed out, they may be the same substances which,

in lesser concentrations, exert a stimulating effect upon the same

organism. Hence, it is probably inaccurate to discuss the toxins as a

distinct group of substances.

There are, however, a large number of water-soluble chemical substances

which are injurious to all living protoplasm, even at concentrations

considerably less than the point of osmotic equilibrium in the juices of

the protoplasm. These substances may act either directly or indirectly upon

the protoplasm, but at certain concentrations they always affect it

injuriously. In the main, these toxins are _external_ agents of other than

plant origin; although chemical substances developed by one plant may be

toxic to other plants, or even to other organs of the same plant than those

in which they are elaborated.

Toxins may be either _general_ (i.e., injurious to all types of plants), or

_specific_ (i.e., injurious to only certain species) in their action.

Examples of specific toxicity are of only minor importance in plant

studies. They seem to be generally explainable on the basis of some unusual

lack of resistance or failure of the susceptible plants to be able to

exclude the entrance of these injurious substances into the protoplasm by

"selective adsorption," or to convert the injurious substances into

insoluble and non-injurious forms, as is done by other plants which are not

susceptible to injury by these "specific" poisons. Hence, particular

attention need not be given to this type of toxins.

Toxic substances may act injuriously upon plant tissues in a variety of

ways. Many electrolytes, especially the salts of the heavy metals of high

valency, coagulate protein material and the entrance of such substances

into the protoplasm causes disturbances in the colloidal condition which

cannot be otherwise than injurious to its normal activities. Similarly,

formaldehyde and many other organic compounds may affect the colloidal

properties of the protoplasmic gel in such a way as to injure the plant

tissues.

The same substance is sometimes much more injurious to the tissues of one

part of a plant than it is to those of another part of the same plant.

Thus, the rootlets of a young growing plant are much more susceptible to

injury by many mineral salts than are the vegetative parts of the same

plants; while anæsthetics of various kinds generally exhibit their greatest

injurious effects upon the leaves, or synthetizing cells. Again, the

mycelia of fungi are much more easily killed by toxic agents used as

fungicides than are the spores of the same fungi. Some of these observed

differences in toxicity may be due to differences in the physiological

effect of the substance upon the protoplasm of the tissues which it enters,

and others may be due to differences in the resistance of the protoplasm,

or of its protective coverings, to penetration by the toxic material.

Indeed, the possibilities of different types of toxic action, and of

resistance to it by individual plants and species, are so varied that it is

not possible to divide toxic agents into specific groups according to the

nature of their injurious action upon the plant cell. They are, therefore,

more commonly grouped into classes according to their chemical nature and

economic significance as fungicides, as follows: inorganic and organic

acids; caustic alkalies; salts of the heavy metals; hydrocarbon gases;

formaldehyde; alcohols and anæsthetics; nitrogenous organic compounds; and

miscellaneous decomposition productions of organic origin. The following

brief review of some of the results of the experimental studies of the

toxicity of different compounds belonging to these several groups will

serve to indicate the general trend of the investigations of these matters

which have thus far been made.

=Acids.=--The common inorganic acids (hydrochloric, nitric, and sulfuric)

kill the rootlets of common farm crops when the latter are immersed for

twenty to twenty-four hours in solutions of these acids containing from

three to five parts per million of free acid. Acetic acid must be about

five times as concentrated as this, and other organic acids may be much

more concentrated still before they produce the same injurious effects. The

toxic effect of all these acids is greatly reduced in soil cultures, or if

particles of sand, graphite, clay, filter paper, etc., are suspended in the

solutions containing the acids, the reduction in toxic effect being

probably due to the adsorption of the acids upon the solid particles.

Hence, the concentrations which limit the toxic effects of these acids in

water solutions cannot be taken as representing the condition with which

the same plant will have to contend when growing under normal cultural

conditions.

=Alkalies.=--The caustic alkalies must usually be present in from five to

ten times as great concentrations as those of the mineral acids, in order

to produce the same injurious effects upon the rootlets of common plants.

The so-called "alkali" of soils is not alkali at all, but is neutral

soluble salts present in sufficient concentration to exert a toxic effect.

=Salts of the heavy metals= are especially toxic to rootlets of plants.

Salts of copper, mercury, and silver, have been found to kill the roots of

seedlings immersed in them for twenty-four hours when present in

proportions of less than three parts per ten million, while salts of many

other heavy metals are toxic when present in concentrations of less than

one part per million. The salts of the alkali metals are considerable less

injurious than are those of the heavy metals, but even these exert their

familiar injurious effect if present in concentrations which, measured by

the ordinary standards, would still be regarded as very dilute solutions.

=Illuminating gas=, and similar hydrocarbon gases, kill plants when present

in the atmosphere in as little as one part per million. Leaves, buds, and

roots are all alike sensitive to this toxic effect, the nature of which is

not yet understood.

=Formalin=, or formaldehyde, is a penetrating toxic agent for nearly all

plant cells, and is commonly used as a fungicide for the destruction of

parasitic fungi. It probably affects the colloidal condition in some way

similar to its hardening effect upon gelatin, etc.

The toxic effect of many different =organic compounds= is so varied in its

nature and extent that it is impossible to give any satisfactory brief

review of its manifestations. Recent investigations appear to indicate that

organic products of decomposition of plant residues in the soil may exert

powerfully toxic effects upon succeeding generations of the same, or of

different, plants growing on the land. But the experimental data and

conclusions concerning these matters are not yet accepted without question

by all students of plant science or of the problems of the productivity of

the soil. In fact, it is yet an open question whether toxic soil

constituents are really an important factor in the so-called

"unproductivity" of certain soils.

Alkaloids, and even the amino-acids which are produced in the tissues of

some species of plants, while not toxic to the plants or organs which

elaborate them, sometimes exhibit strikingly toxic action upon other plant

organs with which they are brought into contact. There is, as yet, no

satisfactory explanation of this difference in behavior between plant

tissues toward various organic toxic substances.

In fact, the whole subject of the toxic action of various substances upon

plants needs much more study before it is brought to the point where it

will afford definite knowledge of either the physiological problems

involved or of their practical applications in questions of soil

productivity, etc.

CHAPTER XVIII

ADAPTATIONS

Most of the discussions which have been presented in the preceding chapters

have dealt with the types of compounds, the kinds of reactions, and the

mechanism for the control of these, which are exhibited by plants under

their normal conditions for development. The results of the evolutionary

process have produced in the different species of plants certain fixed

habits of growth and metabolism. So definitely fixed are these that in each

particular species of plants each individual differs from other

individuals, which are of the same age and have had the same nutritional

advantages and environmental opportunities for growth, by scarcely

perceptible variations, if at all. Indeed, this fixed habit of development

makes possible the classification of plants into genera, species, etc.

While _different species_ of plants, given the same conditions of nutrition

and environment, produce organs of the widest conceivable variety in form,

color, and function; within the _same species_, the form and size of

leaves, the position and branching of the stem, the color, size, and shape

of the flower, the coloration and markings of the fruit, etc., are

relatively constant and subject to only very slight modifications.

It is unnecessary to say that the mechanism, or the impulses, which govern

the morphological characters of the tissues which any given species of

plants will elaborate out of the crude food material which it receives from

the soil and atmosphere, are wholly unknown to science. It is the commonly

accepted assumption that the fixed habit of growth of the species is

transmitted from generation to generation through the chromosomes of the

germ cells. But the nature of the elements, or substances, which may be

present in the chromosomes, which influence the character of the organs

which will develop months later, after the plant which grows from the germ

cell has gone through its various stages of vegetative growth, is still

altogether unknown. There can be no question, however, that some influence

produces a fixity of habit of growth and development which is almost

inevitable in its operation.

But while this unvarying habit of growth is one of the fixed laws of plant

life, there are occasional deviations from it. A plant which, under normal

conditions of growth, develops in a certain fixed way, when exposed to

unusual environmental conditions, may, and often does, alter its habit of

growth in what may metaphorically be said to be an attempt to adjust itself

to the new conditions. Numerous examples of this phenomenon might be cited.

Certain algæ, which grow normally in water at a temperature of 20° to 30°

and which are killed if the temperature rises above 45°, have been grown

for successive generations in water the temperature of which has been

gradually raised, until they produce apparently normal growth in water the

temperature of which is as high as 78°; also, certain types of algæ

normally grow in the water of hot springs at temperatures of 85° to 90°,

and others in arctic sea-water the temperature of which sometimes falls to

-1.8° and never rises above 0° C. This phenomenon of the adjustment of a

species of plants to new conditions, which in the case of farm crops is

sometimes called "acclimatization," is of common occurrence and is often

utilized to economic advantage in the introduction of new strains of crops

into new agricultural districts. Again, the normal development of plants

may be altered as the result of injury or mutilation. Thus, if the ear is

removed from the stalk of Indian corn, at any time after flowering, there

always results an abnormal storage of sucrose in the stalk, instead of the

normal storage of starch in the kernels. Similarly, midsummer pruning of

fruit trees generally results in the production of abnormally large number

of fruit buds on the remaining limbs. Many other familiar examples of

alteration of normal development in response to, or as the result of,

abnormal conditions of growth might be cited.

TYPES OF ADAPTATIONS

To designate these different alterations of normal growth, several

different terms have been used. Among these, "adaptation," "accommodation,"

and "adjustment" have been commonly used by different biologists. Sometimes

these are used interchangeably, and sometimes different terms are used to

designate different types of response to altered conditions of growth.

Inasmuch as there seems to be no generally accepted usage of these

different terms, only one of them, namely, the word "adaptation" will be

used here; and different manifestations of this phenomenon will be

distinguished by using appropriate adjectives, as "physiological

adaptations," "chromatic adaptations," "morphological adaptations," etc.

Two markedly different types of responses to altered conditions, or of

adjustment to environment, may be recognized. In the first of these, for

which we will use the term "physiological adaptation," the species of plant

simply acquires the ability to exist and grow normally under conditions

which formerly inhibited its growth. Thus, we may speak of the phenomena

mentioned above as "acclimatization" as the _physiological adaptation_ of

the crop to the new conditions of growth. In general, physiological

adaptations include such variations in the characters or habits of growth

of plants as results in differences in resistance to heat or to cold,

relations to water, aggressiveness in competition with other plants, etc.

In such cases, no modification of the morphological characters of the plant

can be observed, the changes which take place in the structure of the plant

(if, indeed, there be any such changes) must be only minor adjustments of

the protoplasm to meet the new environmental needs.

In the second type of adaptations, for which we will use the term

"morphological adaptations," the structure, or color, or some other

morphological character of the plant is actually changed in some easily

recognizable way, in order that the plant may be better adjusted to its

environment. As examples of _morphological adaptations_, there may be cited

the change in color of sea-weeds with increasing depth in the sea, and

other examples of chromatic adaptation which are discussed below; the

development of fewer, or a larger number, of buds on the above-ground stems

of plants, in response to decreases, or increases, in the available supply

of food; the alteration in the size and shape of the leaves of many plants

when they are grown in shade; the dwarfing of plants at high altitudes, or

under conditions of severe drought; the development of underground storage

organs for certain species of shrubs and trees which grow in regions that

are subject to periodical burning-over, in such a way as to destroy the

above-ground storage stems, etc.

Hence, the two terms, as we will use them here, may be defined as follows:

_morphological adaptation_ is a change in the structural character of the

species in order that it may be better fitted to meet the needs of the new

conditions of growth; while _physiological adaptation_ is an acquired power

to survive and develop under abnormal conditions, which is not accompanied

by any visible change in the characteristic structure of the species.

Both of these types of adjustment may be either hereditary (or

evolutionary), or spontaneous in their origin and development. Changes

which are evolutionary are fixed by heredity and become definite habits of

growth in the species. Their origin may be explained in either one of two

ways; namely, the so-called "increase by use," and "the survival of the

fittest." The hypothesis of "increase by use," as an explanation of

adaptations, is based upon the well-known observation that, in animals,

muscles and other organs increase in volume as they are extensively used;

and the assumption of the application of this principle to the phenomenon

of adaptation supposes that the modification of any given structure or

composition is the result of the hereditary accumulations of increased size

resulting from use, or of atrophy from disuse. The "survival of the

fittest" theory supposes that individuals of a species differ from each

other by spontaneous variations, and that in the competitive struggle for

existence those forms which are best adapted to the environmental

conditions survive while the others perish. The contrast between these two

views is that the first holds that adaptation proceeds by development, and

the second that it proceeds by variation and elimination; the first

presupposes the existence in the organism of a mechanism for response to

changing conditions, and the second assumes that there are chance

variations followed by the death through competition of the forms which are

not able to meet the needs of the environment.

Confusion arises whenever an attempt is made to apply either of these

theories to all kinds of adaptations. The idea of increase by use can be

applied with some satisfaction to certain morphological adaptations in

animal structure; and to such phenomena as the increase in strength of the

branches of fruit trees, either with or without corresponding increase in

size, as the load of fruit increases. But it certainly cannot apply to

color change in surface pigmentation of either animals or plants, which is

one of the most common forms of adaptation. Furthermore, it is difficult

to conceive the general application of this idea to alterations of habits

of growth of plants, since a plant cannot have any such thing as a

voluntary control over the amount of "use" which it makes of its different

organs in response to changes of environment. The common form of statement

that a plant develops an organ, or a process to meet a certain need, or

modifies its habits of growth to meet a change of environment are, of

course, purely metaphorical, and can only be taken to mean that such

processes are mechanical responses to changes in external conditions.

The nature of the mechanism by which these responses are accomplished is,

as yet, wholly unknown. There is accumulating a large mass of experimental

evidence which goes to show that, while both temperature and light are very

important factors in determining the type of changes which will take place

in a living organism, the so-called "photochemical action of light" is by

far the most potent of all the climatic factors which influence the course

of development of a plant. But we have, as yet, no inkling of how the

protoplasm of the plant adjusts or controls its responses to variations in

any of these external factors.

With these general considerations in mind, we may now proceed to the

consideration of certain particular types of adaptations.

CHROMATIC ADAPTATIONS

Adaptations have been observed in both the energy-absorbing pigments of the

general tissues and in the ornamental epidermis pigments of plants. The

former are by far the most important from the physiological point of view;

while the latter may have interesting biological significance.

Under nearly all conditions of growth of land plants, the supply of the

chlorophylls and their associated pigments provides for the absorption of

solar energy far in excess of the amount necessary for the photosynthetic

assimilation of all the carbon dioxide which is available to the plant. It

has been shown that an active green leaf, on an August day, can absorb

eight times as much radiant energy as would be required to assimilate all

the carbon dioxide present in the air over its surface. No land plant,

under normal conditions, develops supplementary pigments in order to

utilize other than the parts of the spectrum which are absorbed by

chlorophyll and its associated pigments.

But deep-sea plants show quite a different phenomenon of pigment

development. Water is a blue liquid. At depths of 40 feet or more, the

light which penetrates is devoid of red rays, feeble in yellow, and is

characteristically green or blue in color. Now, the red rays of the

spectrum are the ones which are most efficient for photosynthesis. Sea

weeds which grow at these depths are brilliantly red in color, at

intermediate depths they are brown, and at the surface they are green, in

the same latitudes. While it is possible that the temperature of the water

at these different depths may have something to do with the chemical

synthesis of the pigments, it appears plain that this color change at

increasing depths is a definite adaptation to provide for the absorption of

the solar energy which is available at these depths. It has been shown that

these pigments of deep-sea plants are additional to, and not substitutes

for, the chlorophylls, etc. The latter pigments are present in normal

amounts, but are supplemented by those which absorb the green and blue

portion of the spectrum. Hence, this type of adaptation might be conceived

to be a "survival of the fittest," resulting in the "natural selection" of

individuals of the highest total pigmentation. But, on the other hand,

there is experimental evidence to show that plants possess some means of

varying their pigmentation in response to the character of the light which

comes to them. For, it has been found that a complete change in color of

certain highly colored plants can be produced in a single generation, by

growing the plants in boxes or chambers whose walls are composed entirely

of differently colored glass, so that the plants within receive light of

only a particular part of the spectrum. In such cases, the plant, starting

with an initial "natural" color, changes through a succession of colors

until it finally reaches equilibrium at one which provides for the proper

absorption of the right kind of light from the new supply which is

available to it. Hence, it seems proper to conclude that chromatic

adaptation is not a process of "natural selection," but a definite result

of an actual mechanism for adaptation to changed environmental conditions

of supply of radiant energy.

STRUCTURAL ADAPTATIONS

Changes in structure to meet special conditions of growth may be of several

different types.

One of these, which is often cited as an example of adaptation (in this

case, the term is used with a significance quite different than that in

which it is being used here) is that of the development of unusual and

often fantastic shapes of flowers, which are so related to the anatomy of

certain species of insects that visit these flowers in search of nectar,

that provision for the cross-fertilization of the plants is insured, in

that the pollen from the anthers of one flower becomes lodged on the body

of the insect as it is withdrawing from the flower in such a way that it

comes in contact with the pistil of a second flower as the insect enters

it. Such flowers often have such peculiar shapes and lengths of nectar

tubes, etc., that only a single species of insect, whose anatomical shape

is "adapted" to that particular blossom shape can enter the flower in its

search for nectar. It is clear that this form of "morphological adaptation"

is a highly specialized one, which can only be the result of a long process

of evolutionary development. It is obvious that the plant cannot possibly

possess a mechanism, or ability, to alter its flower form in order to make

it conform to the shape and length of the proboscis, or other body parts,

of a particular species of insect. Either the insect or the plant, or both,

must go through a process of evolutionary development in order to arrive at

this form of mutual "adaptation."

A form of true morphological adaptation (in the sense in which we have been

using the term) is exhibited by many species of plants, which are provided

with many more buds, or growing points, than ever actually begin to grow.

For example, the single plumule which develops from a germinating wheat

embryo has at its upper end a hundred or more tiny growing points. At the

proper stage of its growth, several of these tiny buds begin to grow into

individual separate stems, and the new wheat plant thus produces several

stems from one seed and root system, a process known as the "stooling." The

number of stems in a single "stool" depends upon the number of the

potential growing points which are stimulated into growth. It varies from

only two or three up to as many as thirty or forty, and is apparently

controlled by the favorable or unfavorable conditions of climate or

nutrition at the time when the "stooling" takes place. The plant is thus

provided with a mechanism for adapting its possibilities of growth to the

supply of growth-promoting material which is available to it.

Many other plants produce far more buds than ever develop into growing

tissues, and buds which, under normal conditions, remain dormant, under

altered conditions start into growth and so provide for an "adaptation" of

the total mass of the growing plant to correspond with the altered

conditions of growth. The actual means by which certain buds are stimulated

into growth while others remain dormant, or are inhibited from growing, are

as yet unknown. Two theories have been advanced. One is that the growing

buds absorb all available nutrition and the others remain dormant by reason

of lack of growth-promoting material. The other is that the vegetating

(growing) tissue elaborates and sends to other parts of the organism one or

more substances, which actually inhibit growth of the other parts, as

dormant buds, etc. The experimental evidence which has been presented thus

far is inconclusive, but seems to favor the distribution of nutritional

material as the governing factor, although there is some evidence which

seems to indicate that a supposed growth-inhibiting substance is actually

translocated from rapidly-vegetating tissues to other parts of the plant.

There is, however, no explanation of how the buds, or other tissues, which

do grow get their initial stimulus, while the dormant buds do not. After

growth has once started, the changes in osmotic pressure due to the

accumulation and translocation of synthetized materials can account for the

movement of new nutritional material for the synthetic processes into the

growing organ; but this would not account for the selective stimulation of

only a part of the buds, or possible growing points, of a plant, or for an

adaptational development of others under altered conditions of growth.

The form of morphological adaptation which has been discovered in the

course of the study of the native vegetation of the campos of Brazil (which

have a very dry season and have been regularly burned over by the natives

for many generations) in which the papilionaceous shrubs have developed

underground trunks, or stems, and seem actually to profit in luxuriance of

growth when the rainy season comes on by reason of this morphological

adaptation to the unusual environmental conditions, is wholly inexplicable

by any present knowledge of the science of plant growth.

PHYSIOLOGICAL ADAPTATIONS

The type of adjustment to environmental conditions which does not result in

any recognizable alteration in the structure of the plant, but simply

permits it to grow under new conditions, manifests itself in many ways.

These adjustments are usually associated with differences in temperature

during the growing season, and for this reason, most such examples of

adaptation have been studied in connection with possible temperature

reactions upon the growing organism.

However, recent investigations seem to point strongly to the conclusion

that the amount of _light_ rather than the _temperature_ of the new

surroundings is the most important influence in determining the

physiological processes known as the "acclimatization" of plants. For

example, a very elaborate series of investigations has shown that the

flowering stage in the development of plants is determined by the length of

the daylight period per day, irrespective of the actual amount of

vegetative growth which the plant has made. Thus, tobacco plants, which

during a period of long days grow to the height of 8 or 10 feet before

blossoming, if grown at the same temperature in periods of short days (or

if kept in the dark during a portion of the longer days) will blossom when

less than 3 feet in height and when the total mass of vegetative material

which has been produced is less than one-third of that of the "gigantic"

plants of the same variety grown with longer periods of illumination per

day. This same principle has been found to hold good for many widely

different types of plants. In some species, however, flowering is favored

by long days, and vegetative growth by short daylight illumination. But in

all species which have been studied, there seems to be a direct relation

between the length of day, or the total illumination per day, and the

normal or abnormal functioning of the plant. It is apparent that at least

the physiological function of sexual reproduction (flowering and

seed-production) is determined by the length of daylight illumination. The

duration of daylight per day which is necessary to induce the blossoming of

the plants varies for different species, but it is constant for individuals

of the same species. This adaptation of stage of growth to duration of

daily illumination must, therefore, be an evolutionary character of the

species.

Hence, it appears that in many cases physiological adaptation may be a

direct response of the life-processes of the plant to the daily length of

photochemical stimulation which it receives from solar light. But there is,

as yet, no explanation of how this (or any other) influence actually

changes the vital processes of the plant protoplasm so as to bring about

either a morphological adaptation of structure or a physiological

adaptation of functions to altered conditions of growth.

CONCLUDING STATEMENTS

Enough has been said to show how very inconclusive and unsatisfactory is

our knowledge of the phenomena known as "adaptation." Even the nomenclature

used by different scientists to describe its various manifestations is

confused and misleading. For example, certain crops are said to be

"adapted" (i.e., suited) to certain types of soils, and _vice versa_; crops

are said to be "adapted" to given agricultural districts, etc.

In this chapter, an attempt has been made to arrange in some semblance of

order some of the known manifestations of alteration of fixed habits of

growth of plants in response to changes of environment, and to point out

some of the suggestions of possible explanations of these phenomena which

have been presented by different investigators.

This presentation cannot be considered as anything other than an

introduction to a field of study which is as yet almost entirely

unexplored, and, like all other unexplored territory, is full of mysteries.

If the study of this chapter serves to stimulate interest in these

mysteries and wonders of plant life, its purpose will have been

accomplished.

INDEX

Bold-face figures indicate main references

Accelerators, 196.

Accessory substances, 19.

Achroo-dextrin, 61.

Acid, acetic, 125, 126, =128=, 132, 133, 166.

arabic, 68.

arachidic, 133.

aspartic, 168, 177.

brassic, 133.

butyric, 126, 133.

capric, 133.

caprylic, 133.

carnaubic, 140.

cerotic, 133, 140.

citric, 125, 127.

convolvulinic, 81.

crotonic, 133.

diamino-oxysebacic, 169.

diamino-trioxydodecanic, 169.

digallic, 96.

ellagic, =96=.

euxanthic, 84.

formic, 25, =126=, 128, 132.

galactonic, 42.

gallic, =96=.

geddic, 69.

gluconic, 42.

glucuronic, 42, 43.

glutamic, 168, =177=.

glycero-phosphoric, 142.

hydrocyanic, 77.

jalapinic, 81.

lauric, 133.

lignoceric, 133.

linoleic, 133.

linolenic, 133.

malic, 124, =127=.

malonic, 124.

mannonic, 42.

melissic, 133.

meta-pectic, 68, =70=.

mucic, 68.

myristic, 133.

nitric, 125.

nucleic, =162=.

oleic, 133.

oxalic, 68, 124, 125, =126=, 128.

palmitic, 133, 140.

parapectic, 70.

pectic, =31=, 70.

phosphoric, 141, 142, =162=.

propionic, 126, 166.

pyrocatechuic, 96.

quercitannic, =98=.

racemic, 54.

ricinoleic, 133.

ruberythric, =83=.

saccharic, 42, 68.

salicylic, 81.

sarco-lactic, =128=.

stearic, 131, =133=.

succinic, =127=, 128.

sulfuric, 125.

sylvinic, 149.

talonic, 42.

tannic, 97, =127=.

tartaric, =127=.

uric, =160=.

xanthoproteic, 173.

Acid amides, 151.

Acidity of protoplasm, =234=.

Acid glucosides, 81.

Acid potassium oxalate, 125.

Acid potassium sulfate, 88.

Acid salts, =124=.

Acids as toxins, =246=.

Acid sodium sulfate, 125.

Acrolein, 135.

Acrose, 28.

Activators, 196.

Adamkiewicz's reaction, 173.

Adaptations, =249=.

Adenase, 190.

Adenine, =160=, 162.

Adipo-celluloses, =74=.

Adsorption, =214=.

Æsculetin, 81, 82.

Æsculin, =81=, 82.

Ætiophyllin, 106, 107, 109.

Ætioporphyrin, 108, 109, 110.

Alanine, 168, 177.

Albumins, 175, 176.

Albuminoids, 175, 176.

Alcogel, 205.

Alcohol, ethyl, 40, 125.

benzyl, 80.

carnaubyl, 135.

ceryl, 135, 140.

cetyl, 129, 135.

coniferyl, 80.

melissyl, 135.

myricyl, 129, 140.

phytyl, 104, =105=.

polyhydric, 31.

Alcohol glucosides, 80.

Alcosol, 205.

Aldehyde, benzoic, 148.

cinnamic, 148.

formic (_see_ formaldehyde).

glyceric, 35.

Aldehyde glucosides, 80.

Aldehydrol, 46.

Aldonic acids, 42, 44.

Aldose, 32.

Alizarin glucosides, 78.

Alkalinity of protoplasm, 234.

Alkalies as toxins, =247=.

"Alkali salts," 10, =247=.

"Alkali soils," 10, =14=.

Alkaloidal reagents, 154, 172.

Alkaloids, 18, 20, 151, =153=, 248.

Allose, 36, 37.

Allyl isosulfocyanide, 88, 89, 148.

Allyl sulfide, 148.

[alpha]-glucose, 46.

[alpha]-glucosides, 55.

[alpha]-methyl glucoside, =47=.

Altrose, 36, 37.

Aluminium, =4=.

Amandin, 170, 176.

Amines, =151=.

Amino-acids, 6, 151, =166=, 179, 248.

Ammonia, 152.

Ammonium hydroxide, 142, 152.

Ammonium salts, 6.

Amorphous chlorophyll, 104, 105

Amphoteric electrolytes, 172.

Amygdalase, 87.

Amygdalin, 81, =86=.

Amyl acetate, 148.

Amylase, 186, 189, =191=.

Amylo-cellulose, 60.

Amylo-dextrin, 61.

Amylo-pectin, 60.

Amylose, 60.

Anergic food, =2=, 17.

Animal nucleic acids, =162=.

Antagonism, 14.

Anthocyans, 83, 102, =115=, 121.

Anthocyanidins, 116.

Anthocyanin, 102.

Anthoxanthins, =117=.

Anthraquinone, 83.

Antienzymes, 120, =197=, 198.

Antioxidase, 120.

Antiscorbutic C, 243.

Apigenin, 84, 118.

Apiin, =84=.

Apiose, 84.

Araban, =69=.

Arabinose, 35, 44, 68, 69, 88.

Arabinosides, 56.

Arbutin, 77, =79=.

Arginine, 169, 171, 177.

Arsenic, 13.

Asymmetric carbon atom, 33.

Atropine, 155, =156=.

Autotrophic plants, 16, 18.

Auximones, 239, 240, =244=.

Available plant food, =4=.

Avenalin, 176.

Baptigenin, 79.

Baptisin, =79=.

Beeswax, 133.

Beet sugar (_see_ sucrose).

Berberine, 155.

Betaine, =152=.

[beta]-glucase, 55.

[beta]-glucose, 46.

[beta]-glucosides, 55.

[beta]-methyl glucoside, 47.

Biogens, 223.

Biological significance, =19=.

Biuret reaction, 173.

Borneol, 148.

Boron, 13.

Bromelin, 189.

Brucine, 155, =157=.

Buffers, 236.

Butter fat, 133.

Butyric acid ferment, 190.

Cadaverine, 152.

Caffeine, =160=.

Calcifuges, 9.

Calciphiles, 9.

Calcium, 3, 5, =9=, 10, 14, 68.

Calcium oxalate, 126.

Campferitrin, 118.

Campferol, 118.

Camphene, 147.

Camphor, 148.

Cane sugar (_see_ sucrose).

Caoutchouc, =147=.

Capillary segregation, 235.

Carbohydrases, 189.

Carbohydrates, 18, 20, =21=, =30=, 163, 234.

Carbon dioxide, 2, 3, 18, =21=, 22, 23, 24, 40, 222.

Carbonic acid, 227.

Carbon monoxide, 24.

Carboxyl, 124.

Carboxylases, 186, 190.

Carnauba wax, 133, 140.

Carotin, =112=, 113, 121.

Carotinoids, 102, =111=.

Carvacrol, =148=.

Casein, 165.

Castanin, 176.

Castor oil, 130.

Catalases, 190, 193.

Catalysis, 182.

Catalysts, 17, 25, 183.

Catechol tannins, 97.

Catechin, =97=.

Catechu tannins, =97=.

Cellobiose, 52.

Cell structure, 221.

Cellulase, =71=, 186, 189.

Celluloid, 73.

Cellulose, 20, 45, 63, 67, =72=.

Cell-wall, 9, 12, 222.

Cerebrosides, 141, =144=.

Chemical resistance, 216.

Cherry gum, 68.

Chinovose, 35.

Chlorine, =12=.

Chlorophyll, 10, 11, 21, 27, =102=, 105, 110, 111, 113, 122, 254.

Chlorophyll _a_, 103, 106, 107, =111=.

Chlorophyll _b_, 103, 106, 108, =111=.

Chlorophyllase, 104.

Chlorophyllin _a_, 106, 107.

Chlorophyllin _b_, 106, 107.

Cholesterol, 129, =136=.

Choline, 89, 103, 141, 142, =152=.

Chromatic adaptations, 251, =253=.

Chromogens, 92, 119.

Chromo-proteins, 175.

Chrysin, 117.

Cinchonine, 155, =157=.

Coagulated proteins, 175.

Coagulation enzymes, 190.

Cocaine, 155, =157=.

Cocoanut oil, 133.

Codeine, 155, =158=.

Coenzymes, =197=.

"Cold-drawn oils," 137.

Collodion, 73.

Colloidal phenomena, 17, =202=.

Colloidal solutions, 204.

Colloids, 202.

Colophene, 147.

Colophony, 149.

Compound celluloses, 71, =73=.

Conglutin, 176.

Coniferin, =80=.

Coniine, 155, =156=.

Conjugated proteins, 165, 174, =175=.

Continuous phase, 203.

Convolvulin, =81=.

Copper, 13, 247.

Cork tissue, 99, 101.

Corn oil, 130.

Corylin, 176.

Cottonseed oil, 130.

Critical elements, 4.

"Crude fat," 141.

Crystalline chlorophyll, 104, 105.

Crystalloids, 202.

Cumarin, 81, 148.

Curarine, 157.

Cuto-celluloses, =74=.

Cyanidin, 85, 116.

Cyanin, =85=.

Cyanophore glucosides, 86.

Cyanophyllin, 107, 108.

Cyanoporphyrin, 108.

Cymarigenin, 90.

Cymarin, =90=.

Cymarose, 90.

Cystine, 168, 171.

Cytase, 72, 189.

Cytosine, 161, 162.

Daphnetin, 81, 82.

Daphnin, 81.

Deaminases, 186, 190.

Delphinidin, 85, 116.

Delphinin, =85=.

Derived proteins, 173, =175=, 177.

Dextrin, 59, =61=.

Dextrinase, 189.

_d_-galactose, 33.

_d_-glucose, 33.

Dextrosans, 59.

Dextrose (_see_ glucose).

Dhurrin, =87=.

Diastase (_see_ amylase).

Diastase of secretion, =191=.

Digitaligenin, 89.

Digitalin, =89=.

Digitogenin, 89.

Digitonin, =89=, 90.

Digito-saponin, 90.

Digitoxigenin, 89.

Digitoxin, =89=.

Digitoxose, 89.

Diglycerides, 131.

Diose, 30.

Dioxyacetone, 35.

Dipeptides, 167.

Disaccharides, 31, =48=.

Dispersed phase, 203.

Dispersion medium, 203.

Dispersion phenomena, 203.

Drying oils, 132.

Dulcitol series, 36.

Edestin, 170, 176.

Egg-albumin, 165.

Electrical phenomena of protoplasm, =233=.

Electrolytes, 213, 227.

Emulsoids, 206, 214.

Emulsions, 206.

Emulsin, 55, 77, 87, 184, 189.

Enol, =44=, 56.

Enzymes, 17, 18, 19, 20, 23, 26, 120, 121, =181=, 183, 194, 199, 224.

Erepsin, 189.

Erythro-dextrin, 61.

Erythrophyllin, 107.

Erythrose, 35.

Essential elements, 4.

Essential oils, 18, 146, =147=, 224.

Esterases, 186, 189.

Esters, 124, 125, 129.

"Ether extract," 141.

Etherial salts (_see_ esters).

Ethersol, 205.

Ethyl acetate, 125.

Ethyl nitrate, 125.

Excelsin, 176.

Extracellular enzymes, 184.

Fats, 18, 20, =129=, 224, 227.

Fat-soluble A, =243=.

Fatty acids, 132, 142.

Fehling's solution, 39, =47=.

Fermentability, =40=.

Ferments (_see_ enzymes).

Ferric salts, 11.

Ferrous salts, 11.

Fisetin, 118.

Flavone, 82, 83, 102.

Flavonol, 84.

Food, =1=.

Formaldehyde, =22=, 23, 25, 26, 27, 247.

Frame-work material, 20, 67.

Fraxetin, 82.

Fraxin, =82=.

Fructose, 23, 28, 32, 36, 38, 41, 44, 45, =47=, 57, 162.

Fructosides, 41, 42.

Fruit sugar (_see_ fructose).

Fucose, 35.

Fucoxanthin, 102, 112, 114.

Galactans, 47, 59, =63=, 72.

Galactoheptose, 36.

Galactooctose, 36.

Galactose, 32, 36, 38, 45, =47=, 57, 72, 77.

Galactosides, 41, 42.

Gaultherin, 81.

Gel, 172, 205, 208.

Gelation, 210.

Gel-formation, =208=, 211.

Gentianose, 52, =53=.

Gentiobiose, 49, =52=, 53.

Gentisin, 119.

Gitaligenin, 89.

Gitalin, =89=.

Gitogenin, 89.

Gitonin, =89=.

Glaucophyllin, 107.

Gliadin, 165, 170, 176.

Globulins, 170, 175, 176.

Glucase, 186.

Glucodecose, 44.

Glucoheptose, 36, 44.

Glucononose, 36.

Glucooctose, 36.

Glucoproteins, 175.

Glucose, 23, 28, 32, 36, =37=, 40, 41, 42, 43, 44, 45, 46, 57, 77.

Glucosidases, 189.

Glucosides, 18, 20, 41, 48, 55, =76=, 91, 93.

Glue, 210.

Glutelins, 175, 176.

Glutenin, 176.

Glycerine (_see_ glycerol).

Glycerol, 129, 131, =134=, 142.

Glycine, 166, 168, 177.

Glycinin, 176.

Glycogen, 59, =61=.

Glycyphyllin, =79=.

Graminin, 59, =62=.

Granulose, 60.

Grape sugar (_see_ glucose).

Guanase, 190.

Guanine, =160=, 162.

Gulose, 36, 37.

Gum arabic, =68=.

Gums, 62, 67, =68=.

Gum tragacanth, =69=.

Gun-cotton, 73.

Hæmatin, 110.

Hæmatinic acid imide, 109.

Hæmatoporphyrin, 110.

Hæmoglobin, 110.

Hæmopyrrole, 109.

Helicin, 81.

Hemi-celluloses, 63, =71=.

Hemi-terpenes, 147.

Heptoses, 30.

Hesperidin, =79=.

Hesperitin, 79, 80.

Heterotrophic plants, 16.

Hexosans, 59, 67.

Hexoses, 22, 28, 30.

Histidine, 169, =177=.

Histones, 175, 176.

Honey sugar (_see_ fructose).

Hordein, 153, 170, 176.

Hormones, 92, 239, =240=.

"Hot-drawn oils," 137.

Humins, 67.

Hydrastine, 155.

Hydrazones, 40, 49.

Hydrocellulose, 73.

Hydrogen peroxide, 26, 27, 190.

Hydrogel, 205.

Hydrolases, 186, 189.

Hydroquinone, 77, 79.

Hydrosol, 205.

Hydroxy-phenyl ethyl amine, 153.

Hygrine, 155, 156.

Hyoscine, 155.

Hyoscyamine, =156=.

Hypoxanthine, =160=.

Idain, =85=.

Idose, 36, 37.

Illuminating gas as a toxin, 247.

Imbibition, 209.

Impermeable membranes, 228.

Indian yellow, =84=.

Indican, 78, =85=.

Indigo, 78, 84.

Indigotin, 85.

Indole, 158.

Indoxyl, 85.

Inhibitors, 196.

Intracellular enzymes, 184.

Inulin, 59.

Inulinase, 62, 189.

Invertase, 50, 189, =191=.

Invert sugar, 47, 50.

Iodine number, 138.

Ionization phenomena, 226.

Iridin, =79=.

Irigenin, 79, 80.

Iron, 3, 5, 11, 110.

Isochlorophyllin _a_, 106, 107, 108.

Isochlorophyllin _b_, 106, 107, 108.

Isohæmopyrrole, 109.

Isoleucine, 168.

Isomaltose, 51.

Isomerism, 32.

Isoprene, 147.

Isoquercitrin, 84.

Isoquinoline, 155.

Jalapin, =81=.

Japan wax, 129.

Juglansin, 176.

Ketose, 32.

Lactam, 104.

Lactase, =56=.

Lactic acid ferment, 190.

Lactone, 104.

Lactose, 45, 49, 52.

Laudanosine, 158.

Laudanum, 158.

Lecithin, 7, =141=, 142, 143.

Lecithoproteins, 175.

Legumelin, 176.

Legumin, 170, 176.

Leucine, 115, 168, =177=.

Leucomaines, 152.

Leucosin, 176.

_l_-galactose, 33.

_l_-glucose, 33.

Levulosans, 59, =62=.

Levulose (_see_ fructose).

Lichenin, =62=.

Light, 21, 253, 257.

Lignocelluloses, =74=.

Lignose, 31.

Limettin, =82=.

Limonene, 147.

Linalyl acetate, 148.

Linseed oil, 133.

Lipases, 186, 189.

Lipins (_see_ lipoids).

Lipoids, 129, =140=.

Lipoproteins, 175.

Lupinine, 155.

Lycopersicin, 102, 122, =114=.

Lysine, 169, 171, 177.

Lyxose, 35.

Magnesium, 3, 5, 9, =10=, 11, 13, 14, 68.

Maltase, 55, 184, 189.

Maltose, 45, 49, =51=, 52.

Malvidin, 85.

Malvin, =85=.

Mandelo-nitrile, 78, 88.

Mandelo-nitrile glucoside, 77, 87.

Manganese, =4=, 13.

"Manna," 47.

Mannans, 59, 62, =63=, 72.

Mannite, 47.

Mannitol, 47.

Mannitol series, 36.

Mannoheptose, 36, 44.

Mannononose, 36.

Mannooctose, 36.

Mannosans (_see_ mannans).

Mannose, 32, 36, 37, 41, 44, 45, =47=, 57, 72.

Mannosides, 42.

Maple sugar (_see_ sucrose).

Maysin, 176.

Melibiose, 49, =52=.

Melizitose, =52=.

Menthol, 148.

"Mercerizing" cotton, =73=.

Mercury, 247.

Merosinigrin, 88.

Metallic salts, 13, 224, 227, 237, 247.

"Metal proteids," 14.

Meta-pectin, 70.

Metaproteins, 175.

Methylethylmalein imide, 108.

Methyl glucosides, 42.

Methyl pentoses, 35.

Methyl salicylate, 81.

Middle lamella, 67, 70.

Millon's reaction, 173.

Molisch's reaction, 174.

Monoglycerides, 131.

Monohydric alcohols, 135.

Monosaccharides, 31, =35=, 45.

Morin, 119.

Morphine, 155, =158=.

Morphological adaptations, 251, 252, =255=.

Mucilages, 67, =70=.

Muco-celluloses, 74.

Muscarine, =152=.

Mustard oils, 88, 148.

Mustard oil glucosides, 88.

Mutarotation, 46, 49.

Myrosin, 77, 88, 149, 189.

Myrtillidin, 85.

Myrtillin, =85=.

Narceine, 158.

Narcotine, 158.

"Natural selection," 254.

Neurine, 152.

Nicotine, 155, =156=.

Nitrates, 6.

Nitrile reaction, =43=.

Nitriles, 43, 44.

Nitrogen, 3, 5, 6, 151, =164=.

Non-drying oils, 132.

Non-essential elements, 4.

Non-reducing sugars, 39, 49.

Nonoses, 31.

Normal celluloses, =72=.

Nuclease, 189.

Nucleoproteins, 162, 175.

Nutrients, 1.

Octoses, 31.

[OE]nidin, 85, 116.

[OE]nin, =85=.

Oils, =129=.

Oil of bergamot, 148.

Oil of bitter almonds, 86, 148.

Oil of cassia, 148.

Oil of cinnamon, 148.

Oil of garlic, 148.

Oil of lavender, 148.

Oil of mustard, 148.

Olive oil, 130.

Opium, 158.

Organic acids, 18, =124=, 248.

Organized ferments, 183.

Ornamental pigments, =102=, 123.

Ornithine, 169.

Oryzenin, 176.

Osazones, 40, 41, 49.

Osmotic pressure, 213, 228.

Osones, 41.

Oxidases, 186, 190, 193.

Oxime, 44.

Oxycellulose, 73.

Oxycumarin glucosides, 81.

Oxygenated oils, =147=.

Oxyhydroquinone, 95.

Oxyproline, 169.

Pæonidin, 85.

Pæonin, =85=.

Palm oil, 133.

Papain, 189.

Papaverine, 155, =158=.

Para-dextran, 62.

Para-isodextran, 62.

Paralyzers, 196.

Para-pectin, =70=.

Parasites, 16.

Peanut oil, =133=.

Pectase, 71.

Pectinase, 189.

Pectins, 20, 31, 67, =70=.

Pecto-celluloses, =74=.

Pectose, 31, 70.

Pelargonidin, 85, =116=.

Pelargonin, =85=.

Pentosans, 31, 67, 68, 72.

Pentoses, 30, 162.

Pepsin, 167.

Peptids, =166=, 167, 176.

Peptones, 176.

Permeable membranes, 228.

Peroxidases, 190.

Persimmons, 100.

Persuelose, 36.

Phæophytin, 107, 108.

Phaselin, 176.

Phaseolin, 176.

Phenol, 95.

Phenol glucosides, =79=.

Phenyl alanine, 168, =177=.

Phenyl hydrazine, 40.

Phlein, =62=.

Phloretin, 79.

Phloridzin, =79=.

Phloroglucinol, 95.

Phosphates, 7.

Phosphatides, 141, =143=.

Phosphoproteins, 175.

Phosphorus, 3, 5, =7=.

Photo-chemical action of light, 253, 257.

Photolysis, 26.

Photosynthesis, 7, 8, 18, 21, 22, =24=, 254.

Phycoerythrin, 102, =115=.

Phycophæin, 102, =115=.

Phyllins, 106, 107.

Phyllophyllin, 107.

Phyllopyrrole, 109.

Physiological adaptations, 252, =257=.

Physiological use, =19=.

Phytase, 189.

Phytochlorin, 108.

Phytorhodin, 108.

Pigment glucosides, =82=.

Pigments, 18, =102=, 224, 254.

Pinene, 147.

Piperidine, 154.

Piperine, =155=.

Plant amines, =151=, 152, 163.

Plant food, =1=.

Plant nucleic acids, =162=.

Polybasic acids, 124.

Polyhydric alcohols, 31.

Polypeptides, 167.

Polysaccharides, =59=.

Polyterpenes, 147.

Poppy wax, 140.

Populin, =80=.

Porphyrins, 108.

Potassium, 3, 5, 8, 10, 13, 14.

Primary amines, 152.

Proenzymes, 198.

Proinulase, 199.

Proinvertase, 199.

Prolamins, 175, 176.

Proline, 169, 177.

Prolipase, 199.

Prooxidase, 199.

Protamines, 175, 176.

Proteans, 175.

Proteases, 186, 189, =192=.

Protective colloids, 209.

Proteins, 7, 18, 20, 151, 162, 163, =164=, 224.

Proteoses, 175.

Protoplasm, 17, 26, 221.

Prulaurasin, 87.

Prunase, 87.

Prunasin, 87.

Ptomaines, 152.

Purine, =159=.

Purine bases, 151, =159=, 162.

Purpurin, 83.

Putrescine, 152.

Pyrimidine, 161.

Pyrimidine bases, =161=, 162.

Pyrocatechol, 95.

Pyrogallol, 95.

Pyrogallol tannins, =97=.

Pyroxylin, 73.

Pyrrophyllin, 107.

Pyrridine, 154.

Pyrrolidine, 154.

Quaternary amines, =152=.

Quercetin, 84, 118.

Quercitrin, =84=.

Quinine, 155, =157=.

Quinoline, 155, 158.

Radiant energy, 19.

Raffinose, 45, 52, =53=.

Rape-seed oil, 130.

Reducing sugars, 39, 49.

Reductases, 186, 190.

Reserve food, 21.

Resenes, 149.

Resins, 18, 146, =149=.

Resorcinol, 95.

Respiration, 18, 121, 235, 236.

Rhamnase, =77=, 189.

Rhamnetin, 84.

Rhamnose, 35, 52, 77, 79.

Rhodeose, 35, 81.

Rhodophyllin, 107.

Ribose, 35.

Ricin, 176.

Rubiadin, 83.

Rubiphyllin, 107.

Saccharide, =31=.

Salicin, =80=.

Saligenin, 80.

Salinigrin, =81=.

Salts, 224, =227=, 237.

Sambunigrin, 87.

Sapogenins, 90.

Saponification, 134.

Saponification value, 138.

Saponins, =90=.

Sapotoxins, 90.

Saprophytes, 16.

"Saturated" acids, 132.

Scopolin, =82=.

Secalin, =63=.

Secondary amines, 152.

Secretions, 20.

Sedoheptose, =36=.

Semipermeable membranes, =228=.

Sensitizers, 27.

Serine, 168.

Silicates, 12.

Silicon, 4, =12=.

Silver, 247.

Simple proteins, 165, 174, =175=.

Sinalbin, 89.

Sinalbin mustard oil, 89.

Sinapin acid sulfate, 89.

Sinigrin, =88=.

Sinistrin, =62=.

Sitosterol, 136.

Skimmetin, =81=, 82.

Skimmin, =81=.

Soaps, 134, 208.

Sodium, 4, 9, =12=, 13, 14.

Sodium stearate, 133.

Sol, 205.

"Soluble starch," 60.

Sorbitol, 48.

Sorbose, 36, 38, 45, =48=.

Specific rotatory power, =38=, 39.

, of fructose, 39, 47.

, of galactose, 49.

, of glucose, 39, 47.

, of maltose, 51.

, of raffinose, 53.

, of sucrose, 39.

Spermaceti, 129, 133.

Stachydrine, 155.

Stachyose, 54.

Starch, 8, 22, 28, 30, 31, 45, =59=, 64.

"Starch paste," 60.

Stearin, 131, 134.

Stereo-isomerism, =32=.

Stigmasterol, 136.

Structural adaptations, =255=.

Structural isomerism, =32=.

Strychnine, 155, =157=.

Substrate, 186.

Sucrase (_see_ invertase).

Sucrose, 28, =49=, 64.

Sugars, 8, 18, 22, 28, 30, 31.

Sulfur, 3, 5, =11=, 148.

Sulfuretted oils, 147, =148=.

Sulfur test, 174.

Sunflower-seed oil, 130.

Surface boundary phenomena, =231=.

Surface energy, 231.

Surface tension, 231.

"Survival of the fittest," 254.

Suspensoids, 206, 214.

Suspensions, 206.

Synergic foods, 2, 20.

Synthesis, 18.

Tagatose, 36, 38, 57.

Talose, 36, 38, 42, 57.

Tannins, 18, =94=, 97, 99, 100, 127, 208, 224.

Tannon group, 96.

Terpenes, =147=.

Tertiary amines, 152.

Tetrapeptids, 167.

Tetrasaccharides, =54=.

Tetrose, 30, 35.

Theobromine, =160=.

Theophylline, =160=.

Thioglucose, 88.

Threose, 35.

Thymine, 161, 162.

Thymol, 148.

Toxins, 13, 239, 240, =245=.

Translocation diastase, 191.

Trehalase, 51.

Trehalose, 49, =50=.

Triglycerides, 131.

Trimethyl amine, =152=.

Trimethyl glycocoll, 143.

Triose, 30, 35.

Trioxymethylene, 22, 23.

Tripeptids, 167.

Trisaccharides, 31, =52=.

Triticin, 59, =62=.

Tryptophane, 169, 171, 177.

Tuberin, 176.

Turanose, =49=, =53=.

Tyndall phenomena, 212.

Tyrosine, 115, 168, 177.

Unavailable plant food, 4.

Ultrafilter, 215.

Ultramicroscope, 203, 204, 205, =211=.

Unorganized ferments, 183.

"Unsaturated" acids, 132, 138.

Uracil, 161, 162.

Urease, 190.

Valine, 168.

Vanillin, 80, 148.

Vegetable bases, 18, =151=.

Vicianin, 88.

Vicilin, 176.

Vignin, 176.

Vitamines, 239, 240, 242.

Volatile oils, 20, 147.

Water, 3, 21, 22, 23, =224=.

Water-soluble B, 243.

Waxes, 18, 129, =140=.

Weathering, 4.

Wood gum, 68.

Wool fat, 129.

Wound gum, 68, =69=.

Xanthine, =160=.

Xanthone, 82, =83=, 102.

Xanthophyll, 112, =113=, 121.

Xanthopurpurin, 83.

Xanthorhamnin, 52, =84=.

Xylan, =69=.

Xylose, 35, 68, 69.

Xylosides, 56.

Yeast, 61.

Zein, 165, 170, 176, 177.

Zinc, 13.

Zymase, 51, 56, 190, =192=.

Zymogens, =198=.

Transcriber's Notes:

The original spelling and minor inconsistencies in the spelling and

formatting have been maintained.

The following words have been variably hyphenated in the original:

oxy(-)cumarin, tri(-)saccharides, sugar(-)like, mono(-)saccharides,

sea(-)weeds, di(-)sodium, foam(-)like, di(-)basic, aldo(-)hexoses,

chromo(-)proteins, galacto(-)octose, gluco(-)octose, keto(-)hexoses,

ligno(-)celluloses, manno(-)octose, para(-)pectic, di(-)saccharides,

poly(-)saccharides. The variable hyphenation has been retained in this

version.

Formatting:

Text in italics was marked using underscores (_text_) and bold text using

equals (=text=).

The greek characters alpha and beta were marked as [alpha] and [beta]

Triple bonds were marked as [trb] in order to keep the lt1-text. Vertical

double bonds are marked with a broken bar ¦.

On page 120 the illustration of the decomposition of chlorophyll a and

chlorophyll b could not be displayed due to its complex structure.

On page 147 the incorrect formulas of sitosterol, C_{27}H_{43}OH and

stigmasterol, C_{30}H_{49}OH were not changed due to the fact that the pure

compounds were first isolated in 1926 after this book was published.

The table below lists all corrections applied to the original text.

p 3: Abderhalden's "Biochemische Handlexicon" -> Handlexikon

p 10: with the blood pigment, haematin -> hæmatin

p 15: special type, or unusual origin. -> [period added]

p 17: that the photo-synthesis -> photosynthesis

p 20: Experiments with algae -> algæ

p 21: that when algae -> algæ

p 26: Experiments," 294 pages, 49 -> [period deleted]

p 36: acts as a powerful anaesthetic -> anæsthetic

p 40: Die Chemie der Chlorophyll -> Die Chemie des Chlorophylls

p 41: many other poly-atomic -> polyatomic

p 54: Left parenthesis at C6 of Aldopentose deleted

p 55: glucose yeilds -> yields

p 60: see pages -> see page

p 61: when heated to 82 C° -> 82° C

p 65: power of +148.° -> +148°.

p 67: attack other dissacharides -> disaccharides

p 74: Secalan -> Secalin

p 77: Erganzungsband -> Ergänzungsband

p 77: Handbuch der Kohlenhydrate," -> [closing quotes added]

p 86: Erganzungsband -> Ergänzungsband

p 88: has not yet been determined. -> [period added]

p 87: by a plane hexagon, thus [Illustration: hexagon]. -> [period added]

p 95: C_{21}C_{20}O_{12} -> C_{21}H_{20}O_{12}

p 96: blue grapes, _oenin_ -> _[oe]nin_

p 96: glucose + oenidin -> [oe]nidin

p 97: reactions of amydalin -> amygdalin

p 98: reactions of amgdalin -> amygdalin

p 107: Gallic acid, -> [period changed to comma]

p 112: Diospyrus -> Diospyros

p 114: the following formulas: -> [semicolon changed to colon]

p 121: obtained from aetioporphyrin -> ætioporphyrin

p 121: that from ætioporphryin -> ætioporphyrin

p 122: chlorophylls are fluorescent, -> [period changed to comma]

p 122: and red by reflected -> [comma deleted]

p 122: properties of these pigments, -> [period changed to comma]

p 123: roots of carrots, etc., -> [second period changed to comma]

p 123: due to these pigments. -> [period added]

p 124: OH groups an addition -> OH groups in addition

p 124: Buchner funnel -> Büchner funnel

p 126: that it contains leucin -> leucine

p 126: leucine and tyrosin -> tyrosine

p 134: Willsttäter -> Willstätter

p 135: malonic acid -> [space added]

p 137: C_{3}H_{5}·COOH -> C_{3}H_{7}·COOH

p 138: commercially as a bye-product -> by-product

p 146: of the experiment. Microörganisms -> Microorganisms

p 154: or through its basic (OH) group -> or through its basic (N) group

p 158: oxygenated and sulphuretted -> sulfuretted

p 161: Aetherische Oele, Harze, -> [comma added]

p 161: F. trans. -> [period added]

p 162: HEUSLER, F., [additional comma added]

p 164: ergot, and hordeine -> hordein

p 171: C_{5}H_{4}N_{4}O_{2}, -> [comma added]

p 171: gaunine -> guanine

p 177: CH_{3}·CHNH·COOH -> CH_{3}·CHNH _{2}COOH

p 179: monoamino-monocarboxylic acids: -> [period changed to colon]

p 181: Hystidine -> Histidine

p 181: Amadinn -> Amandin

p 184: which contains tyrosin -> tyrosine

p 184: or a tyrosin-containing -> tyrosine-containing

p 185: nitric acid on tyrosin -> tyrosine

p 186: acids, or alkalies. -> [period added]

p 187: Juglansin, -> [comma added]

p 187: of walnut and butternut. -> [period added]

p 187: barley. -> [period added]

p 192: reactions when caried -> carried

p 197: which accelerates the hydyrolysis -> hydrolysis

p 198: are further sub-divided -> subdivided

p 200: Butryic acid ferment -> Butyric acid ferment

p 202: and other microörganisms -> microorganisms

p 203: alcohol and carbon dixoide -> dioxide

p 205: especially tyrosin -> tyrosine

p 206: masses under the ultra-microscope -> ultramicroscope

p 212: J. trans -> J., trans. -> [comma added]

p 218: chemical nature and dialectric -> dielectric

p 231: Dresden and Leipsig -> Leipzig

p 231: Leisegang -> Liesegang

p 231: Beitrage -> Beiträge

p 233: observed under the ultra-microscope -> ultramicroscope

p 236: is undoubtedly tetravalent, [period changed to comma]

p 237: has a higher dialectric -> dielectric

p 239: As in well known -> As is well known

p 241: the organism to amother -> another

p 242: having a foam-like -> foamlike

p 249: Bestimmung der Oberflachenspannung -> Oberflächenspannung

p 249: The Role of Diffusion -> The Rôle of Diffusion

p 250: SPEIGEL, L., [additional comma added]

p 252: of combination with. water -> of combination with water

p 255: upon which the micro-organisms -> microorganisms

p 258: heavy metals; hydro-carbon -> hydrocarbon

p 261: Campferitirin -> Campferitrin

p 261: Certain algae -> algæ

p 261: certain types of algae -> algæ

p 262: mentioned above as "acclimitization"->"acclimatization"

p 270: succinic, 127, 128. -> [period added]

p 270: metapectic -> meta-pectic

p 271: mellisyl -> melissyl

p 271: myriscyl -> myricyl

p 271: Asymetric -> Asymmetric

p 272: Carbon dioxide, 2, 3, 18, 21, 22, 23, -> [comma added]

p 273: Curarin -> Curarine

p 274: Hesperitin, 79, -> [period changed to comma]

p 275: Linayl -> Linalyl

p 275: Leucosine -> Leucosin

p 275: Lupenine -> Lupinine

p 276: Methylethylmallein imide -> Methylethylmalein imide

p 276: Mryosin -> Myrosin

p 276: Oil of lavendar -> lavender

p 276: Oxy-hydroquinone -> Oxyhydroquinone

p 277: Photo-chemical action of light -> Photochemical action of light

p 277: Proteases, 186, 189, 102 -> Proteases, 186, 189, 192

p 278: Sorbose, -> [period changed to comma]