fundamentally peculiar to the life of organisms? Does the
capacity of the organism thus to adjust itself to its
environment involve factors not found in the operations of
inorganic nature? Our answers will be determined essentially by
the nature of our interest in the organism--whether we regard
its existence as the END or merely an incidental EFFECT of its
activities. The first alternative is compatible with
thoroughgoing vitalism. The second, emphasizing the nature of
the processes rather than their usefulness to the organism,
relieves biology of the embarrassments of vitalistic
speculation, and allies it at the same time more intimately
than ever with physics and chemistry. This alliance promises so
well for the analysis of adaptations, as to demand our serious
attention.
Physiologically, the living organism may be thought of as a
physico-chemical system of great complexity and peculiar
composition which varies from organism to organism and from
part to part. Life itself may be defined as a group of
characteristic activities dependent upon the transformations in
this system under appropriate conditions. According to this
definition, life is determined not only by the physical and
chemical attributes of the system, but by the fitness of its
environment, which Henderson has recently done the important
service of emphasizing.[1] Relatively trifling changes in the
environment suffice to render it unfit, however, that is, to
modify it beyond the limits of an organism's adaptability. The
environmental limits are narrow, then, within which the
transformations of the organic system can take place that are
associated with adaptive reactions. The conditions within these
limits are, further, peculiarly favorable for just such
transformations in just such physico-chemical systems.
[1] "The Fitness of the Environment."
The essential characteristic of the adaptive reaction appears
to be that the organism concerned responds to changing
conditions without losing certain attributes of behavior by
which we recognize organisms in general and by which that
organism is recognized in particular. It exhibits stability in
the midst of change; it retains its identity. But this
stability, let us repeat, is the stability of a certain type of
physico-chemical system, with respect to certain characters
only, and exhibited under certain circumscribed conditions. In
so far as the problem of adaptation is thus restricted in its
application, it remains a question of standards, a taxonomic
convenience, a problem of the organism by definition only,
empty of fundamental significance.
It is to be expected that systems differing widely in
composition and structure will differ in their responses to
given conditions. This will be true whether the systems
compared thus are organic, or inorganic, or representative of
both groups. The compounds of carbon, of which living substance
is so characteristically composed, exhibit properties and
reactions that distinguish them at once in many respects from
the compounds of lead or sulphur. They also differ widely among
themselves; compare, in this connection, serum albumen, acetic
acid, cane sugar, urea. No vitalistic factor is needed for the
interpretation of divergencies of this kind. But there are many
significant similarities between organisms and inorganic
systems as well. These are so frequently overlooked that it
will now be desirable to consider a few illustrative cases. For
the sake of brevity, they have been selected as representative
of but two types of adaptation commonly known under the names
of ACCLIMATIZATION and REGULATION.
Let us first consider the case of organisms which become
acclimatized by slow degrees to new conditions that, suddenly
imposed, would produce fatal results. Hydra is an organism
which becomes thus acclimatized finally to solutions of
strychnine too strong to be endured at first. Outwardly it
appears to suffer in the process no obvious modifications. Yet
modifications of a physiological order take place, as is shown,
first, by the necessary deliberation of the acclimatization,
second, by the death of the organism if transferred abruptly
back to its original environment.
In other forms the structural changes accompanying
acclimatization may be far more conspicuous. For example, the
aerial leaves of Limnophila heterophylla are dentate, while
those grown under water are excessively divided. Again, the
helmets and caudal spines of Hyalodaphnia vary greatly in
length with the seasonal temperature.
In these and the large number of similar cases that might be
cited, stability of the physiological system under changed
conditions is only obtained by changes in the system itself
which are often exhibited by striking structural modifications.
Compare with such phenomena of acclimatization the responses of
sulphur, tin, liquid crystals and iron alloys to changes of
temperature. The rhombic crystals that characterize sulphur at
ordinary temperatures and pressures, give place to monoclinic
crystals at 95.5 degrees C. Sulphur thus exists with two
crystalline forms whose stability depends directly upon the
temperature.
Similarly, tin exists under two stable forms, white and gray,
the one above, the other below the transitional point, which
is, in this case, 18 degrees C. At this temperature white tin
is in a metastable condition, and transforms into the gray
variety. The transformation goes on, then, at ordinary
temperatures, but, fortunately for us as users of tin
implements, very slowly. Its velocity can be increased,
however, by lowering the temperature, on which, then, not only
the transformation itself, but its rate depends.
In this connection may be mentioned cholesteryl acetate and
benzoate and other substances which possess two crystalline
phases, one of which is liquid, unlike other liquids, however,
in being anisotropic. As in the preceding cases, these phases
are expressions of equilibrium at different temperatures.
Especially instructive facts are afforded by the alloys of iron
and carbon. Iron, or ferrite, exists under three forms: as
alpha ferrite below 760 degrees, as beta ferrite between 760
degrees and 900 degrees, and as gamma ferrite above 900
degrees. Only the last is able to hold carbon in solid
solution. The alloys of iron and carbon exist under several
forms. Pearlite is a heterogeneous mixture containing 0.8 per
cent. carbon. When heated to 670 degrees, it becomes
homogeneous, an amount of carbon up to two per cent. dissolves
in the iron, and hard steel or martensite is formed. In
appearance, however, the two forms are so nearly identical as
to be discriminated only by careful microscopical examination.
Cementite is a definite compound of iron and carbon represented
by the formula Fe<3 subscript>C.
When cooled slowly below 670 degrees, martensite yields a
heterogeneous mixture of pearlite and ferrite (or cementite, if
the original mixture contained between 0.8 per cent. and two
per cent. of carbon). Soft steels and wrought iron are thus
obtained. When cooled rapidly, however, as in the tempering of
steel, martensite remains a homogeneous solid solution, or hard
steel.
One can not fail to notice the remarkable parallel between
these facts and the behavior of Hydra in the presence of
strychnine. In both cases new positions of stability are
reached by modifying the original conditions of stability; and
in both, the old positions of stability are regained only by
returns to the original conditions of stability so gradual as
to afford time sufficient for the necessary transformations in
the systems themselves.
The forms which both organic and inorganic systems assume thus
appear to be functions of the conditions in which they exist.
The fact that Hydra is able to regain a position of stability
from which it had been displaced connects the behavior of this
organism not only with the physical phenomena already cited,
but still more intimately with the large class of chemical
reactions which are similarly characterized by equilibrium and
reversibility. Such reactions do not proceed to completion,
which is probably always the case wherever the mixture of the
systems under transformation is homogeneous, as in the case of
solutions. They occur widely among carbon compounds. The
following typical case will suffice to indicate their essential
characteristics.
When ethyl alcohol and acetic acid are mixed, a reaction ensues
which yields ethyl acetate and water. But ethyl acetate and
water react together also, yielding ethyl alcohol and acetic
acid. This second reaction, in a direction opposite to the
first, proceeds in the beginning more slowly also. There comes
a time, however, when the speeds of the two reactions are
equal. A position of equilibrium or apparent rest is thus
reached, which persists as long as the relative proportions of
the component substances remain unchanged.
A great many reversible reactions are made possible by enzymes.
In the presence of diastase, glucose yields glycogen and water,
which, reacting together in the opposite direction, yield
glucose again. In the presence of emulsin, amygdalin is
decomposed into glucose, hydrocyanic acid and benzoic aldehyde,
and reformed from them. Similarly in the presence of lipase,
esters are reformed from alcohols and fatty acids, their
decomposition products.
With the introduction of enzymes, certain complications ensue.
Though it has been shown that lipase acts as a true catalyser,
this may not hold for all, especially for proteolytic, enzymes.
That reversible reactions actually occur in proteids, however,
accompanied as they are in some cases at least by certain
displacements of the position of equilibrium, there appears to
be no question.[2]
[2] Robertson, Univ. Calif. Publ. Physiol., 3, 1909, p. 115.
These examples are but suggestions of the many reversible
reactions that have now been observed among the compounds of
carbon. That they have peculiar significance for the present
discussion resides in the fact that living substance is
composed of carbon compounds, so many and in such exceedingly
complex relations as to present endless possibilities for
shifting equilibria and the physical and chemical adjustments
resulting therefrom.
With these facts in mind we may now turn from the consideration
of acclimatization to a brief discussion of certain phenomena
of regulation--adaptive reactions that are especially
conspicuous in the growth and development of organisms, but
separated by no sharp dividing line from adaptive reactions of
the other type.
When a fragment of an organism transforms, under appropriate
conditions, into a typical individual, the process includes
degenerative aa well as regenerative phases. There is always
some simplification of the structures present, whose character
and amount is determined by the degree of specialization which
has been attained. The smaller the piece, within certain
limits, and the younger physiologically, the more nearly does
it return to embryonic conditions, a fact which can be studied
admirably in the hydroid Corymorpha. In some cases the
simplification is accomplished by abrupt sacrifice of highly
specialized parts, as in Corymorpha, when in a process of
simplification connected with acclimatization to aquarium
conditions, the large tentacles of well-grown specimens fall
away completely from their bases. In other hydroids (e. g.,
Campanularia) the tentacles may be completely absorbed into the
body of the hydranth from which they originally sprang. Among
tissue cells degenerative changes may be abrupt, as in the
sacrifice of the highly specialized fibrillae in muscle cells;
or they may be very gradual, as in the transformation of cells
of one sort into another that occurs in the regeneration of
tentacles in Tubularia.
An interesting case of absorption of parts came to my notice
while studying the larvae of the pennatulid coral Renilla some
fifteen years ago. As will be remembered, Renilla possesses
eight tentacles with numerous processes pinnately arranged.
During a period of enforced starvation, these pinnae were
gradually absorbed, and the tentacles shortened, from tip to
base. With the advent of food--in the form of annelid eggs--the
reverse of these events took place. The tentacles lengthened
and the pinnae reappeared, the larvae assuming their normal
aspect.
It appears, then, that in some circumstances at least, the
process of simplification may resemble very nearly, even in
details, a reversal of the process of differentiation. That one
is actually in every respect the reverse of the other is
undoubtedly not true. This, however, is not to be wondered at.
Mechanical inhibitions that are so conspicuous in some cases
(e. g., Corymorpha) are to be expected to a certain degree in
all. The regenerative process itself depends upon the
cooperation of many physical and chemical factors, in many and
complex physicochemical systems in varying conditions of
equilibrium. And it is important to note that even the
equilibrium reactions by which a single proteid in the presence
of an enzyme, is made and unmade, do not appear always to
follow identically the same path in opposite directions.[3]
[3] Robertson, vid. sup., p. 269.
Whatever their course in the instances cited and in many
others, reversals in the processes of development do take
place. In perhaps their simplest form these can be seen in egg
cells. The development of a fragment of an egg as a complete
whole involves reversals in the processes of differentiation of
a very subtle order. The fusion of two eggs to one involves
similar readjustments. Such phenomena have been held to be
peculiar to living machines only. Yet it may be pointed out
that there are counterparts of both in the behavior of
so-called liquid crystals. When liquid crystals of
paraazoxyzimtsaure-Athylester are divided, the parts are
smaller in size, but otherwise identical with the parent
crystal in form, structure and optical properties. The fusion
of two crystals of ammonium oleate forming a single crystal of
larger size has also been observed. Though changes in
equilibrium that accompany such behavior of liquid crystals are
undoubtedly very much simpler than the changes that accompany
the regulatory processes exhibited by the living egg, the
striking resemblance between the phenomena themselves tempts us
not to magnify the difference.
Further temptation in the same direction is offered by the
recent discovery[4] that the processes of development
stimulated in the eggs of the sea urchin Arbacia by butyric
acid or weak bases, and evidenced by the formation of the
fertilization membrane, is reversible. When such eggs are
treated with a weak solution of sodium cyanide or chloral
hydrate, they return to the resting condition. Upon
fertilization with spermatozoa, in normal sea water, they
proceed again to develop.
[4] Loeb, Arch. f. Entw., 28, 1914, p. 277.
The facts that have now been briefly summarized have been
selected to emphasize the growing intimacy between the
biological and the inorganic sciences. No harm can conceivably
come from it. On the contrary, there is every reason to be
hopeful that the investigation of biological problems in the
impersonal spirit that has long distinguished the maturer
sciences of physics and chemistry will continue to develop a
better control and fuller understanding of the processes in
living organisms, of which the phenomena of variation in
general, and of adaptation in particular, are but incidental
effects.
WHY CERTAIN PLANTS ARE ACRID
BY PROFESSOR WILLIAM B. LAZENBY
OHIO STATE UNIVERSITY
EVER since my first lessons in botany, the characteristic
qualities and properties of plants have given me much thought.
Why certain plants produced aromatic oils and ethers, while
others growing under the same conditions produced special acids
or alkaloids, was a subject of endless speculation.
The pleasing aroma of the bark of various trees and shrubs, the
spicy qualities of the foliage and seeds of other plants; the
intense acridity; the bitterness; the narcotic, the poisonous
principle in woody and herbaceous species; all were intensely
interesting.
This interest was biological rather than chemical. I cared less
for the ultimate composition of the oils, acids, alkalis, etc.,
than I did for their use or office in the plant economy, and
their effect upon those who might use them.
Perhaps no one plant interested me more from this point of
view, than the well-known Indian turnip (Arisoema triphyllum).
As a boy I was well acquainted with the signally acrid quality
of this plant; I was well aware of its effect when chewed, yet
I was irresistibly drawn to taste it again and again. It was
ever a painful experience, and I suffered the full penalty of
my rashness. As an awn from a bearded head of barley will win
its disputed way up one's sleeve, and gain a point in advance
despite all effort to stop or expel it, so did every
resolution, every reflection, counteract the very purpose it
was summoned to oppose, and to my sorrow I would taste the
drastic, turnip-shaped corm wherever opportunity occurred.
It is a well-known fact that the liquid content of the cells of
plants contain numerous inorganic substances in solution. Among
these, not considering oxygen, hydrogen, nitrogen and carbon
dioxide, there are the salts of calcium, magnesium, potassium,
iron, sulphur and phosphorus. The above substances are found in
the cells of every living plant. Other substances like salts of
sodium and silica are also found, but these are not regarded as
essential to the life and growth of plants. They appear to be
present because the plant has not the power to reject them.
Many of the substances named above, are found deposited either
in an amorphous or crystalline form in the substance of the
cell wall. In addition to this, crystals of mineral matter,
having various shapes and sizes, are often found in the
interior of cells. The most common of these interior cell
crystals are those composed of calcium oxalate and calcium
carbonate. Others composed of calcium phosphate, calcium
sulphate and silica are sometimes found. These crystals may
occur singly or in clusters of greater or less size. In shape
they are prismatic or needle-like.
It is not the object of this paper to treat of plant crystals
in general, but to consider the peculiar effect produced by
certain forms when found in some well-known plants.
The extreme acridity or intense pungency of the bulbs, stems,
leaves and fruit of various species of the Araceae or Arum
family, was recognized centuries ago. The cause of this
characteristic property or quality was, until a comparatively
recent date, not definitely determined.
As far as I am aware the first scientific investigation of this
subject was made by the writer. At a meeting of the American
Association for the Advancement of Science held at Indianapolis
in 1890, some studies and experiments were reported in a short
paper entitled "Notes upon the Crystals in certain species of
the Arum Family."
This paper expressed the belief that the acridity of the Indian
turnip and other plants belonging to the same family, was due
to the presence of needle-shaped crystals or raphides found in
the cells of these plants. This conclusion was not accepted by
Professor T. J. Burrill, of the University of Illinois, nor by
other eminent botanists who were present and took part in the
discussion that followed the reading of the paper.
The opposition was based mainly on the well-known fact that
many other plants like the grape, rhubarb, fuchsia, spiderwort,
etc., are not at all, or but slightly acrid, although the
raphides are as abundant in them as in the Indian turnip and
its allies.
Up to this time the United States Dispensatory and other works
on pharmacy, ascribed the following rather indefinite cause for
the acridity of the Indian turnip. It was said to be due to an
acrid, extremely volatile principle. This principle was
insoluble in water and alcohol, but soluble in ether. It was
dissipated both by heating and drying, and by this means the
acridity is destroyed. There was no opinion given as to the
real nature of this so-called principle.
More recently it has been intimated that the acridity may be
due to some ferment or enzyme, which has been derived in part
from the self-decomposition of protoplasm and in part by the
process of oxidation and reduction.
Here the question appeared to rest. At all events I was unable
to glean any further knowledge from the sources at my command.
Some time later the subject was taken up in a more
comprehensive manner and the following report is the first
detailed description of an investigation that has occupied more
or less of my leisure for some years.
A dozen or more species of plants have been used for
examination and study. Among these were:
Indian turnip (Arisoema triphyllum).
Green dragon (Arisoema dracontium).
Sweet-flag (Acorus).
Skunk cabbage (Spathyema).
Calla (Richardia).
Caladium (Caladium).
Calocasia (Calocasia).
Phyllodendron (Phyllodendron).
Fuchsia (Fuchsia).
Wandering Jew (Tradescantia).
Rhubarb (Rheum).
Grape (Vitis).
Onion (Allium).
Horse-radish (Armoracia).
Most of the plants selected were known to have crystals in
certain parts. Some of them were known to be intensely acrid.
In these the acridity was in every instance proportional to the
number of crystals.
The following order of study was pursued and the results of
each step noted. Only the more salient points of the methods
employed and the conclusions reached are presented.
1. The Character of the Taste Itself.--It was readily noted
that the sensation produced by chewing the various acrid plants
was quite different. For example, the Indian turnip and its
close allies do not give the immediate taste or effect that
follows a similar testing of the onion or horse-radish. When
the acridity of the former is perceived the sensation is more
prickling than acrid.
The effect produced is more like the pricking of numerous
needles. It is felt not only upon the tongue and palate, but
wherever the part tasted comes into contact with the lips, roof
of mouth or any delicate membrane. It is not perceived where
this contact does not occur.
The acridity of the onion and horse-radish is perceived at once
and often affects other parts than those with which it comes
into direct contact.
2. The Acrid Principle Is Not Always Volatile.--This is shown
by the fact that large quantities of the mashed or finely
grated corms of the Indian turnip and allied species, produced
no irritation of the eyes or nose even when these organs were
brought into close contact with the freshly pulverized
material. This certainly is in marked contrast with the effect
produced by freshly grated horse-radish, peeled onions, crushed
mustard seed when the same test is applied.
It seems fair to assume that in the latter case some principle
that is volatile at ordinary air temperatures is present. The
assumption that such principle is present in the former has no
room.
In order to test this matter further a considerable quantity of
the juice of the Indian turnip was subjected to careful
distillation, with the result that no volatile principle or
substance of any kind was found.
Various extractive processes were tried by using hot and cold
water; alcohol, chloroform, benzene, etc. These failed in every
instance to remove any substance that had a taste or effect
anything like that found in the fresh Indian turnip.
3. The Acrid Principle Is Not Soluble in Ether.--Inasmuch as
various works on pharmacy made the claim that the active or
acrid principle of the plants in question was soluble in ether,
this was the next subject for investigation. The juice was
expressed from a considerable quantity of the mashed Indian
turnip. This juice was clear and by test was found to possess
the same acrid property as the unmashed corms.