ROOTS.

This subject can be treated more conveniently while the young seedlings

are still growing, because their roots are very suitable for study. It

seems best, therefore, to take it up before examining the buds.

1. _Study of the Roots of Seedlings_.--One or two of the seedlings should

be broken off and the slips put into a glass of water. They will be

studied later. Bean and Sunflower are the best for the purpose.

Begin by telling the pupils to prepare for their first lesson a

description of the roots of their seedlings. Those grown on sponge or

paper will show the development of the root-hairs, while those grown on

sand are better for studying the form of the root. Give them also some

fleshy root to describe, as a carrot, or a radish; and a spray of English

Ivy, as an example of aërial roots.

Throughout these lessons, the method is pursued of giving pupils specimens

to observe and describe before teaching them botanical terms. It is better

for them to name the things they see than to find examples for terms

already learned. In the first case, they feel the difficulty of expressing

themselves and are glad to have the want of exact terms supplied. This

method is discouraging at first, especially to the younger ones; but,

with time and patience, they will gradually become accustomed to describe

whatever they can see. They have, at any rate, used their eyes; and,

though they may not understand the real meaning of anything they have

seen, they are prepared to discuss the subject intelligently when they

come together in the class. If they will first write out their unassisted

impressions and, subsequently, an account of the same thing after they

have had a recitation upon it, they will be sure to gain something in the

power of observation and clear expression. It cannot be too strongly

urged that the number of facts that the children may learn is not of the

slightest consequence, but that the teacher should aim to cultivate the

quick eye, the ready hand, and the clear reason.

The root of the Morning-Glory is _primary_; it is a direct downward growth

from the tip of the caulicle. It is about as thick as the stem, tapers

towards the end, and has short and fibrous branches. In some plants the

root keeps on growing and makes a _tap-root_; in the Bean, it soon becomes

lost in the branches. These are all simple, that is, there is but one

primary root. Sometimes there are several or many, and the root is then

said to be _multiple_. The Pumpkin is an example of this. The root of

the Pea is described in the older editions of Gray's Lessons as being

multiple, but it is generally simple. Indian Corn, also, usually starts

with a single root, but this does not make a tap-root, and is soon

followed by many others from any part of the caulicle, or even from the

stem above, giving it the appearance of having a multiple root.

The root of the Radish is different from any of these; it is _fleshy_.

Often, it tapers suddenly at the bottom into a root like that of

the Morning-Glory with some fibres upon it. It is, in fact, as the

Morning-Glory would be if the main root were to be thickened up by

food being stored in it. It is a primary tap-root. The radish is

_spindle-shaped_, tapering at top and bottom, the carrot is _conical_, the

turnip is called _napiform_; some radishes are shaped like the turnip.

The aërial roots of the English Ivy answer another purpose than that of

giving nourishment to the plant. They are used to support it in climbing.

These are an example of _secondary_ roots, which are roots springing

laterally from any part of the stem. The Sweet Potato has both fleshy and

fibrous roots and forms secondary roots of both kinds every year.[1] Some

of the seedlings will probably show the root-hairs to the naked eye. These

will be noticed hereafter.

[Footnote 1: Gray's Lessons, p. 35, Fig. 86.]

[Illustration: FIG. 11.--1. Tap-root. 2. Multiple root of Pumpkin. 3.

Napiform root of Turnip. 4. Spindle-shaped root of Radish. 5. Conical root

of Carrot. 6. Aërial roots of Ivy.]

It is my experience that pupils always like classifying things under

different heads, and it is a good exercise. The following table may be

made of the roots they have studied, adding other examples. Dr. Gray says

that ordinary roots may be roughly classed into fibrous and fleshy.[1]

Thomé classes them as woody and fleshy.[2]

[Footnote 1: Gray's Lessons, p. 34.]

[Footnote 2: Text-book of Structural and Physiological Botany. Otto Thomé.

Translated and edited by Alfred W. Bennett, New York. John Wiley and Sons.

1877. Page 75.]

ROOTS.

|

------------------------------------------

| |

_Primary_. _Secondary_.

| |

-------------------------------- |

| | |

_Fibrous_. _Fleshy_. Roots of cuttings

| Aërial roots.

------------------- Sweet potatoes.[3]

| |

_Simple_. _Multiple_. _Simple_.

Morning Glory. Pumpkin Carrot.

Sunflower. Radish.

Pea. Turnip.

Bean. Beet.

Corn. Corn.

[Footnote 3: The Irish potato will very likely be mentioned as an example

of a fleshy root. The teacher can say that this will be explained later.]

2. _Fleshy Roots_.--The scholars are already familiar with the storing

of food for the seedling in or around the cotyledons, and will readily

understand that these roots are storehouses of food for the plant. The

Turnip, Carrot, and Beet are _biennials_; that is, their growth is

continued through two seasons. In the first year, they make a vigorous

growth of leaves alone, and the surplus food is carried to the root in the

form of a syrup, and there stored, having been changed into starch, or

something very similar. At the end of the first season, the root is filled

with food, prepared for the next year, so that the plant can live on its

reserve fund and devote its whole attention to flowering. These roots

are often good food for animals. There are some plants that store their

surplus food in their roots year after year, using up in each season the

store of the former one, and forming new roots continually. The Sweet

Potato is an example of this class. These are _perennials_. The food in

perennials, however, is usually stored in stems, rather than in roots, as

in trees. _Annuals_ are generally fibrous-rooted, and the plant dies after

its first year. The following experiment will serve as an illustration of

the way in which the food stored in fleshy roots is utilized for growth.

Cut off the tapering end of a carrot and scoop out the inside of the

larger half in the form of a vase, leaving about half of the flesh behind.

Put strings through the upper rim, fill the carrot cup with water, and

hang it up in a sunny window. Keep it constantly full of water. The

leaf-buds below will put forth, and grow into leafy shoots, which, turning

upwards, soon hide the vase in a green circle. This is because the dry,

starchy food stored in the carrot becomes soft and soluble, and the supply

of proper food and the warmth of the room make the leaf-buds able to grow.

It is also a pretty illustration of the way in which stems always grow

upward, even though there is enough light and air for them to grow

straight downwards. Why this is so, we do not know.

3. _Differences between the Stem and the Root.--_Ask the pupils to tell

what differences they have found.

_Stems_. _Roots_.

Ascend into the air. Descend into the ground.

Grow by a succession of similar Grow only from a point

parts, each part when young just behind the tip.

elongating throughout.

Bear organs. Bear no organs.

There are certain exceptions to the statement that roots descend into the

ground; such as aërial roots and parasitic roots. The aërial roots of the

Ivy have been mentioned. Other examples of roots used for climbing are

the Trumpet Creeper _(Tecoma radicans)_, and the Poison Ivy _(Rhus

Toxicodendron)_. Parasitic roots take their food ready-made from the

plants into which they strike. The roots of air-plants, such as certain

orchids, draw their nourishment from the air.

The experiment of marking roots and stem has been already tried, but it

should be repeated. Repetition of experiments is always desirable, as it

fixes his conclusions in the pupil's mind. The stem grows by a succession

of similar parts, _phytomera_, each part, or _phyton_, consisting of node,

internode, and leaf. Thus it follows that stems must bear leaves. The

marked stems of seedlings show greater growth towards the top of the

growing phyton. It is only young stems that elongate throughout. The older

parts of a phyton grow little, and when the internode has attained a

certain length, variable for different stems and different conditions, it

does not elongate at all.

The root, on the contrary, grows only from a point just behind the tip.

The extreme tip consists of a sort of cap of hard tissue, called the

root-cap. Through a simple lens, or sometimes with the naked eye, it can

be distinguished in most of the roots of the seedlings, looking like a

transparent tip. "The root, whatever its origin in any case may be, grows

in length only in one way; namely, at a point just behind its very

tip. This growing point is usually protected by a peculiar cap, which

insinuates its way through the crevices of the soil. If roots should grow

as stems escaping from the bud-state do,--that is, throughout their whole

length--they would speedily become distorted. But, since they grow at the

protected tips, they can make their way through the interstices of soil,

which from its compactness would otherwise forbid their progress."[1]

[Footnote 1: Concerning a few Common Plants, p. 25.]

The third difference is that, while the stem bears leaves, and has buds

normally developed in their axils, roots bear no organs. The stem,

however, especially when wounded, may produce buds anywhere from the

surface of the bark, and these buds are called _adventitious_ buds. In the

same manner, roots occasionally produce buds, which grow up into leafy

shoots, as in the Apple and Poplar.[1]

[Footnote 1: See Gray's Structural Botany, p. 29.]

It should be made perfectly clear that the stem is the axis of the plant,

that is, it bears all the other organs. Roots grow from stems, not steins

from roots, except in certain cases, like that of the Poplar mentioned

above. This was seen in the study of the seedling. The embryo consisted of

stem and leaves, and the roots were produced from the stem as the seedling

grew.

For illustration of this point, the careful watching of the cuttings

placed in water will be very instructive. After a few days, small, hard

lumps begin to appear under the skin of the stem of the broken seedling

Bean. These gradually increase in size until, finally, they rupture the

skin and appear as rootlets. Roots are always thus formed under the outer

tissues of the stem from which they spring, or the root from which they

branch. In the Bean, the roots are in four long rows, quartering the stem.

This is because they are formed in front of the woody bundles of the stem,

which in the seedling Bean are four. In the Sunflower the roots divide the

circumference into six parts. In some of my cuttings of Beans, the stem

cracked in four long lines before the roots had really formed, showing the

parenchyma in small hillocks, so to speak. In these the gradual formation

of the root-cap could be watched throughout, with merely a small lens. I

do not know a better way to impress the nature of the root on the pupil's

mind. These forming roots might also be marked very early, and so be shown

to carry onward their root-cap on the growing-point.

4. _Root-hairs_. These are outgrowths of the epidermis, or skin of the

root, and increase its absorbing power. In most plants they cannot be seen

without the aid of a microscope. Indian Corn and Oats, however, show them

very beautifully, and the scholars have already noticed them in their

seedlings. They are best seen in the seedlings grown on damp sponge. In

those grown in sand, they become so firmly united to the particles of

soil, that they cannot be separated, without tearing the hairs away from

the plant. This will suggest the reason why plants suffer so much from

careless transplanting.

The root-hairs have the power of dissolving mineral matters in the soil

by the action of an acid which they give out. They then absorb these

solutions for the nourishment of the plant. The acid given out was first

thought to be carbonic acid, but now it is supposed by some experimenters

to be acetic acid, by others to vary according to the plant and the time.

The action can be shown by the following experiment, suggested by Sachs.

[Illustration: Fig. 12. I. Seedling of _Sinapis alba_ showing root-hairs.

II. Same, showing how fine particles of sand cling to the root-hairs.

(Sachs.)]

Cover a piece of polished marble with moist sawdust, and plant some seeds

upon it. When the seedlings are somewhat grown, remove the sawdust, and

the rootlets will be found to have left their autographs behind. Wherever

the roots, with their root-hairs have crept, they have eaten into the

marble and left it corroded. The marks will become more distinct if the

marble is rubbed with a little vermilion.

In order that the processes of solution and absorption may take place, it

is necessary that free oxygen should be present. All living things must

have oxygen to breathe, and this gas is as needful for the germination of

seeds, and the action of roots and leaves, as it is for our maintenance of

life. It is hurtful for plants to be kept with too much water about their

roots, because this keeps out the air. This is the reason why house-plants

are injured if they are kept too wet.

A secondary office of root-hairs is to aid the roots of seedlings to enter

the ground, as we have before noticed.

The root-hairs are found only on the young parts of roots. As a root grows

older the root-hairs die, and it becomes of no further use for absorption.

But it is needed now for another purpose, as the support of the growing

plant. In trees, the old roots grow from year to year like stems, and

become large and strong. The extent of the roots corresponds in a general

way to that of the branches, and, as the absorbing parts are the young

rootlets, the rain that drops from the leafy roof falls just where it is

needed by the delicate fibrils in the earth below.[1]

[Footnote 1: Reader in Botany. VI. The Relative Positions of Leaves and

Rootlets.]

5. _Comparison of a Carrot, an Onion, and a Potato_.--It is a good

exercise for a class to take a potato, an onion, and a carrot or radish to

compare, writing out the result of their observations.

The carrot is a fleshy root, as we have already seen. The onion consists

of the fleshy bases of last year's leaves, sheathed by the dried remains

of the leaves of former years, from which all nourishment has been drawn.

The parallel veining of the leaves is distinctly marked. The stem is a

plate at the base, to which these fleshy scales are attached. In the

centre, or in the axils of the scales, the newly-forming bulbs can be

seen, in onions that are sprouting. If possible, compare other bulbs, as

those of Tulip, Hyacinth, or Snowdrop, and the bulb of a Crocus, in which

the fleshy part consists of the thickened base of the stem, and the leaves

are merely dry scales. This is called a _corm_.

The potato is a thickened stem. It shows itself to be a stem, because it

bears organs. The leaves are reduced to little scales (eyelids), in the

axils of which come the buds (eyes). The following delightful experiment

has been recommended to me.

In a growing potato plant, direct upwards one of the low shoots and

surround it with a little cylinder of stiff carpet paper, stuffed with

sphagnum and loam. Cut away the other tuber-disposed shoots as they

appear. The enclosed shoot develops into a tuber which stands more or less

vertical, and the scales become pretty little leaves. Removing the paper,

the tuber and leaves become green, and the latter enlarge a little. A

better illustration of the way in which organs adapt themselves to their

conditions, and of the meaning of morphology, could hardly be found.

_Gray's First Lessons_. Sect. v, 65-88. _How Plants Grow_. Chap. I, 83-90.