Grain of Indian Corn
[Illustration: FIG. 9. 1. Grain of Indian Corn. 2. Vertical section, dividing the embryo,a, caulicle:b, cotyledon;c, plumule. 3. Vertical section, at right angles to the last.]
6.Monocotyledons.—These are more difficult. Perhaps it is not worth while to attempt to make the pupils see the embryo in Wheat and Oats. But the embryo of Indian Corn is larger and can be easily examined after long soaking. Removing the seed-covering, we find the greater part of the seed to be albumen. Closely applied to one side of this, so closely that it is difficult to separate it perfectly, is the single cotyledon. This completely surrounds the plumule and furnishes it with food from the albumen. There is a line down the middle, and, if we carefully bend back the edges of the cotyledon, it splits along this line, showing the plumule and caulicle within. The plumule consists of successive layers of rudimentary leaves, the outer enclosing the rest (Fig. 10, 1,c). The latter is the first leaf and remains undeveloped as a scaly sheath (Fig. 10, 2,c). In Wheat and Oats the cotyledon can be easily seen in the largest seedlings by pulling off the dry husk of the grain. The food will he seen to have been used up.
Germination of Indian corn
[Illustration: FIG. 10. 1. Germination of Indian corn. 2. Same more advanced.a, caulicle;c1, first leaf of the plumule, sheathing the rest;c2, second leaf;c3, third leaf of the plumule;d, roots.]
The series of Corn seedlings, at least, should be drawn as before and the parts marked, this time with their technical terms. The following questions should then be prepared.
CORN.
What are the parts of the seed?
Compare these parts with the Morning-Glory, Sunflower, Bean, and Pea.
Where is the food stored?
How many cotyledons have Corn, Wheat, and Oats?
How many have Bean, Pea, Morning-Glory, and Sunflower?
Compare the veins of the leaves of each class and see what difference you can find.
This will bring up the terms dicotyledon and monocotyledon.Dimeans two,monomeans one. This difference in the veins, netted in the first class, parallel in the second, is characteristic of the classes. Pupils should have specimens of leaves to classify under these two heads. Flowering plants are divided first into these two classes, the Dicotyledons and the Monocotyledons.
If Pine-seeds can be planted, the polycotyledonous embryo can also be studied.
7.Food of seedlings.—The food of the Wheat seedling may be shown in fine flour. [1]"The flour is to be moistened in the hand and kneaded until it becomes a homogeneous mass. Upon this mass pour some pure water and wash out all the white powder until nothing is left except a viscid lump of gluten. This is the part of the crushed wheat-grains which very closely resembles in its composition the flesh of animals. The white powder washed away is nearly pure wheat-starch. Of course the other ingredients, such as the mineral matter and the like, might be referred to, but the starch at least should be shown. When the seed is placed in proper soil, or upon a support where it can receive moisture, and can get at the air and still be warm enough, a part of the starch changes into a sort of gum, like that on postage stamps, and finally becomes a kind of sugar. Upon this sirup the young seedling feeds until it has some good green leaves for work, and as we have seen in the case of some plants it has these very early."
The presence of starch can be shown by testing with a solution of iodine. Starch is turned blue by iodine and may thus be detected in flour, in seeds, in potatoes, etc.
After all this careful experimental work the subject may be studied in the text-book and recited, the recitation constituting a thorough review of the whole.
A charming description of the germination of a seed will be found in the Reader. V. The Birth of Picciola.
Gray's Lessons. Sect. II, 8-14. III.How Plants Grow. Sect. I, 22, 23. II.
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 isprimary; 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 atap-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 bemultiple. 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 isfleshy. 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 isspindle-shaped, tapering at top and bottom, the carrot isconical, the turnip is callednapiform; 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 ofsecondaryroots, 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.
Root shapes
[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]
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 arebiennials; 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 areperennials. The food in perennials, however, is usually stored in stems, rather than in roots, as in trees.Annualsare 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.
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, orphyton, 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]
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 calledadventitiousbuds. In the same manner, roots occasionally produce buds, which grow up into leafy shoots, as in the Apple and Poplar.[1]
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.
Seedling of Sinapis alba
[Illustration: Fig. 12. I. Seedling ofSinapis albashowing 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]
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 acorm.
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.
1. There is an astonishing amount to be learned from naked branches, and, if pursued in the right way, the study will be found exceedingly interesting. Professor Beal, in his pamphlet on the New Botany,[1] says:—
"Before the first lesson, each pupil is furnished or told where to procure some specimen for study. If it is winter, and flowers or growing plants cannot be had, give each a branch of a tree or shrub; this branch may be two feet long. The examination of these is made during the usual time for preparing lessons, and not while the class is before the teacher. For the first recitation each is to tell what he has discovered. The specimens are not in sight during the recitation. In learning the lesson, books are not used; for, if they are used, no books will contain a quarter of what the pupil may see for himself. If there is time, each member of the class is allowed a chance to mention anything not named by any of the rest. The teacher may suggest a few other points for study. The pupils are not told what they can see for themselves. An effort is made to keep them working after something which they have not yet discovered. If two members disagree on any point, on the next day, after further study, they are requested to bring in all the proofs they can to sustain their different conclusions. For a second lesson, the students review the first lesson, and report on a branch of a tree of another species which they have studied as before. Now they notice any point of difference or of similarity. In like manner new branches are studied and new comparisons made. For this purpose, naked branches of our species of elms, maples, ashes, oaks, basswood, beech, poplars, willows, walnut, butternut, hawthorns, cherries, and in fact any of our native or exotic trees or shrubs are suitable. A comparison of the branches of any of the evergreens is interesting and profitable. Discoveries, very unexpected, are almost sure to reward a patient study of these objects. The teacher must not think time is wasted. No real progress can be made, till the pupils begin to learn to see; and to learn to see they must keep trying to form the habit from the very first; and to form the habit they should make the study of specimens the main feature in the course of training."
HORSECHESTNUT (Æsculus Hippocastanum).
We will begin with the study of a branch of Horsechestnut.[1] The pupils should examine and describe their specimens before discussing them in the class-room. They will need some directions and hints, however, to enable them to work to any advantage. Tell them to open both large and small buds. It is not advisable to study the Horsechestnut bud by cutting sections, as the wool is so dense that the arrangement cannot be seen in this way. The scales should be removed with a knife, one by one, and the number, texture, etc., noted. The leaves and flower-cluster will remain uncovered and will be easy to examine. The gum may be first removed by pressing the bud in a bit of paper. The scholars should study carefully the markings on the stem, in order to explain, if possible, what has caused them. The best way to make clear the meaning of the scars is to show them the relation of the bud to the branch. They must define a bud. Ask them what the bud would have become the next season, if it had been allowed to develop. It would have been a branch, or a part of one. A bud, then, is an undeveloped branch. They can always work out this definition for themselves. Conversely, a branch is a developed bud, or series of buds, and every mark on the branch must correspond to something in the bud. Let them examine the specimens with this idea clearly before their minds. The lesson to prepare should be to write out all they can observe and to make careful drawings of their specimens. Ask them to find a way, if possible, to tell the age of the branch.
At the recitation, the papers can be read and the points mentioned thoroughly discussed. This will take two lesson-hours, probably, and the drawing may be left, if desired, as the exercise to prepare for the second recitation.
[1]The buds of Horsechestnut contain the plan of the whole growth of the next season. They are scaly and covered, especially towards the apex, with a sticky varnish. The scales are opposite, like the leaves. The outer pairs are wholly brown and leathery, the succeeding ones tipped with brown, wherever exposed, so that the whole bud is covered with a thick coat. The inner scales are green and delicate, and somewhat woolly, especially along the lapping edges. There are about seven pairs of scales. The larger terminal buds have a flower-cluster in the centre, and generally two pairs of leaves; the small buds contain leaves alone, two or three pairs of them. The leaves are densely covered with white wool, to protect them from the sudden changes of winter. The use of the gum is to ward off moisture. The flower-cluster is woolly also.
The scars on the stem are of three kinds, leaf, bud-scale, and flower-cluster scars. The pupils should notice that the buds are always just above the large triangular scars. If they are still in doubt as to the cause of these marks, show them some house-plant with well-developed buds in the axils of the leaves, and ask them to compare the position of these buds with their branches. The buds that spring from the inner angle of the leaf with the stem areaxillarybuds; those that crown the stems areterminal. Since a bud is an undeveloped branch, terminal buds carry, on the axis which they crown, axillary buds give rise to side-shoots. The leaf-scars show the leaf-arrangement and the number of leaves each year. The leaves are opposite and each pair stands over the intervals of the pair below. The same is observed to be true of the scales and leaves of the bud.[1] All these points should be brought out by the actual observation of the specimens by the pupils, with only such hints from the teacher as may be needed to direct their attention aright. The dots on the leaf-scar are the ends of woody bundles (fibro-vascular bundles) which, in autumn, separated from the leaf. By counting these we can tell how many leaflets there were in the leaf, three, five, seven, nine, or occasionally six or eight.
Horsechestnut
[Illustration: FIG. 13.—Horsechestnut. I. Branch in winter state:a, leaf-scars;b, bud-scars;c, flower-scars. 2. An expanding leaf-bud. 3. Same, more advanced.]
The Bud Scale-Scars. These are rings left by the scales of the bud and may be seen in many branches. They are well seen in Horsechestnut. If the pupils have failed to observe that these rings show the position of former buds and mark the growth of successive years, this point must be brought out by skilful questioning. There is a difference in the color of the more recent shoots, and a pupil, when asked how much of his branch grew the preceding season, will be able to answer by observing the change in color. Make him see that this change corresponds with the rings, and he will understand how to tell every year's growth. Then ask what would make the rings in a branch produced from one of his buds, and he can hardly fail to see that the scales would make them. When the scholars understand that the rings mark the year's growth, they can count them and ascertain the age of each branch. The same should be done with each side-shoot. Usually the numbers will be found to agree; that is, all the buds will have the same number of rings between them and the cut end of the branch, but occasionally a bud will remain latent for one or several seasons and then begin its growth, in which case the numbers will not agree; the difference will be the number of years it remained latent. There are always many buds that are not developed. "The undeveloped buds do not necessarily perish, but are ready to be called into action in case the others are checked. When the stronger buds are destroyed, some that would else remain dormant develop in their stead, incited by the abundance of nourishment which the former would have monopolized. In this manner our trees are soon reclothed with verdure, after their tender foliage and branches have been killed by a late vernal frost, or consumed by insects. And buds which have remained latent for several years occasionally shoot forth into branches from the sides of old stems, especially in certain trees."[1]
The pupils can measure the distance between each set of rings on the main stem, to see on what years it grew best.
The Flower-Cluster Scars. These are the round, somewhat concave, scars, found terminating the stem where forking occurs, or seemingly in the axils of branches, on account of one of the forking branches growing more rapidly and stoutly than the other and thus taking the place of the main stem, so that this is apparently continued without interruption. If the pupils have not understood the cause of the flower-cluster scars, show them their position in shoots where they are plainly on the summit of the stem, and tell them to compare this with the arrangement of a large bud. The flower-cluster terminates the axis in the bud, and this scar terminates a branch. When the terminal bud is thus prevented from continuing its growth, the nearest axillary buds are developed.[1] One shoot usually gets the start, and becomes so much stronger that it throws the other to one side. The tendency of the Horsechestnut to have its growth carried on by the terminal buds is so strong that I almost feel inclined to say that vigorous branches are never formed from axillary buds, in old trees, except where the terminal bud has been prevented from continuing the branch. This tendency gives to the tree its characteristic size of trunk and branches, and lack of delicate spray. On looking closely at the branches also, they will be seen to be quite irregular, wherever there has been a flower-cluster swerving to one side or the other.
There is one thing more the pupils may have noticed. The small round dots all over the young stem, which become long rifts in the older parts, are breaks in the epidermis, or skin of the stem, through which the inner layers of bark protrude. They are called lenticels. They provide a passage for gases in and out of the stem. In some trees, as the Birch, they are very noticeable.
After discussing the subject thoroughly in the class-room, the pupils should rewrite their papers, and finally answer the following questions, as a species of review. I have thus spent three recitations on the Horsechestnut. The work is all so new, and, if properly presented, so interesting, that a good deal of time is required to exhaust its possibilities of instruction. If the teacher finds his scholars wearying, however, he can leave as many of the details as he pleases to be treated in connection with other branches.
QUESTIONS ON THE HORSECHESTNUT.
How many scales are there in the buds you have examined?
How are they arranged?
How many leaves are there in the buds?
How are they arranged?
Where does the flower-cluster come in the bud?
Do all the buds contain flower-clusters?
What is the use of the wool and the gum?
Where do the buds come on the stem?
Which are the strongest?
How are the leaves arranged on the stem?
Do the pairs stand directly over each other?
What are the dots on the leaf-scars?
How old is your branch?
How old is each twig?
Which years were the best for growth?
Where were the former flower-clusters?
What happens when a branch is stopped in its growth by flowering?
What effect does this have on the appearance of the tree?
In some parts of the country the Horsechestnut is not so commonly planted as in New England. In the southern states the Magnolia may be used in its stead, but it is not nearly so simple an example of the main points to be observed.[1]
MAGNOLIA UMBRELLA.
The bud may be examined by removing the scales with a knife, as in Horsechestnut, and also by cutting sections. The outer scales enfold the whole bud, and each succeeding pair cover all within. They are joined, and it is frequently difficult to tell where the suture is, though it can generally be traced at the apex of the bud. On the back is a thick stalk, which is the base of the leaf-stalk. Remove the scales by cutting carefully through a single pair, opposite the leaf-stalk, and peeling them off. The scales are modified stipules, instead of leaf-stalks, as in Horsechestnut. The outer pair are brown and thick, the inner green, and becoming more delicate and crumpled as we proceed toward the centre of the bud. The leaves begin with the second or third pair of scales. The first one or two are imperfect, being small, brown, and dry. The leaves grow larger towards the centre of the bud. They are covered with short, silky hairs, and are folded lengthwise, with the inner surface within (conduplicate). In the specimens I have examined I do not see much difference in size between the buds with flowers and those without. In every bud examined which contained a flower, there was an axillary bud in the axil of the last, or next to the last, leaf. This bud is to continue the interrupted branch in the same way as in Horsechestnut.
There are from six to ten good leaves, in the buds that I have seen. Those without flowers contain more leaves, as in Horsechestnut. In the centre of these buds the leaves are small and undeveloped. The flower is very easy to examine, the floral envelopes, stamens and pistils, being plainly discernible. The bud may also be studied in cross-section. This shows the whole arrangement. The plan is not so simple as in Horsechestnut, where the leaves are opposite. The subject of leaf-arrangement should be passed over until phyllotaxy is taken up.
The scars on the stem differ from Horsechestnut in having no distinct bands of rings. The scales, being stipules, leave a line on each side of the leaf-scar, and these are separated by the growth of the internodes. In the Beech, the scales are also stipules; but, whereas in the Magnolia there are only one or two abortive leaves, in the Beech there are eight or nine pairs of stipules without any leaves at all. The rings thus become separated in Magnolia, while in the Beech the first internodes are not developed, leaving a distinct band of rings, to mark the season's growth. The Magnolia is therefore less desirable to begin upon. The branches are swollen at the beginning of a new growth, and have a number of leaf-scars crowded closely together. The leaf-scars are roundish, the lower line more curved. They have many dots on them. From each leaf-scar runs an irregular line around the stem. This has been left by the stipules.
The flower-scar is on the summit of the axis, and often apparently in the axil of a branch, as in Horsechestnut. Sometimes the nearest axillary bud is developed; sometimes there are two, when the branch forks. The axillary buds seldom grow unless the terminal bud is interrupted. The tree therefore has no fine spray.
LILAC(Syringa vulgaris).
Ask the scholars to write a description of their branches and to compare them with Horsechestnut. These papers should be prepared before coming into the class, as before.
The buds are four-sided. The scales and leaves are opposite, as in Horsechestnut. The outer pair sometimes have buds in their axils. Remove the scales one by one with a knife, or better, with a stout needle. The scales gradually become thinner as we proceed, and pass into leaves, so that we cannot tell where the scales end and leaves begin. After about six pairs are removed, we come, in the larger buds, to leaves with axillary flower-clusters. The leaves grow smaller and the flower-clusters larger till we come to the centre, where the axis is terminated by a flower-cluster. There is a great difference in the buds on different bushes and on shoots of the same bush, some being large, green, and easy to examine, others small, hard, and dark-colored. It is better, of course, to select as soft and large buds as possible for examination.
Lilac
[Illustration: FIG. 14.—Lilac. I. Branch in winter state:a, leaf-scar;b, bud-scar (reduced). 2. Same, less reduced. 3. Branch, with leaf-buds expanded. 4. Series in a single bud, showing the gradual transition from scales to leaves.]
That the scales are modified leaves is plainly shown by the gradual transition they undergo, and also by the fact that buds are developed in their axils. If any of these can be shown to the pupils, remind them of the experiment where the top of a seedling Pea was cut off and buds forced to develop in the axils of the lower scales.[1] The transition from scales to leaves can be well studied by bringing branches into the house, where they will develop in water, and towards spring may even be made to blossom. Cherry, Apple, Forsythia, and other blossoming trees and shrubs can be thus forced to bloom. Place the branches in hot water, and cut off a little of their ends under water. If the water is changed every day, and the glass kept near the register or stove, they will blossom out very quickly. These expanded shoots may be compared with the buds. The number of leaves in the bud varies.
The leaf-scars of Lilac are horseshoe-shaped and somewhat swollen. It can often be plainly seen that the outer tissue of the stem runs up into the scar. It looks as if there were a layer of bark, ending with the scar, fastened over each side of the stem. These apparent layers alternate as well as the scars. The epidermis, or skin of the leaves, is in fact always continuous with that of the stem. There are no dots on the leaf-scars.
The rings are not nearly so noticeable as in Horsechestnut, but they can be counted for some years back.
The flower-cluster can often be traced by a dried bit of stem remaining on the branch.
The terminal bud in the Lilac does not usually develop, and the two uppermost axillary buds take its place, giving to the shrub the forked character of its branching. In all these bud studies, the pupil should finish by showing how the arrangement of the buds determines the growth of the branches.
QUESTIONS ON THE LILAC.
How do the scales differ from those of Horsechestnut?
How many scales and leaves are there?
How are they arranged?
Where does the flower-cluster come in the bud?
Do all the buds contain flower-clusters?
How does the arrangement of leaves and flower-clusters differ from that of Horsechestnut?
How old is your branch?
Which buds develop most frequently?
How does this affect the appearance of the shrub?
COPPER BEECH (Fagus sylvatica, var. purpurea).
The buds are long and tapering, the scales thin and scarious, the outer naked, the inner with long, silky hairs. Remove the scales one by one, as in Lilac. The outer four or six pairs are so minute that the arrangement is not very clear, but as we proceed we perceive that the scales are in alternate pairs, as in Horsechestnut; that is, that two scales are exactly on the same plane. But we have learned in the Lilac that the scales are modified leaves, and follow the leaf-arrangement of the species. The Beech is alternate-leaved, and we should therefore expect the scales to alternate. The explanation is found as we go on removing the scales. At the eighth or ninth pair we come upon a tiny, silky leaf, directly between the pair of scales, and, removing these, another larger leaf, opposite the first but higher up on the rudimentary stem, and so on, with the rest of the bud. There are five or more leaves, each placed between a pair of scales. Our knowledge of the parts of a leaf shows us at once that the scales must be modified stipules, and that therefore they must be in pairs.[1] Other examples of scales homologous with stipules are the American Elm, Tulip-tree, Poplar and Magnolia. The leaves are plaited on the veins and covered with long, silky hairs. The venation is very distinct. The outer leaves are smaller and, on examining the branch, it will be seen that their internodes do not make so large a growth as the leaves in the centre of the bud.