-the oak which was to grow from it, and all the acorn seeds which it was to produce; and in those acorn seeds all the vast forests of oak that have since covered the earth? and that in a single grain of wheat he folded up, in miniature,1 the myriads of wheat plants which man has gathered in all succeeding harvests?

4.

"Lo! in each seed, within its slender rind,"

Life's golden threads in endless circles wind-
Maze' within maze the lucid webs are roll'd,
And, as they burst, the living flame unfold.
The pulpy acorn, ere it swells, contains
The oak's vast branches in its milky veins;
Grain within grain successive harvests dwell,
And boundless forests slumber in a shell."

5. As cell life is the beginning of the life of plants, even in the seeds, so the entire growth of plants is but a continuation of the same process-consisting of millions upon millions of little cells heaped together-forming alike the massive trunk of the oak, and the finest down upon the tiny leaf. When we consider the exceeding minuteness of these cells in some plants, and that some stems shoot up three or four inches in a day, we can form some idea of the wonderful rapidity of cell growth. It is supposed that the century plant, a short time before blooming, increases at the rate of over twenty. thousand millions of cells in a day!

6. Thus, knowing how all vegetables grow, we can better understand the nature of such curious plants as mould, mildew, and yeast, which, having neither stems nor leaves, consist wholly either of a single cell, or of clusters of little cells adhering together. Yeast, which is put into the dough of bread to make it light, consists of little cell plants so exceedingly small that a cubic inch of yeast is said to contain more than eleven hundred millions of them. As the yeast plant grows rapidly in the dough, spreading all through it, and forming its living cells in countless numbers, it gives off little bubbles of gas, which puff up the dough, and thus "leaven the whole lump."

7. Strange though it may seem, yet all animal growth is the growth of cells also, the same as in vegetables. The

muscles, the bones, the nerves, the hair, the nails, consist of cells. The smallest muscular fibre that the microscope can detect is made up of a row of little cells, much like a string of beads. In shape and mode of growth the animal cells are in all respects like the vegetable; but the substances of which they are composed are different.*

8. In very young plants, and also in the lower grades of vegetable life, such as the mushrooms and the mosses, the walls of the cells are very thin; and these are what are called cellular plants. These cells, when first formed, are eggshaped, or globular, and filled with a liquid substance; but when numbers of them are pressed together in the growing plant they assume various forms, as may be seen by examining thin slices of the pith of different kinds of wood with a microscope. (Fig. 3.)

9. The cells are usually soft; but sometimes they are so filled up and pressed together that they become very hard, as in thorns, prickles, and the shells or coverings of nuts. Potatoes, turnips, and other vegetables are made palatable and digestible by breaking up their cells, containing starch and sugar, in the process of boiling or steaming.

10. Some of the cells, at an early stage of their growth, lengthen into the form of short tubes, and thicken their walls. These form what is called, from their shape, vascular tissue,10 or woody fibre. Owing to the strength of this tissue, vascular plants grow to a great height, with sufficient firmness to form the ribs of oak that plow the main, or, towering in their native woods like "the mast of some tall admiral," they are

* The cell walls of plants are composed of what is called cěl'-lu-lose; but animal cells are composed of an animal element called prō'-te-ine.

At 8, in Fig. 3, is shown a cluster of highly-magnified cells, of globular shape, as first formed. At 9 is a lengthened cell, the beginning of such as are found in vascular tissueAt 10 and 11 are globular cells assuming angular forms under the influence of pressure.

enabled to withstand the tempest's shock. Vascular tissue is sometimes in the form of spiral fibre, which may be seen surrounding the pith of some plants, where the thread may easily be uncoiled.

11. Through the small tubular wood-cells the sap is carried from the roots to the leaves. Yet these cells, in the young and growing plant, have no openings, and the sap can pass from one to another only by making its way through their thin walls. And so short are the wood-cells generally, that, to rise a foot in such a tree as the basswood, the sap has to pass through the walls of about two thousand of these cells. There are no continuous11 veins, as many suppose, through which the sap of trees rises. Wood-cells in the bark are generally longer than in the central parts; they give great toughness to the inner bark of many plants, and they furnish the invaluable fibres of flax and hemp.

12. In addition to the cells which have been described, there are larger cells called ducts, which are either long single cells overlapping one another, or rows of cells placed end to end. Some of these are so large that they may be seen by the naked eye when cut across, but they are usually much too small for this. There are also, in various plants, canals or cavities formed between or among the cells, and filled with the particular products of the plant, such as milk, oil, turpentine, etc.

13. These various cells constitute the substance or framework of plants, from the mushroom of a night to the oak of centuries. The diversities of appearance which they present, when viewed by the aid of a microscope, enable us to distinguish one kind of vegetable growth from another, as the fibres of flax or linen from cotton, even when twisted and woven together, and thus to detect frauds in the manufacture

of cloths, where the cheaper material of cotton is intermixed with linen. (Fig. 4.) Our obligations to the woody fibre of plants are infinite, for without it we should have neither linen nor cotton cloths, neither sails nor cordage for our ships, nor a door-mat upon which to clean our shoes; without it the books of the present day would have no existence, for the paper upon which they are printed consists of wooden fibre.

14. All plants have a covering called the cuticle; and this, formed of cells also, extends from the lowest root to the topmost twig, spreading over every leaf, and enveloping the whole plant. Yet in one of the great classes of plants, the exogenous, or outward-growing, this covering differs essentially from that of the endogenous, or inward-growing; for, while in the former it constitutes the true bark, which is separable from the wood, in the latter it is only a hardening of the outward portion of the stem. We shall hereafter see that this covering has offices to perform, especially in the leaves, quite similar to the functions of the human skin, which we have already described.

1 AD-HER'-ENT, united.

2 GERM, beginning; origin; first principle.
3 OM-NIS'-CIENCE, universal knowledge.
4 "IN MIN'-IA-TŪRE," on a very small scale.
5 MYR'-I-ADS, immense multitudes.
6 RIND, skin; bark, or outer coat.
7 MAZE, intricate winding.

8 "LUCID WEBS," the webs of life, well
known to Him who wove them.

9 PROC'-ESS, pronounced pros'-ess.
10 Tis'-SÛE (tish-shu), that which has the
appearance of being woven.

11 CON-TIN'-U-OUS, separate; uninterrupt-
ed.

LESSON IV.

THE ROOTS OF PLANTS.

1. In what manner does the plant grow, and by what means is it nourished, are questions to be answered at the very outset1 of our inquiries2 into the physiology of vegetation. We are therefore next brought to consider those compound3 organs of plants which perform, among other functions, that of nutrition.

2. It is necessary to vegetable growth that certain substances should be absorbed, in a liquid state, through the roots, and that this nutritive liquid, or sap, should circulate through the stem to the leaves, which latter are the respiratory

or breathing organs, performing functions similar to the lungs of animals. From the leaves the sap is returned to the stem, after having been acted upon by the atmosphere, in a condition suitable for the formation of the new growth of the plant.

3. When the proper conditions of heat, light, and moisture allow the germination5 of the seed, which may be considered as a plant whose vital powers are dormant, its outer shell or covering bursts, and, in whatever position the seed is planted, the stem goes upward, while the rootlet invariably turns downward, and spreads out its little fibres to suck up nourishment from the earth.

4. In some rare instances roots may become branches, and branches act as roots. A maple-tree may be inverted," the branches being buried in the ground and the roots extended in the air, without killing the tree. The stems of some plants send out fibres which take root in the earth; and frequently twigs stuck in moist earth will take root and become large trees. Nearly two thousand years ago the Mantuan bard thus discoursed on this mode of propagation:

5.

6.

"These ways of planting Nature did ordain

For trees, and shrubs, and all the sylvan train.
Others there are, by late experience found:
Some cut the shoots, and plant in furrowed ground:
Some cover rooted stalks in deeper mould;
Some cloven stakes, and (wondrous to behold!)
Their sharpened ends in earth securely place,

And the dry poles produce a living race.

"Some bow the vines; and, buried in the plain,

Their tops in distant arches rise again.

Others no root require: the lab'rer cuts

Young slips, and in the soil securely puts:

Even stumps of olives, bared of leaves, and dead,
Revive, and oft redeem their withered head."

It is probable that some allowance is to be made for the poet's privilege in Virgil's account of the dry poles; but it is not uncommon to see posts, set out for fences, growing as trees.