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PHENOMENA OP VEGETATION.

gitudinal fibres, which cross each other, and form a kind of net-work. The wood lies under the bark; it constitutes by far thegreatest part of the tree or vegetable. It consists of concentriclayers, which are composed of longitudinal fibres. The pitk issituated in the centre of the wood : it is a very spongy substance,and contains a vast number of celts. Through all these differentparts of die plant, vessels are abundantly distributed, by means ofwhich the functions necessary for the life and re-production ofthe vegetable are carried on. The conditions necessary for thatpurpose constitute the chemical phenomena of vegetation.

PHENOMENA OF VEGETATION.

If a seed, which consists of three principal parts, namely, thecotyledons, the radicle, and the plumula, is placed in a situationfavourable to i(s vegetation, it absorbs moisture, swells, and be-comes soft. The radicle is converted into a root, and penetratesinto the earth. The cotyledons emerge above the ground, andexpand in the form of leaves, (called the seminal leaves); andthe plumula becomes the stem, to which the leaves are affix-ed. The whole seed, during this time, changes to a substance ofa saccharine nature, which serves for the first food of die plant.When these appearances take place the seed is said to germinate orgrow. The food which was laid up in the seed for the embryoplant is then exhausted, and the plant derives its future nourish-ment principally from the air and soil.

FOOD OF PLANTS.

The food of plants consists of water impregnated with vegeta-ble and animal matter, and several gases ; but water and air formthe principal part of the food of every vegetable. They are decom-posed in the vessels of the plant. The hidrogen of the water isretained; the oxigen is also absorbed, but the greatest part of itappears to be evolved again by die leaves. Water also serves to