VEGETABLE NUTRITION.
Young plants first feed upon the store of nourishment placed in the seed, either in cotyledons,[3] or around them. Soon the little roots acquire the power to take their nourishment from the earth in which they are imbedded. They absorb moisture and the materials in solution, which rise through the latest formed wood as ascending sap, and in the cells of the growing parts, especially the leaves, undergo the transformations which convert inorganic into organic substances. Hales[4] calculated that the force which impels the sap in a grapevine in summer time is five times as great as that which drives the blood through the arteries of a horse.
SECTION OF AN ENDOGENOUS STEM.
Much of the water is evaporated. A large sunflower was found to exhale twenty or thirty ounces during the day, but very little at night. After the sap has been elaborated in the cells, under the influence of air and light, it descends just under the bark, in the cambium layer, and furnishes the material for the growth of cells and young buds, and nourishes all growing parts of the plant. This process takes place essentially in the earlier part of the season. In late summer and autumn the circulation in the leaves is impeded by the deposition of mineral matter, so that the plant or tree becomes gorged with the fluids which are ready to flow again at the coming of spring. It is this supply which is drawn upon in the “sugar bush.” A bucketful is often obtained from a single maple tree in twenty-four hours.
The cambium layer, or mucilaginous material between the bark and wood, hardens into cellular tissue and forms an annular growth. This is the case in all exogenous plants. If a section be made of one of them its age may be easily determined by counting the rings. The other great class of plants called endogenous, has the growing masses distributed through the stem. The common cornstalk is an illustration. Few things are more surprising than the way in which different plants manufacture from the same elements their
VARIOUS PRODUCTS.
This is noticeable in grafting. I have seen a thorn bush having one limb loaded with Bartlett pears. Now the material which ascended the stem was distributed to all the branches, but the cells in some of them manufactured it into thorn apples, while in this branch it was transformed into delicious fruit.
SHOWING A CYCAS, A YUCCA, TWO COCOANUT PALM TREES, AN INDIAN CORN STEM, AND A BANANA.