. Annual report of the Agricultural Experiment Station. Cornell University. Agricultural Experiment Station; Agriculture -- New York (State). 482 Agricultural Experiment Station, Ithaca, N. Y. Just why so much water is required b^^ the growing plant and how it obtains this supply is not usually understood. It has been the subject of considerable re- search and even now presents inter- esting problems for further study. The roots of the plant are its feeders and all of the water ordinarily used by it passes in through these chan- nels. The particles of soil hold a film of w^ater in firm contact
. Annual report of the Agricultural Experiment Station. Cornell University. Agricultural Experiment Station; Agriculture -- New York (State). 482 Agricultural Experiment Station, Ithaca, N. Y. Just why so much water is required b^^ the growing plant and how it obtains this supply is not usually understood. It has been the subject of considerable re- search and even now presents inter- esting problems for further study. The roots of the plant are its feeders and all of the water ordinarily used by it passes in through these chan- nels. The particles of soil hold a film of w^ater in firm contact. The roots and rootlets of the plant, in burrowing through the soil, come into intimate relation with these soil particles (Fig. 140). The finer the soil, the closer the relation estab lished between it and the roots. The The roots are thus surrounded by a thin film of water, a portion of which they are able to absorb. The water passes up through the tissues of the plant, carrying with it soluble plant food which is conveyed to the manufacturing or elaborating or- gans, the leaves. There, in the pres- ence of sunlight, the fixation of carbon from the air takes place and by means of the movement of the sap the now organized material is carried to all growing parts of the structure. That part of the water no longer required passes off through the breathing pores of the leaf, called stomata. As evaporation is a cooling process, there is no doubt that this loss of water has an important influence in lowering the temperature of foliage and in promoting the fixation of carbon. As alread}' stated, the plant roots can absorb food only in the soluble form, and the passage of a large quantity of water through their tissues is necessary to furnish the supply of min- eral elements required by growth. Not only is a large quantity of moisture demanded for the direct use of the plant, but its presence in the soil is necessary in order that the plant food may. 140.—A corn plant showing the
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