. Botany all the year round; a practical text-book for schools. Botany. 164 THE STEM PROPER. 308. — Diagram showing gen- eral movement of sap. perish. Figure 308 will give a good general idea of the movement of sap in trees, the !» / arrows indicating the direction of the movement of the different substances. 233. Sap Movement not Circula- tion.— It must not be supposed that this flow of sap in plants is analogous to the circulation of the blood in animals, though frequently spoken of in popular language as the " circulation of the ; There is no central organ like the heart to re
. Botany all the year round; a practical text-book for schools. Botany. 164 THE STEM PROPER. 308. — Diagram showing gen- eral movement of sap. perish. Figure 308 will give a good general idea of the movement of sap in trees, the !» / arrows indicating the direction of the movement of the different substances. 233. Sap Movement not Circula- tion.— It must not be supposed that this flow of sap in plants is analogous to the circulation of the blood in animals, though frequently spoken of in popular language as the " circulation of the ; There is no central organ like the heart to regulate its flow, and the water taken up by the roots does not make a continual circuit of the plant body as the blood does of ours, but is dispersed by a pro- cess of general diffusion, part into the air through tran- spiration, and part through the plant body as food, wherever it is needed. 234. Unexplained Phenomena. — While root pressure will account for the rise of sap to a certain extent, none of the causes assigned by physiologists are sufficient to explain all the phenomena. The highest force as yet proved to be exerted by it is sufficient to balance a column of water only ten to fifteen meters (thirty to fifty feet) high. The power with which it acts seems to vary in different plants. In the nettle it is capable of lifting the sap to a height of about meters (15 feet) and in the grapevine more than II meters, or about feet. It is claimed that in the birch it exerts a lifting force nearly equal to the pressure of a column of water eighty-five feet high, but even this is quite inadequate to explain the rise of sap to the tops of trees three hundred and four hundred feet high, Hke the giant redwoods of California or the still taller blue gums of AustraUa. Capillary attraction and the buoyant force of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of thes
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