74 



WORK OF THE STEM 



Having become somewhat acquainted with the structure of 

 the stem, he is now in a position to investigate the question how 

 the various fluids, commonly known as sap, travel about in it. 1 



It is important to notice 

 that sap is by no means 

 the same substance every- 

 where and at all times. 

 As it first makes its way 

 by osmotic action inward 

 through the root hairs of 

 the growing plant it differs 

 but little from ordinary 

 spring water or well water. 

 The liquid which flows 

 from the cut stem of a 

 "bleeding" tree or grape- 

 vine which has been 

 pruned just before the buds 

 have begun to burst in the 

 spring is mainly water, 

 often .with a little dissolved 

 organic acids, proteids, and 



sugar. The sap which is 

 obtained from maple trees 

 in late winter or early 



FIG. 73. Channels for the movement of 

 water, upward and downward 



The heavy black lines in roots, stems, and spring, and is boiled down 

 leaves show the course of the fibro-vascular f^^ cnVm-i Q-[ sugar is richer 



bundles through which the principal move- 

 ments of water take place. After Frank in nutritious material than 

 and Tschirch the water of the grapevine, 



while the elaborated sap which is sent so abundantly into the ear 

 of corn at its period of filling out, or into the growing pods of 

 beans and peas, or into the rapidly forming acorn or the chestnut, 

 contains great stores of food suited to sustain plant or animal life. 



1 See the paper on "The So-called Sap of Trees and its Movements," by 

 Professor Charles R. Barnes, Science, Vol. XXI, p. 635. 



