LOSS OF WATER 



45 



sap, the physiological process of secretion is also of very- 

 great importance. Moreover, on this basis we are able 

 to account for the ascent of sap in submerged aquatic 

 plants, like eel-grass, pond-weed, and others, where tran- 

 spiration is not possible. In fact it may be shown, 

 experimentally, that a leafy branch can raise water through 



Fig. 35- — Experiment to show that secretory action in the cells of a 

 leaf are able to cause the rise of liquid in a branch, when evaporation from 

 the leaf-surfaces is impossible, i, Beaker containing solution of eosin; 

 2, cork; 3, inverted glass beU-jar containing water; 4, iron support. In 

 this experiment the eosin rose rapidly in the branch. (Modified from 

 H. H. Dixon.) 



the fibro-vascular bundles, even when submerged. The 

 apparatus is set up as shown in Fig. 35, where the leafy 

 branch, immersed in water in an inverted glass bell-jar, 

 has the cut end of the stem in a solution of eosin or red 

 ink. Under these conditions only secretion can operate 

 to withdraw water from the fibro-vascular bundles, and 

 yet the eosin will rise in the branch and into the leaves. 



