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 bell- jar containing water; 4, iron support. In 
this experiment the eosin rose rapidly in the branch. (Modified from 
H. H. Dixon.) 
the nbro-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 nbro-vascular bundles, and 
yet the eosin will rise in the branch and into the leaves. 
