44 'J^HE VEGETATIVE FUNCTIONS OF PLANTS 



mesophyll cells of leaves first secretes a solution to the 

 outer surface of the cells, and that this solution becomes 

 concentrated by evaporation of the liquid solvent into 

 the intercellular spaces. The concentrated solution, then, 

 by osmotic action, causes more water to be withdrawn 

 from the interior of the cells, and these, in turn, are 



Fig. 34. — Petal of crown imperial {Frilillaria imperialis), showing the 

 remarkably large drop of nectar (n), secreted by the nectar gland near the 

 base of the petal. 



replenished from the fibro-vascular bundles. On account 

 of the tensile strength of the water column in these bundles 

 the water is raised as rapidly as it is transpired from the 

 leaves. 



Thus, while the physical processes of osmosis and 

 transpiration may be factors in causing the ascent of 



