44 THE 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by osmotic action, causes more water to be withdrawn 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 imperialist, showing the 
remarkably large drop of nectar (n), secreted by the nectar gland near the 
base of the petal. 
replenished from the nbro-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 
