26 
THE VEGETATIVE FUNCTIONS OF PLANTS 
plants is called transpiration, in recognition of the fact 
that the moisture must pass through the epidermis. 
31. Function and Structure. As stated in Chapter I, 
the function of an organ cannot be intelligently discussed 
unless its structure is understood, and vice versa, the 
structure of any part is without meaning, except as 
PIG. 16. Leaf of a banana (Musa sapienlum), showing enormous 
development of the blade, and also how easily a leaf-blade may be torn 
in the absence of a marginal vein. This leaf-blade (i.e. without the 
petiole) measured over 15 ft. long and 3 ft. wide, thus exposing over 
45 sq. ft. of green tissue to the light. 
viewed in the light of its function. Therefore, if we wish 
to understand transpiration and the other functions of 
leaves, we must first ascertain their structure. This has 
significance for us only in the light of their physiological 
work. 
