20 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 



Fig. i6. — ^Leaf of a banana {Miisa sapientum), 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 

 54 sq. ft. of green tissue to the light. (Photo by the author.) 



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. 



