CHAPTER VHr 



THE WAYS IN WHICH SUBSTANCES ARE TRANSPORTED 

 THROUGH PLANTS AND FINALLY REMOVED THERE- 

 FROM. 



Transfer, Transpiration, Excretion 



HE living plant, as the reader of the foregoing pages 

 will surely agree, can be viewed as a kind of central 

 station for the transformation of substance and energy, 

 both of which forever are streaming into, passing 

 through, and issuing forth from the plant, undergoing en route 

 quite definite changes in correlation with adaptive results. These 

 transformations we have already considered in our chapters upon 

 Photosynthesis, Respiration, and Metabolism, while their Absorp- 

 tion was the theme of the chapter just finished; but we still have to 

 consider their passage through the plant and their final removal 

 therefrom. These matters can be treated conveniently together 

 as they are in this chapter, although, for a practical reason which 

 will later appear, we may best reverse the natural order, and 

 treat first the subject that logically should be last. 



The most abundant of the substances transferred and elimi- 

 nated as well as absorbed, by plants, is water. Most people are 

 aware in a general way that plants are forever giving off water 

 as vapor to the air, although they have little idea of its amount. 

 The fact can be demonstrated, by the way, very conclusively to 

 the eye by placing a potted plant, of which pot and soil have 

 first been enwrapped by a water-tight covering, in a glass case 

 or bell-jar, after which, within a few minutes, there will collect 



on the glass a cloud of water-drops which can have come from 



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