CHAPTER VII 



REPRODUCTION 



THE subject of reproduction has been more fully and more 

 exactly studied by morphologists than by physiologists. 

 It has been meditated upon more than it has been investi- 

 gated through experiment. Yet there are certain results of 

 comparatively recent work, and there are certain hypothe- 

 ses, which must be considered in any discussion of the 

 physiology of plants. 



In the vegetable as in the animal kingdom the span of 

 life of the individual organism is limited. In many cases it 

 is limited by perfectly obvious influences; in most it is 

 limited by means little understood even if apprehended at 

 all. In many plants and animals there are no evident rea- 

 sons inherent in the organisms themselves why they should 

 not continue to live indefinitely. Influences wholly external 

 and only slightly controllable by the organism determine 

 and terminate its career. The effects of these influences are 

 to be distinguished from the irritable responses which we 

 have studied in the preceding chapter. Irritable response 

 depends upon a degree of sensitiveness possessed only by the 

 living organism, although this sensitiveness is dependent 

 upon the sum of the physical and chemical conditions pre- 

 vailing in the organism (p. 186). But the influences which 

 terminate its career exceed the powers of resistance, reac- 

 tion, or response, of the organism. They act upon it as 

 upon any lifeless thing of similar composition and structure, 

 and they produce on the lifeless similar effects to those pro- 

 duced on the living body. For example, the heavy wind 

 which uproots a tree would bring it to the ground were it 

 alive or dead. Uprooted it would dry faster than if its 

 roots were still in the soil. It is after all the drying, follow- 

 ing the uprooting, and not the uprooting itself, which is the 



