VEGETATIVE REPRODUCTION 211 



portions grow up into plants like those from 

 which they have themselves been derived. 

 From simple beginnings the propagative 

 bodies advance in complexity, and other 

 structures, not in the first instance differenti- 

 ated as propagative bodies (e. g. thickened 

 stems in which food is stored), easily assume 

 this function of vegetative reproduction. 

 One may often trace the stages by which 

 this is brought about within the limits of a 

 group of closely related species. The Jerusa- 

 lem Artichoke, a sort of sunflower, is connected 

 by all imaginable transitions with other 

 species in which the underground stems have 

 not yet proceeded to form tubers (as in the 

 artichoke), but exist as mere whip-like runners 

 which turn up and only grow to new plants 

 by the slow and accidental process of rotting 

 off their connection with the parent plant. 

 In others the propagative character is still 

 less evident, and the storage function is 

 absent altogether. Finally, there are many 

 sunflowers which normally fail to produce 

 any underground runners at all. 



Thus, in spite of the endless variety in the 

 carrying out of the process, the essential 

 character of vegetative propagation is really 

 a simple one. In this respect it stands in 

 marked contrast to the other, the sexual, 

 reproductive process, which will form the 

 subject of the next chapter. 



