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. 
