MULTIPLICATION IN PLANTS 



467 



from these fragments. In multiplying certain cultivated plants 

 that do bear seeds it is sometimes found more practicable to use 

 this vegetative propagation than to depend upon seeds. This is 

 usually the case in 'layering "raspberries— bringing a stem over 

 until it touches the ground and then keeping it in this position 

 until it establishes a hold by means of adventitious roots (p. 1 1 7 ) . 



Fig. 190. Pollarded trees 



White poplars (Populus alba) pollarded to supply building poles in Chinese Tur- 

 kestan. Pollarding is the pruning, or trimming, of the branches of a tree so as to 

 make more twigs develop. (From a photograph by F. X. ^leyer, of the United States 



Bureau of Plant Industry) 



]Many plants bear upon their stems more buds than normally 

 develop into twigs or branches. When the stem is injured or 

 cut, some of these resting buds may begin to grow. We take 

 advantage of this fact when we wish to get many small twigs 

 rather than a few large branches (see Fig. 190). 



342. Grafting. Through continued cell division it is possible 

 for two surfaces of living cells to grow together even where the 



