DISPERSAL BY WIND. 



819 



offshoots exclusively. The detachment takes place in different ways in these 

 "Viviparous" Grasses. Usually the sprouts loosen from the erect panicles of the 



Fig. 452. — Polygonum vivipanmi. 



1 Entire plant ; one spike bears flowers only, the other carries tubers on the lower half and flowers above. 2 a whole plant 

 whose spike bears tubers only. On some of the tubers small foliage-leaves have already developed, s-b Fallen tubers in 

 successive stages of development ; nat. size. * A fallen tuber magnified, lo The same in longitudinal section. 



swaying haulm, and are scattered by the wind; but sometimes the separation does not 

 occur until the stem is bent down to the ground with the weight of the crowded 

 offshoots in the panicle. In this case the offshoots strike root where the panicle 



