THE STRUGGLE FOE EXISTENCE. 



201 



then blown along for great distances, until it is brought to a 

 standstill by a fence or other obstacle. The Russian thistle, 

 of which a small branch is shown in Fig. 184, forms, when 

 growing luxuriantly, roundish bushy masses, as much as 

 three feet high and six feet in diameter. These when dead 



Fig. 183. — Partly matured Panicle of Tickle-Grass.* 



and dry, but loaded with seeds, drift before the wind in such 

 quantities that they often form sloping embankments reach- 

 ing to the tops of high fences. One such plant has been 

 estimated to carry with it as many as 200,000 seeds. 



1 Panicum capillare. 



