ECOLOGY OF FRUITS 193 
238. Tumbleweeds. — Late in the autumn, fences, par- 
ticularly on prairie farms that are not carefully tilled, 
often serve as lodging-places for 
immense numbers of certain dried- 
up plants known as tumbleweeds. 
These blow about over the level 
surface until the first snow falls 
Fic. 144. Russian Thistle. 
and even after that, often 
traveling for many miles be- 
fore they come to a stop, and 
rattling out seeds as they 
go. Some of the commonest 
tumbleweeds are the Russian 
thistle (Fig. 144), the pig- 
weed (Amarantus albus), the tickle-grass (Fig. 145), and 
a familiar pepper-grass (Lepidium). In order to make a 
Fic. 145. Panicle of Tickle-Grass, 
a Common Tumbleweed. 
