440 



HOW PLANTS ARE SCATTERED 



appendaged. Winged fruits and seeds are borne on trees or 

 shrubs, and the wing is usually so adjusted as to make its 

 descent slow, with a spinning motion. As a rule, winged fruits 

 and seeds are much heavier than those with a tuft of hairs. 

 The fruits of the dandelion, the thistle, the fleabane, the arnica 

 (Fig. 166, III), and many other plants of the group Composite, 

 to which these belong, and the seeds of the willow, the milk- 

 weed, the willow-herb, and other 

 plants, bear a tuft of hairs. All 

 these seeds and fruits may in 

 windy weather be seen traveling 

 often to great distances. 



416. Tumble weeds. Late in 

 the autumn, fences, particularly 

 on prairie farms that are not 

 carefully tilled, or in pastures, 

 often serve as lodging places 

 for immense numbers of certain 

 dried-up plants known as tum- 

 bleweeds. These blow about 

 over the level surface until the 

 first snow falls and even after 

 that (Fig. 341), often traveling 

 for many miles before they come 

 to a stop, and rattling out seeds 

 as they go. Some of the com- 

 monest tumbleweeds are the 

 Russian thistle (Salsola Kali 

 var. Trayus, Fig. 340), the pigweed (Amarantus albus, Fig. 

 341), the tickle grass (Fig. 342), and a familiar peppergrass 

 (Lepidium). In order to make a successful tumbleweed, a 

 plant must be pretty nearly globular in form when fully grown 

 and dried, must be tough and lii> - ht, must break off near the 



O O 7 



ground, and drop its seeds only a few at a time as it travels. 

 A single plant of Russian thistle is sometimes as much as 



FIG. 340. Russian thistle 

 After Dewey 



