HOW PLANTS ARE SCATTERED 



379 



even after that (Fig. 269), often traveling for many miles 

 before they come to a stop, and rattling out seeds as they 

 go. Some of the commonest tumbleweeds are the Russian ' 

 thistle (Fig. 268), the pigweed (Amarantus albus, Fig. 269), 

 the tickle-grass (Fig. 270), and a familiar pepper-grass 

 {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 light, must break off 

 near the ground, and drop its seeds only a few at a time 

 as it travels. A single plant 

 of Russian thistle is some- 

 times as much as three feet 

 high and six feet in diameter 

 and carries not less than two 

 hundred thousand seeds. 



449. Many -Seeded Pods 

 with Small Openings. — 

 There are many fruits which 

 act somewhat like pepper- 

 boxes. The capsule of the 

 poppy is a good instance of 

 this bind, and the fruit of 

 lily, monkshood (Fig. 168), 

 columbine, larkspur, and 

 jimson weed (Fig. 271) acts 

 in much the same way. 

 Clamping the dry peduncle 

 of any one of these ripe 

 fruits, so as to hold it up- 

 right above the table-top, and then swinging it back' and 

 forth, will readily show its efficiency in seed dispersal. 



Fio. 268. — Eussian Thistle. 



