SEED DISTRIBUTION 325 



injury by the pounding of the surf. The abundant 

 springing up of many kinds of weeds (great ragweed, 

 etc.), on flooded lands after the water has subsided 

 is due to water-borne seeds. Many of the seeds so 

 transported are the small rounded seeds that are washed 

 along in the mud (not floating). Structures that enable 

 the wind to transport seeds are almost innumerable. 

 Chief among them are the long hairs on seeds and fruits 

 (thistle, milkweed, cottonwood); flattened extensions 

 into wings, which may be more or less spirally warped 

 (elm, maple, ash, catalpa) ; the inflorescence (tickle grass, 

 sycamore), or the whole plant (Russian thistle, and other 

 " tumbleweeds"), both rolled over the ground in the wind, 

 dropping the seeds as they go. 



593. Distribution by animals is accomplished in many 

 ways. Some seeds and fruits are provided with hooks or 

 prickles which become caught in the hairs of the passing 



FIG. 205. Spanish needles, cherry, acorn. Fia. 206. Touch-me-not. 



animal and so provide for the carrying of the seed (e.g. 

 cocklebur, sand-bur, stickseed, Spanish needles, bed- 

 straw, burdock, etc.). Other seeds are edible and so are 

 sought by various animals which eat many but drop some 

 in transporting them, or bury them for future consump- 

 tion, thus planting them (e.g. acorns, achenes of sun- 

 flowers, nuts, etc.). Probably the development of fleshy 

 fruits, however, is the one that most perfectly provides 

 for seed distribution. Animals of all kinds gather and 

 eat the fruits, and in doing so drop the sclerenchyma- 

 enclosed seeds (plums, cherries, etc.), or eat the fruits 



