DISPERSAL BY WIND. 



849 



Steppes of the East produce smooth, ellipsoidal i'ruits about the size of a hazel-nut 

 and so light that if one of them is laid on a person's open hand when his eyes are 

 shut he does not perceive its pi'esence. The extraordinarily small weight of these 

 fruits is due to the fact that their structure includes a layer resembling the pith of 

 tlie Elder. A fruit of Cachrys alpina measures 13 mm. in length and 10 mm. in 

 tliickness and weighs 007 grm.; another Cachrys fruit from Shiraz is 15 mm. long 

 and 10 mm. thick and weighs only 006 grm. When fruits of this kind fall they 

 are rolled along over the Steppe by the wind and only come to rest when they are 

 caught in some crack in the parched clay soil or get lodged in a hole in a rock. A 

 few Papilionacese also produce rolling fruits of the kind. One of the groups of 

 species belonging to the Medick genus, of which Medicago sciitellata (see üg. 464*) 

 may be taken as a type, has pods which are spirally curled into round balls and 

 which, when their seeds are ripe, detach themselves from their stalks and are rolled 



Fij^. 465. — Dispersion of fruits and seeds by the wlud. Plantago Cietica. 



a little way along the ground every time there comes a gust of wind. The same 

 thing happens in the case of Blumenbachia Hieronyrni, a native of South America, 

 belonging to the family Loasacete. Although the spherical fruit of this plant has 

 a diameter of 2b cm. it only weighs 034 grm. when thoroughly dried. As soon as 

 the seeds are ripe the fruit-stalk withers and the i-ound fruits, which are then left 

 lying loose upon the ground, are rolled away by the gentlest breeze. If their career 

 is stopped anywhere, and they get wetted by rain, the openings which are already 

 formed in them become enlarged and a quantity of wrinkled seeds fall out. 

 Paronychia, Kapella (see fig. 468 ^), a plant of wide distribution in the floral area of 

 the Black Sea, where it grows on dry rocky soil, brings small fruits to maturity in 

 the height of .summer, each of which is surrounded by silvery white membranous 

 bracts. When the season for the dispersion of these fruits arrives the entire tuft of 

 fruits, which is in the form of a spherical glomerule, becomes detached from the 

 branch on which it grows and lies lightly on the ground, where the least pufi" of 

 wind imparts to it a swift rolling motion. Sometimes if the ground is uneven the 

 rolling is converted into a hopping and springing motion, and occasionally such 

 masses of fruit are raised by powerful gusts of wind and carried considerable 

 distances through the air. In several species of Clover, such as Trifolium globosum, 

 T. suhterraneum, and T. vidificim (see fig. 468 '") there are only a few perfectly 



Vol. n. 104 



