26 



PRACTICAL COURSE IN BOTANY 



anchorage and left to drift about on the ground. The spread- 

 ing, bushy tops become very light after fruiting, so as to be 

 easily blown about by the wind, dropping their seeds as they 

 go, until they finally get stranded in ditches and fence corners, 

 where they often accumulate in great numbers during the 

 autumn and winter. 



24. The advantages of dispersal. — Seed cannot germinate 

 unless they are placed in a suitable location as to soil, moisture, 

 and temperature. In order to increase the chances of secur- 

 ing these conditions, it is clearly to the advantage of a species 

 that its seeds should be dispersed as widely as possible, both 

 that the seedlings may have plenty of room, and that they 

 may not have to draw their nourishment from soil already 

 exhausted by their parents. The farmer recognizes this 



principle in the rotation of 

 crops, because he knows that 

 successive growths of the 

 same plant will soon exhaust 

 the soil of the substances i*e- 

 quired for its nutrition, while 

 they may leave it richer in 

 nourishment for a different 

 crop. 



25. Self-planting seeds. — 

 Dispersal is not the only 

 problem the seed has to meet. 

 The majority of seeds cannot 

 germinate well on top of the 

 ground, and must depend on 

 various agencies for getting 

 under the soil. Some of them 

 do this for themselves. The 

 seeds of the stork's-bill, popularly known as ''filarees," have 

 a sharp-pointed base and an auger-shaped appendage at the 

 apex, ending in a projecting arm (the '' clock" of the filaree) 

 by which it is blown about by the wind with a whirling motion 



Fig. 45. — Self-planting pod of peanut. 



