Forms and growth of seed 



lOI 



grass, etc. Such plants generally grow in light soils and 

 either have very light root sys- 

 tems, or are easily broken from 



Panicle of " old witch 

 a common tumble 



231. — A fruiting plant of winged pigweed 

 (Cycloloma), showing the bunchy top and weak 

 anchorage of a typical tumble weed. 



their anchorage and left to drift 

 about on the ground. The 

 spreading, 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. 



In the Japan varnish tree {Sterculia platanifolid) the 

 seeds remain attached all through the winter to the open 

 follicle, which becomes very light when dry, and acts as a 

 sort of float for wafting the seeds away on every breeze. 



135. Explosive Capsules. — Some plants undertake to 

 disperse their seeds without the intervention of any external 



© 



233 234 2j3 



233-235. — 233, A pod of wild vetch, with mature valves twisting spirally to 

 discharge the seed; 234, pod of crane's-bill discharging its seed; 235, capsules of 

 witch-hazel exploding. 



