RIPENING AND DIFFUSION OF SEEDS. 129 



lapsing with the sun's heat, press with their hard edges 

 upon the slope of the smoothly polished seed, and along 

 this the edge slides forcibly down, and the seed is con- 

 sequently torn from its fastening, and thrown with a 

 jerk to a considerable distance. It is worthy of remark, 

 also, that before the seed is ripe, the whole head hangs 

 drooping with the persistent flower cup spread over it, 

 like an umbrella, to guard it from rain and dews that 

 would retard its ripening; but as soon as it is ripe, it 

 rises to an upright position with the cup for a support, 

 while it gains in this way a greater elevation for scat- 

 tering the seeds. In a drawer, I found the ripe heads 

 of heart's ease project their seeds about two feet ; and 

 when enclosed in a pill box, they may be heard suc- 

 cessively popping against the lid as they are discharged. 

 The above is an instance of a seed-vessel bursting 

 from becoming dry. De Candolle gives a still more 

 singular one in the rose of Jericho from its meeting 

 with moisture. "This little plant," he says, "grows 

 in the most parched deserts. By the time it dies, 

 owing to the great drought its tissue has become almost 

 woody, its branches fold over each other, till the whole 

 assumes the form of a bah 1 ; its seed vessels have their 

 valves tightly shut, and the plant remains adhering to 

 the ground by a solitary branchless root. The wind, 

 which always acts powerfully along the surface of a 

 sandy plain, uproots the dry ball and roUs it along. If 

 it now chance to meet with a plash of water whilst 

 performing its constrained but necessary journey, it 

 speedily imbibes the moisture, which causes the 

 branches to unfold and the pericarps to burst; and 



