210 



Introduction to Botany. 



the rich deposits which have accumulated at the mouths 

 of rivers. Much of the variation resulting in the great 

 multiplicity of form and structure which we now see has 

 originated in the different environments found by plants 

 by means of their migrant seeds. 



We see, then, that from many points of view it is im- 

 portant to plants to produce reproductive bodies capable 



of dispersion by their own 

 movements or by natural 

 agents outside of them- 

 selves, such as the wind, 

 running water, birds, in- 

 sects, etc. ; and we may 

 expect to find a great vari- 

 ety of devices intended to 

 facilitate the scattering of 

 fruits and seeds. 



145. Dispersion by Elas- 

 tic Tissues. The seeds 

 of the wild cranesbill are 

 scattered by a sudden springing outward of the valves of 

 the carpels. This action is caused by the outer layers of 

 cells being more succulent and shrinking more on drying 

 than the inner layers. The ripened seeds lie loosely in 

 the inflated lower portion of the carpels, and are conse- 

 quently thrown out when the carpels spring upward (see 

 Fig. 125). 



When the fruits of the common Euphorbias are picked 

 and placed on a table in a dry room, the carpels suddenly 

 spring apart as they become dry, and hurl the seeds with 

 considerable force to various parts of the room. Of course 

 they act in the same way under natural conditions out of 

 doors. 



FIG. 125. 



Elastic carpels of Cranesbill ; seed being 

 thrown on the right. After KERNER. 



