DISPERSION OF SEED. 141 



the rest, and filling the whole cavity of the pericarp. When, 

 however, the embryo is fully developed within it, the ovule 

 becomes the seed, and the ovary the fruit. The seed is 

 detached from the parent plant, and the life which has passed 

 away from the other parts in succession, now lies dormant 

 within its folds. 



The separation of the seed at maturity from the parent 

 plant may be regarded as the parturition of the plant. 

 Sometimes the pericarp or seed-vessel opens with a spring- 

 like mechanism, and the seeds are thrown to some con- 

 siderable distance. The pericarp of the common garden 

 balsam, (Impatiens,) and that of the castor oil plant, (Ri- 

 cinus,) may be given as illustrations. When the pericarp 

 or seed-vessel does not open elastically, and the seeds re- 

 main attached to its walls, the atmosphere sometimes frees 

 them from their confinement. We see every day the wind 

 transporting the seeds of plants which have developed little 

 feathery appendages, contrivances evidently intended to 

 catch the breeze, by means of which they are detached from 

 the pericarp and carried often to a great distance from the 

 parent plant. Neither is there any mistaking the intention 

 of nature in furnishing the seeds of some plants with barbs 

 or hooks, by means of which they adhere to the dress of the 

 passing traveller, who thus unconsciously becomes the in- 

 strument in effecting their removal. In the autumnal 

 months, all persons must be familiar with seeds which, thus 

 furnished, have attached themselves to their dress, and 

 forced themselves on their attention. The seeds of the 

 Spanish Needles, (Bidens bipinnata,) are in this respect, 

 particularly troublesome. 



If the seed, thus separated by any of these agencies, is 

 favorably located, all is quiet until the return of suitable 

 conditions of temperature, air, and moisture, when the vital 



