906 ECOLOGY 



r 



commonly completely pendent (anatropous) ; in the last case the close 

 application of the funiculus to the integument causes a suture, the 

 raphe (figs. 582-584). 1 The young sporophyte or embryo at first grows 

 vigorously, usually becoming differentiated at seed maturity into the 

 embryo root (radicle), the embryo stem (hypocotyl), one, two, or more 

 seed-leaves (cotyledons), and the embryo shoot (plumule)? The seed 

 also contains foods that are utilized by the young sporophyte during its 

 second phase of activity, commonly called germination? These foods 

 may accumulate within the cotyledons (as in peas and beans, fig. 1205), 

 which in that event occupy most of the space within the testa, or they 

 may accumulate in a tissue surrounding the cotyledons (as in most 

 monocotyls, fig. 1204), this tissue being called endosperm if arising 

 within the embryo sac, and perisperm if arising from the nucellus. 

 Most seeds mature in the season of anthesis. Some plants with autumnal 

 flowers, such as Hamamelis and Colchicum, mature seeds the folk wing 

 season, and in some plants with vernal flowers, such as the pines 

 and certain oaks, maturation comes in the second season. 



The rdle of seeds. Primarily seeds are disseminules, and ma ly of 

 their chief structural features are associated with dispersal. Of almost 

 equal importance in many plants, especially in annuals and bienni ils, is 

 their protective r61e, since in no other form is the seed plant so immune 

 to danger as in the seed. Though they are often so regarded, seeds are 

 in no sense reproductive organs. The reproduction of which the seed 

 is the result, takes place previously within the flower, while the seed rep- 

 resents in a state of arrested development the protected offspring of that 

 reproduction. Thus the unique feature of the seed plants is the sepa- 

 ration of reproduction from protection and dispersal; post-reproductive 

 disseminules, the seeds, take the place of reproductive disseminules, the 

 asexual spores. 



The protective structures and relations of seeds. The protection oj 

 developing seeds. Developing seeds are protected from transpiration 

 and from other dangers by the ovary wall, which thickens and hardens 

 into the fruit wall or pericarp. It has been thought that grazing ani- 

 mals might eat the young fruits, so that the sourness, bitterness, or hard- 

 ness of fruits that later become edible have been regarded as advantageous 

 in protecting them from such dangers. In some cases, as in the jimson 



1 Most of these terms apply also to seeds. 



* In the orchids and in some parasites the embryo remains undifferentiated. 



* Little or no food is found in minute seeds, as in those of the orchids. 



