344 



Kansas Academy of Science. 



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0. v^— -^ 



iLxnt Ferti li^(ltio)v %Emhyyo\og^ 



grain germinating on the stigma. iV^ represents a stamen with its 

 filament, anthers and pollen. is an enlarged pollen grain or mi- 

 crospore. Among mosses when certain spores germinate there are 

 developed plants of considerable size with rhizoids, stems, leaves 

 and sperm-producing bodies, the antheridia; and other spores de- 

 velop into similar plants with egg-producing organs, the archegonia. 

 Such organisms are known to the botanists as the male and female 

 gametophy tes ; and among mosses they are the chief food-elaborating 

 structures. But among flowering plants, the cottonwood, for ex- 

 ample, the sperm- and egg-producing gametophytes have degener- 

 ated till only a few cells remain, and the organisms are entirely 

 dependent on food stored in the spore by the parent sporophyte. 

 The germinating microspore of the cottonwood shows only two or 

 three gametophyte cells, viz., a tube-producing nucleus, (9-2, and a 

 mother sperm-cell, 0-1. 



It will be remembered that when the animal mother germ-cells 

 mature (see diagrams F and H), one functional q^^ nucleus is 

 produced and four functional sperms; but the botanist has found 

 that in plants these germ-cells are all spores. Among mosses and 

 common ferns all the spores are equal in size and each may de- 

 velop, so far as the botanist knows, into a male or a female gam- 

 etophyte; or in some species the spore develops into a gametophyte 

 which bears both kinds of sexual organs, the antheridia and arche- 

 gonia, containing at maturity respectively the sperms and eggs. 

 In marsilia, selaginella, the gymncsperms and the angiosperms, the 

 spores produced by the maturing mother germ-cells are of unequal 

 sizes, and are therefore named microspores and megaspores. The 



