160 Minnesota Plant Life. 



the spore-wall breaks, as it does eventually, the sperm-cells are 

 liberated and swim away in the water after some rain or heavy 

 dew. When the large-spores germinate each produces a fe- 

 male plant which, like the male, remains within the spore and 

 does not push out as did the sexual plants of liverworts, mosses 

 and the larger club-mosses. The female is very much larger 

 than the male, and each plant fills the spore from which it de- 

 veloped. When the female is mature, one, or sometimes more, 

 egg-producing organs are formed at the surface of the cell-mass 

 inclosed in the large-spore. After the egg-organ with its in- 

 closed egg has matured, the wall of the large-spore breaks just 

 over the imbedded neck of the egg-organ. This permits sper- 

 matozoids to enter and by means of one of them the egg is 

 fecundated and begins segmenting into an embryo in which 

 stem-areas, root-areas, leaf-areas and nursing-foot-areas are pro- 

 duced. In the smaller club-moss a great reduction of the sex- 

 ual generation is apparent. The sexual plants do not even 

 come outside of their spore-walls. They do no independent 

 vegetative work but the species depends for its subsistence upon 

 the starch-making power of the spore-producing plant. 



Origin of the seed of higher plants. The smaller club- 

 mosses while of slight economic importance are of extraordinary 

 scientific interest because they illustrate how in the history of 

 the vegetable kingdom that important structure, the seed of 

 higher plants, probably originated. The habit of the female of 

 remaining within the spore must have antedated the origin of 

 the seed. In seeds not only does the female remain within the 

 spore but the spore remains within its case and the female ob- 

 tains fecundation of her egg by the cooperation of a pollen-tube, 

 while the spore-case need not open. When the embryo has 

 begun to form from the egg the whole spore-case, with some 

 adjacent layers of cells, ripens and a seed is the result. The 

 smaller club-mosses foreshadow this still more strongly in some 

 species where the large-spores begin to germinate internally be- 

 fore they fall from their spore-cases. Yet no smaller club-moss- 

 plant ever really produces a seed, for in all of them sooner or 

 later the spore is ejected from its case and thus there is pre- 

 vented from arising the exact combination of conditions upon 

 which seed formation depends. 



