334 



REPRODUCTION OF SELAGINELLA 



Subsequently walls are formed about the nuclei at the apex of 

 the spore (Fig. 243, 2) and by further division a mass of cells 

 results, in the outer part of which the first divisions of the arche- 

 gonia arise. At this stage of development, or earlier, the mega- 

 sporangium opens by a vertical cleft permitting the discharge of 

 the spores. It must be borne in mind that this origin of the 



Fig. 243. Gametophyte and young sporophyte of Selaginella: i, section 

 of a microspore that has nearly completed its germination — p, a single cell 

 that is possibly a remnant of the large gametophyte or prothallium of pre- 

 vious groups of ferns; an, antheridium consisting of a layer of wall cells 

 which enclose the gamete mother cells. lA, a male gamete. 2, section 

 of a megaspore, showing the stage of germination that is usually attained 

 in the sporangium. 3, mature female gametophyte that has ruptured the 

 wall of the megaspore, thus exposing the archegonia, ar, one of which has 

 developed a young sporophyte or embryo with root, r; stem bearing two 

 leaves, st, foot, /, and the suspendor, 5. 4, young sporophyte with root, 

 stem and leaves emerging from the gametophyte. 



gametophyte is of a radically different nature from any case pre- 

 viously noted. Heretofore the gametophyte always had an inde- 

 pendent existence and the sporophyte for varying periods of time 

 was a parasite upon it. In Selaginella you note the beginning 

 of a reversal of this relation, for the sporangia remain green 

 and continue to nourish the spores during their germination; in 

 other words, during the early stages in the development of the 



