DEVELOPMENT OF PLANTS 



317 



not develop and are ultimately consumed in nourishing the mega- 

 spores. As a result of the large amount of food transferred to 

 the megasporangium, both it and especially the two or four 

 spores become much larger than the others (Fig. 242, 3-6). 



(b) The Germination of the Spores. — The most important and 

 suggestive feature in the life history of Selaginella appears in 

 the germination of the spores. The spores germinate in the 

 sporangia and not after being shed, as in other ferns. The 

 microspore forms two cells while in the sporangia, a small one 



Fig. 243. Gametophyte and young sporophyte of Selaginella: 7, section 

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

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

 previous groups of ferns ; an, antheridium consisting of a layer of wall 

 cells which enclose the gamete mother cells. 7A, a male gamete. 8, sec- 

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

 attained in the sporangium. 9, mature female gametophyte that has rup- 

 tured 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, f, and the suspensor, s. 10, young sporophyte 

 with root, stem and leaves emerging from the gametophyte. 



often compared to a remnant of the male gametophyte or pro- 

 thallium and a large cell which ultimately forms a single anthe- 

 ridium. At about this stage of germination the microsporan- 

 gium opens by a vertical cleft, permitting the scattering of the 



