DEVELOPMENT OF PLANTS 349 



has here gone a step further. They are so constituted that they 

 now appropriate all the food in their respective sporangia. 



(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 the other orders. This 

 growth is somewhat different from previous cases in that at first 

 there is no outgrowth of the spore but simply the formation of a 

 varying number of nuclei within the spore. Later these nuclei 

 develop cell walls and subsequent growth ruptures the spore. 

 In this way the microspore forms two cells while in the sporangia, 

 a small one often compared to a remnant of the male gameto- 

 phyte or prothallium and a large cell which ultimately forms a 

 single antheridium. At about this stage of germination the 

 microsporangium opens by a vertical cleft, permitting the scatter- 

 ing of the spores. The larger cell of the microspores now forms 

 a central mass of gamete mother cells which are surrounded by a 

 single layer of wall cells (Fig. 243, i). The male gametes are of 

 the same character as noted in Lycopodium and are set free 

 by the disintegration of the wall cells. The megaspores begin to 

 germinate even before they have reached their full size. The 

 nucleus of a megaspore divides repeatedly, forming numerous 

 nuclei which become arranged about the walls of the young spore. 

 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 

 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 

 gametophyte. We see that the gametophyte is becoming para- 



