PTEBIDOPHYTA— LYCOPODIN.E 



163 



small amount of protoplasm surrounding a large central vacuole. 

 By free cell-formation a small primary prothallium is formed at 

 the apex of the spore, which is soon separated from the remainder 

 of the spore-cavity by thickening of the cell-walls of its lower 

 layer, forming a diaphragm not unlike that of Salvinia. The 

 protoplasm of the lower part of the spore increases till the cavity 

 is filled with it. By free cell formation it develops a tissue 

 much like that of the primary prothallium but with larger cells. 

 This has been called the endosperm. The upper portion of the 

 prothallium is after its formation exposed to light and air by the 



Fig. 920. 



arch. 



Fig. 920. Germiuation of macrospore of Selaginella. After Pfetfer. arch. 

 Archegonium. em, em'. Young embryos. 



rupture of the macrospore at its apex ; it then becomes green 

 from the development of chloroplastids. Generally it bears only 

 one archegonium, always only a limited number. Frequently 

 the number produced depends upon whether the first becomes 

 fertihsed. They have the same structm-e as those of the euspo- 

 rangiate ferns. 



The archegonia have the usual structure found in the group. 

 Fertilisation of its oosphere is also normal. 



'When the zygote is formed and its germination begins, the 

 process is similar to that of Lycopodium. The hypobasal seg- 

 ment becomes the suspensor, which by its elongation forces the 



M 2 



