MORPHOLOGY OF REPRODUCTIVE ORGANS 221 



Fig. 481. 



antheridium consisting of an incomplete wall and two internal 

 cells, each of which gives rise to two antherozoids or male 

 gametes ; in the Phanerogams even this differentiation dis- 

 appears. In Marsilea and Selaginella, the microspore gives 

 rise to a small, somewhat oval multicellular body which pro- 

 duces antherozoids in its internal cells. 



The fenaale gametophyte also shows a gradual degeneration. 

 In Salvinia the megaspore bursts at its apex (fig. 481), and the 

 prothallium is developed as a 

 curiously shaped green body, 

 the greater part of which 

 remains within the spore. 

 The free part bears the 

 archegonia. In Selaginella 

 and Isoetes the development 

 is still more markedly en- 

 dosporous. The prothaUiuiu 

 is developed inside the mega- 

 spore (fig. 482), which does 

 not open till the former is well 

 advanced ; in some oases, 

 indeed, until the archegonia 

 are rnature and the oospheres, 

 or female gametes which they 

 contain, are ready for ferti- 

 lisation. In the Phanerogams 

 the megaspore is never ex- 

 posed, and the prothallium 

 or gametophyte is therefore 

 always completely internal. 

 In verj' rare cases it partly 

 projects from the apex of the 

 megaspore, but this is very 

 exceptional. In the Gym- 

 nosperms {fig. 483) it still 

 consists of a large number of 



cells ; while its morphological nature was not understood, it 

 received the name endosperm, which still continues to be applied 

 to it. In the Angiosperms the reduction is still ixiore complete. 

 "When the gametophyte is mature, it consists of only a few cells or 

 masses of protoplasm, some of which have no cell- wall {fig. 484). 

 In the Gymnosperms the archegonia, usually several in number, 

 are well developed, and are much like those of Selaginella. 



Fi'/. 481. Gametophyte produced by the 

 megaspore of Salvinia. pro. Prothallium 

 bearing r(, youug sporophyte. Alter 

 Pringsheim. 



