398 



CEdogoniales 



precisely similar morphological characters. How have the androzoogonidia of the 

 nannandrous species arisen ? It is not at all probable that they have arisen from the 

 antherozoids of the monoecious species by an increase in size of the antherozoid mother- 

 cells, because two antherozoids almost invariably arise in each cell of the antheridium by 

 the division of the protoplast, whereas the entire protoplast of the androzoogonidangium 

 forms a single androzoogonidium. Seeing that this is also the case in the formation of 

 both the androzoogonidia and gynozoogonidia of the macrandrous species, and in the 

 gynozoogonidia of the nannandrous species, it is reasonable to suppose that the small 

 androzoogonidium of the latter has arisen merely by a reduction in size, which has gone 

 on hand in hand with a greater sexual differentiation. The specialization has become such 

 that the androzoogonidia are attracted to the vicinity of the oogonia and only germinate 



Fig. 253. (Edocladium protonema Stahl. A, vegetative plant showing the colourless rhizoids 

 and two of the resting 'cysts,' x 41. B, development of a male branch, x 330. C, a branch 

 with an oogonium, x 230. D, longitudinal median section through the zygote, x 230. 

 (After Stahl, from Wille.) 



either on their walls or on the walls of the supporting cells. The male plant which is then 

 developed is so reduced that there is at most only one vegetative cell, or sometimes none, 

 and one antheridium consisting of from one to five cells. The reduction of the male 

 filaments to ' nannandria ' is to be correlated with the fact that the antherozoids are set 

 free in the immediate vicinity of the oogonia, and, therefore, fewer of them are required in 

 order to ensure fertilization. Moreover, vegetative cells are unnecessary except as a 

 support for the single antheridium, for which one cell easily suffices (G. S. W., '12). 



Hirn ('00) is also in agreement with the view just expressed as to the origin of the 

 dwarf males of the nannandrous species of (Edogonium by the reduction and greater 

 specialization of the androzoogonidia of the macrandrous forms, but Pascher ('06) states 

 that the nannandrous forms have not arisen from the macrandrous forms. 



