i 7 8 



PYREXOMYCETES 



[CH. 



There is an obvious suggestion in these phenomena of a transition 

 between the monoecious and dioecious condition but it is not clear in which 



direction the series should be read. It might be 

 inferred that the male plant had become atro- 

 phied after the female had acquired spermatial 

 organs, or on the other hand that, as in many 

 other groups of plants, a hermaphrodite con- 

 dition was primitive and segregation a later 

 development. 



Amorphomyces Falagriae may be taken as 

 an example of a dioecious form which shows 

 also several other peculiarities. The spores are 

 unique amongst those of Laboulbenialesin being 

 aseptate (fig. 142). The difference between the 

 spores producing male and female plants is slight 

 at first but becomes very apparent on germi- 

 nation. In each case the spore divides into 

 three superposed cells (fig. 143 a), in the male the 

 terminal cell elongates and forms a single male 

 organ liberatingendogenous sperms. The second 

 cell maybe regarded as the basal cell of this struc- 

 ture and the lowest as a unicellular receptacle, 

 or they may be held to constitute together a 

 two-celled receptacle. There are no appendages. 

 In the female the lowest cell, which may 

 become partly divided, forms the receptacle, the 

 next above gives rise to the perithecial wall 

 and the terminal cell to the female organ proper. 

 The perithecium and its contents are therefore 

 here terminal, a state of affairs not met with 

 elsewhere in the group. The terminal cell divides 

 in the usual way to form an oogonium, a tricho- 

 phoric cell and a trichogyne ; the latter is short 

 and branching (fig. 143 £). The development 

 of the perithecium (fig. 144) seems fairly typical 

 and the asci apparently contain four spores. 



Fig. [41. Stigmatomyces Sarco- \ n 1912, Faull published an account of the 



phagae Thaxter; male and her- . . 



n. aphrodite individuals, x -.do; cytology of two species of Laboulbema, L. chaeto- 

 after Thaxter. phora, and L. Gyri.nida.rum. Both occur on the 



same host, and could not be distinguished in the young stages. Both are 



parthenogenetic, no male cells being formed. 



