V] 



LABOULBENIALES 



177 



fig. 136/, and from these asci bud out, arising in a more or less distinctly 

 double row (fig. 139 a). Some variation occurs in different species in the later 

 divisions and in the number of ascogenic cells. In Polyascomyces (fig. 140) 

 more than thirty are present, covering a basal area from which numerous asci 

 bud upwards, so that the condition approximates that in other Ascomy- 

 cetes. FauU describes the ascogenic cells as binucleate, each containing two 



Fig. 139. Stigmatomyces Baeri Peyritsch; a. young 

 asci ; b. ascus containing four spores ; c. mass of 

 spores in perithecium ; after Thaxter. 



Fig. 140. Polyascomyces Tricho- 

 phyae Thaxter; after Thaxter. 



nuclei which undergo conjugate division whenever an ascus is formed. As 

 a result the young ascus is binucleate and nuclear fusion followed by three 

 divisions takes place in the usual way. As a rule four only of the eight 

 nuclei function; the spores are produced in a manner quite characteristic 

 of the Ascomycetes, generally. In the ascus they are usually dispiosed more 

 or less definitely in pairs and the members of a pair are discharged together 

 from the perithecium and germinate side by side. 



In monoecious species one member of a spore pair may frequently 

 produce a smaller and weaker individual than the other, while in Laboulbenia 

 infiata the atrophy of one at an early stage of development is a regular 

 phenomenon. In Stigmatojnyces Sarcophagae the smaller individual is uni- 

 sexual, producing only male cells, while the larger is hermaphrodite (fig. 141). 



In dioecious species the paired spores are of rather different sizes. The 

 smaller spore gives rise to a ma"le plant, the larger to a female, so that by 

 their association at a point of contact with the host a condition essential 

 for the perpetuation of such species is secured. The cytological changes by 

 which this segregation of sex is brought about between the members of a 

 pair should be of great interest and demand investigation. 



G.-V. 



