V J LABOULBENIALES l?? 



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

 double row (fig. 1 39 a). Some variation occurs in different species in the later 

 divisions and in the number of ascogenic cells. In Pofyascomyces (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. Faull describes the ascogenic cells as binucleate, each containing two 



Fig- 139- Stigmatomyces Bacri 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 disposed 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 

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

 phenomenon. In Stigmatomyces 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 male 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. 



