290 A TEXTBOOK OF THEORETICAL BOTANY 



e.g., Xylaria, the size of these stromata is considerably greater than in the 

 type we have selected. The family is essentially a tropical one, and the 

 genera attain their highest development under such conditions. 



Laboulbeniales 



The Laboulbeniales are parasitic Ascomycetes living externally on insects. 

 Though they may produce slight irritation they never cause the death of 

 the host, in fact their survival ultimately depends upon the continued life of 

 the insect, since with the death of the host they too are killed. 



Though the members are small in size and consist merely of a filament 

 of cells, the group is of great interest because of the structure of the repro- 

 ductive organs. These consist of an ascogonium provided with a terminal 

 trichogyne, and antheridia each of which liberates a single non-motile 

 spermatium. These spermatia are carried passively to the trichogyne to 

 which they become attached. As a resuh of fertilization a diploid nucleus 

 is formed in the ascogonium which develops into an ascus from which four 

 ascospores are ultimately produced. 



We shall consider as our example of the group Stigmatomyces haeri. 



t 



X.omyct% 



Stigmatomyces haeri 



The organism occurs on the common House Fly {Miisca domestica) 

 (Fig. 284) and was first investigated from material collected in Vienna. 



The vegetative part of the organism, which is termed the receptacle, 

 consists of the two superimposed cells of the ascospore, the upper cell giving 



rise to a multicellular appendage 

 on which the antheridia are de- 

 veloped unilaterally. The lower 

 cell of the receptacle divides ob- 

 liquely and the cell thus cut off de- 

 velops laterally into a perithecium. 

 The perithecium is brownish- 

 vellow in colour and contains a 

 single row of cells, terminating in 

 a single-celled trichogyne. After 

 fertilization a single ascus is formed 

 from the lowest cell but one of the 

 filament and four ascospores are 

 produced which are each divided 

 into two cells. 



Our knowledge of the develop- 

 ment of this organism is due to 

 Fig. 284. — Stiematomvces spiralis. Habit of , 1 r --ni , 1 1 -i 



growth of fungus'on the body of a House the WOrk of Thaxter, who, while 



Fly. working in the Harvard labora- 



From a photograph from Thaxter' s original preparation in t^iriVc in Pi^mKriHaP Ma«;<5 TTRA 

 the Farlow Herbarium taken by Professor Weston.) tOHeS m <>^amDnUge, iVldbb., U.O./^., 



