V] 



LABOULBENIALES 



171 



LABOULBENIALES 



The group Laboulbeniales includes some six hundred species arranged 

 in over fifty genera. All are minute external parasites on insects, chiefly on 

 members of the Coleoptera. They appear to do but little injury to the host, 

 inducing at most a slight irritation but never causing death; indeed their own 

 existence depends on that of the insect to which they are attached since, 

 unlike many other fungi, their life ends with that of their host. 



The Laboulbeniales are all of fairly simple structure (fig. 130) and show 

 an underlying similarity of type. In all cases the vegetative part consists of 

 a receptacle, usually two-celled, attached to the integument of the host by 

 a blackened base or foot. From the receptacle grow out filamentous appen- 

 dages on or among which the male organs are produced and, with a few 

 exceptions, the receptacle of the same individual also gives rise to a female 

 organ from which a perithecium liberating ascospores is eventually developed. 



The plant is covered by a thin, homogeneous membrane which is ex- 

 ceedingly tough and impervious and is developed from the gelatinous coat 

 of the spore ; it efficiently protects the cells from desiccation. 



Within this envelope the cell walls (except those of the receptive parts 

 of the trichogyne and of the internal cells of the perithecium) are very thick 

 and laminated. In certain cases, and especially in the genus Laboulbenia, 

 they are traversed by fibrillae which arise from the innermost wall layer 

 and are attached to the inner surface of the envelope. The cells are uni- 

 nucleate (fig. 131) with rather dense, granular or reticulate cytoplasm and 



Fig. 130. 



; triordinata Thaxter ; x 135 ; 

 after Thaxter. 



Fig. 131. Laboulbenia chaetophora 

 young perithecium and triclio- 

 gyne, x 360 ; after Faull. 



