160 THE ASCOMYCETFS 



Venicilliinn iiotatiiTn is used in the preparation of the best-known 

 antibiotic, peniciUin. 



Thielavia. The several species of Thielavia appear to be 

 closely related to Aspergillus and Penicillium. The best-known 

 member is T. basicola, considered by Gilbert (1909) and others 

 the cause of black-root rot of tobacco and various leguminous 

 plants. iMcCormick (1925) presented evidence, however, that 

 T. basicola is not genetically connected with a conidium- and 

 chlamydospore-producing fungus, Thielaviopsis basicola, with 

 which it is associated in nature. This genetic relationship, or 

 lack of it, might well be given further consideration. 



The development of ascocarps in Thielavia terricola and T. 

 sepedojiium was studied by Emmons (1932). Cultures from 

 single spores give rise to ascocarps, which begin as hyphal coils. 

 The distal ends of these hyphae recurve, and cross walls are 

 laid down. The tip or ultimate cell of each is just beyond the 

 one that makes up the crook or crosier. This crosier is therefore 

 penultimate. Each cell of the ascogenous hypha is uninucleate 

 except the penultimate one, which has two nuclei. Such binu- 

 cleate cells enlarge, and each becomes an ascus. During this 

 process there is first a fusion of the two nuclei, f ollow^ed by three 

 nuclear divisions, and the cutting out of ascospores. 



The production of so-called "endoconidia" w^as studied by 

 Brierley (1915). He found that the first conidia are formed 

 endogenously, but that the tip of the conidiophore bursts to lib- 

 erate these conidia. The conidium-producing cell is therefore 

 endogenous and produces chains of conidia. 



Onygenaceae 



One genus, Onygena, with 6 species comprises this family. Its 

 habitat is hair, hoofs, fur, feathers, horns, claw s, and other animal 

 materials. The ascocarps of 4 species are stalked and capitate. 

 A powdery coating of gemmae may cover the young heads. 

 When they are mature, sterile hairs occur, interspersed with the 

 asci, which disintegrate. The heads open irregularly, so that the 

 ascocarps look like tiny puffballs or else like sporangia of slime 

 molds. Little is known about the developmental history of Ony- 

 gena beyond the information contributed long ago by Ward 

 (1899). 



