690 



Journal of Agricultural Research 



Vol. XX, No. 9 



viable conidia are placed on the surface of onion bulbs, appressoria or 

 chlamydospores are formed in contact with the scale. Later they send 

 out germ tubes which penetrate the host. They are also commonly found 

 within the tissue of affected scales. 



Acervuli. — The fruiting bodies are formed on the stromata which 

 develop beneath the cuticle of the host. Short, hyaline conidiophores 

 form in a palisade layer and rupture the cuticle of the host (fig. 2). One 

 to several acervuli form on a single stroma. In the study of the morphol- 

 ogy of the fruiting body the writer has found no evidence of a closed or 

 partially closed receptacle, as described originally by Berkeley (4). Its 

 true nature is more nearly in accord with the work of Stoneman (32), 

 who found not a pycnidium but an open fruiting body. 



Fig. 2. — Acervulus of Collelotrichum circinans on artificially inoculated onion scale. Note the develop- 

 ment of the stroma in the subcuticular wall and the rupture of the cuticle by the formation of the 

 palisade layer of the sporiferous hyphae. Camera-lucida outline. X 265. 



Setae. — Scattered throughout the acervulus are numerous setae 

 arising from the basal stroma. They are thick-walled, dark-colored, 

 o to 3 septate, upwardly attenuate, and 80 to 315 microns in length. 



Conidia. — The conidia are borne acrogenously, being budded off one 

 at a time. They are fusiform, continuous, hyaline to slightly ochraceous, 

 somewhat curved, and obtuse at the very apex. Typically one prominent 

 vacuole is present in the center of the conidium, but under some conditions 

 the cytoplasm may contain many large vacuoles. As the spores are 

 budded off from the conidiophores they form a cream-colored, somewhat 

 mucilaginous mass on the top of the fruiting body. The spores vary 

 from 14 to 30 microns in length and from 3 to 6 microns in width. A large 

 majority, however, fall within the limits of 18 to 28 microns by 3 to 4 

 microns. They germinate usually by one, but occasionally by two or 



