1920] A Littlp: Known Vetch Disease 75 



Morphology of Protocoronospora nigricans 



As was indicated in the preliminary accounts by Atkinson and 

 Edgerton, this fungns presents some very interesting .structural fea- 

 tures. They call attention, furthermore, to the fact that the gross 

 appearance of the disease, the character of the fruit body, the pale 

 pink or flesh color of the spores in mass, and their appearance when 

 hastily examined under the microscope suggest the genus Gloespor- 

 ium. Since, however, they found that the spores are borne at the 

 apices of the conidiophores not singly, but in whorls and that these 

 spores on germination bud in yeast-like fashion, characters not pos- 

 sessed by anthracnoses, they believed that the fungus resembled most 

 nearly, the thelephoraceous genus, Corticium, and consequently placed 

 it there in their provisional diagnosis. They did not find opportunity, 

 however, to make a critical study of its morphology. 



Methods — In the present investigation, use was made of cultures. 

 of fresh material and of appropriately fixed and stained microtome 

 sections. For the latter purpose, portions of stems, pods, and leaves 

 were fixed in medium strength chromo-acetic acid solution and stained 

 with Flemming's triple stain according to the shortened method rec- 

 ommended by Harper. The most satisfactory preparations showing 

 the cytological features were secured when safranin was allowed to 

 act 1-2 minutes, gentian violet 10-20 minutes and orange G. 20-30 sec- 

 onds. Many of the details of the manner of penetration of the host 

 and of the development and structure of the acervuli could be sat- 

 isfactorily studied by microscopic examination of the epidermis 

 stripped from fresh material. 



The germination of the conidia and their development into colonies 

 could be followed by repeated examinations of marked conidia planted 

 upon the surface of hardened agar plate cultures. For this purpose, 

 conidia were transferred from a lesion to a drop of sterile water on 

 a microscpoic slide. A loopful of this suspension of conidia was trans- 

 ferred to one edge of the agar plate and spread over its surface with 

 a zigzag stroke toward the opposite edge. No effort was made to 

 sterilize the surface of the lesion and in consequence mixed cultures 

 containing bacteria were always secured. The bacteria and conidia 

 were sufficiently well separated toward the ultimate end of the stroke, 

 however, to permit the isolation of single spore cultures or their de- 

 velopment and study in situ. 



