DAMPING OFF. 261 



a different species from the V. dianthi, and the name V. leucotricha 

 is here proposed for it. 



Pure cultures were then started on bean and vetch stems and in 

 a few days the characteristic stroma with the setae were developed 

 in profusion on the surface of the stems. With the conidia from 

 one of these cultures pure dilution cultures were made on April 

 2oth. Instead of pouring a few drops of the first dilution into the 

 second and from this into the third as I usually do with fungi 

 having large conidia, the second and third dilutions were made 

 by transferring with a double and twisted platinum needle. Plate 

 number i and 2 were sufficiently separated for the study of colony 

 characteristics and for photographing natural size. The colonies 

 grow rather slowly and the plate No. 2 was ready for photograph- 

 ing on the 25th, and No. 3 on the 27th. In No. 2 the colonies 

 were quite numerous and consequently rather small, from 4-6 

 mm. in diameter, while those in plate No. 3 where there were 

 only 6 colonies were on the 2yth 10 mm. in diameter. The col- 

 ony steadily develops a thin and nearly circular weft marked by 

 numerous fine radiating lines which because of the exceeding 

 thinness of the weft are visible over the entire colony as it ages. 

 There are quite regularly more dense radiating lines caused by 

 the overlapping of certain radiating areas, and the margin shows 

 a tendency to form roundish angles. The growth is quite sensi- 

 tive to periodic changes in temperature which occur between 

 night and day, as shown by the several concentric lines which are 

 quite pronounced on the colony. At the center of the colony 

 there is developed quite a compact stroma which is very much 

 like that on a more solid substratum, like the stems of the vetch 

 or bean. This stroma may be quite extensive and irregular in 

 outline with a few outlying smaller and scattered ones, or there 

 may be quite a large number of them at the center of the colony, 

 the larger ones of course nearer the center and the smaller ones at 

 the periphery. These individual stromata are so far like those 

 developed in solid substrata, either in nature or culture tubes, 

 that they are margined with the characteristic setae. A photo- 

 graph of several of these growing in the agar in a Petrie dish is 

 shown in fig. 52, plate VI, left upper corner. The photograph 

 was taken from directly above and is magnified about 60 diameters. 



In a few days after the appearance of the colonies the basidia 



