.16 BULLETIN 727, U. S. DEPARTMENT OF AGRICULTURE. 



Halsted (23), Prillieux and Delacroix (39), Stoneman (50), Sheldon 

 (46), Potebnia (38), Shear and Wood (45), and Eriksson (16). 

 Potebnia gives an especially good description. 



Mycelium. — The mycelial characters vary greatly with age and 

 substratum. At first the mycelium is colorless, thin walled, septate, 

 and quite uniformly cylindrical. Many of the cells later increase in 

 diameter about threefold and tend to become thick walled and dark 

 brown in color, resembling intercalary chlamydospores. Oil drops 

 are commonly present in old mycelium. In culture, the mycelium is 

 first colorless, then pink, and finally black. In host tissue the pink 

 coloration is sometimes seen, and the blackening is quite commonly 

 produced in fruit lesions. The brown, thick-walled, large-celled 

 mycelium occurs commonly in host tissue. 



Acervuli. — The mycelial filaments tend to aggregate at certain 

 points, branch, intertwine, and send out a palisade layer of short 

 colorless conidiophores. The extent of stromatal development pre- 

 vious to sporulation varies greatly and is apparently greater in cul- 

 ture than in host tissue. The color of this stromatic tissue is brown 

 or black. 



Setse. — Scattered about among the conidiophores are the long 2-3 

 septate, brown, thick-walled bristles, or setse, varying in length 

 from 90 to 120 m and tapering toward a blunt point. The setse may 

 be much longer under certain conditions. The number in each 

 acervulus varies greatly and is given as high as 24 to 36 by Potebnia. 



Spores. — From the tips of the conidiophores the spores are budded 

 off apically, one at a time, and pile up in a pink slimy heap on top 

 of the acervulus. The spores are embedded in a sticky water- 

 soluble matrix, and the heaps are often as high as the setae, the 

 latter apparently serving as supports to hold the spore mass in 

 place. The spores are one celled, hyaline, oblong or ovate-oblong, 

 and slightly pointed at one end. Spores vary considerably in shape. 

 Their size is about 13 to 19 n by 4 to 6 ju. Usually two or three 

 vacuoles are present. The spores are pink in mass. 



Sclerotial bodies. — These are usually the result of the further de- 

 velopment of the stromata or bases of the acervuli, in which the 

 whole mass becomes considerably enlarged and black in color. The 

 size of these sclerotial masses varies greatly, as does also the degree 

 of their development. Sclerotial masses are formed abundantly in 

 culture and in fruit lesions. Sheldon (46) describes these in detail. 

 In culture the spore mass may dry down and remain as part of the 

 protruding sclerotium. In fruit lesions the spores are washed away 

 and only the black stroma remains, forming the black spots in the 

 fruit lesions previously described. 



Apyressoria. — Normally, a germinating spore on a firm or hard 

 substratum forms an appressorium at the tip of each germ tube or 



