150 ILLINOIS ACADEMY OP SCIENCE 



In tlie accompanying diagram (Fig. 34), are sliown in 

 cross section, the relative positions of the various parts 

 of the pycniclium. The pycnicliiim (a), is seen to be en- 

 tirely above the cuticle (b), and to possess a solitary 

 subglobose locule (e). The mycelium (f) leading up to 

 the pycnidium proper, is extremely dense, and it is sel- 

 dom that its cellular structure can be recognized. It ap- 

 proaches the locule from either side, the locule being in 

 a way buttressed by the ends of the former. The locule 

 itself is surrounded by cells of irregular shape (d), 

 somewhat gelatinous in character, and thinner walled and 

 lighter in color than those of the thallus (f), individual 

 cells in the inner layer alone, being recognizable. Cellu- 

 lar structure of this nature extends above the locule, 

 making up the upper layer (c) of the pycnidium. In the 

 angles (g), made betwen the buttressing mycelium and 

 the locule, as well as along the base of the pycnidium just 

 below the locule, the cells are still lighter in color than 

 those immediately above the locule. 



Pycnidial Formation. According to DeBary (1884), 

 and Kempton (1919), pycnidia may arise by one of two 

 methods, which they designate as ' ' symphogenous " and 

 ''meristogenous": ' ' symphogenous " when the young 

 hyphal threads interlace to form at first a loose network, 

 later one gnarled and knotlike, ''meristogenous" when 

 the pycnidial primordium arises by intercalary growth 

 on one or more cells of one hyphal branch. A^ariations 

 in these two methods have also been noted, such as simple 

 and compound modes of each, or even a combination of 

 the two methods. 



The various stages in pycnidial formation in sooty 

 blotch, have been followed on apple skin by mounting 

 representative bits at different times in the year. Pycni- 

 dial development was observed to be in progress in Sep- 

 tember, but it is not usually complete until the winter is 

 over, and appears to proceed naturally on material win- 

 tering out of doors. 



Pycnidial formation in sooty blotch is usually sym- 

 phogenous (Figs. 27-30), though the behavior of the 



