PAPERS ON BOTANY 149 



specks are cell formations, wiiich have to do with repro- 

 duction, and will be discussed under the next heading. 



A cross section of the blotch mycelium (Fig. 33), shows 

 its superficial nature, and the characteristically irregular 

 looping and interlacing of the h^-phal threads, some of 

 which are darker in color than the others. 



Pycnidia. The pycnidia are scattered throughout the 

 thallus. Though often indistinct to the naked eye, they 

 are easily discernable, individually, Mdth a magnification 

 of ten diameters. They are usually found to be separate, 

 though occasionally two or three are so closely pressed 

 together as to appear united. Their presence intensifies 

 the dark, almost black, appearance of the blotched areas. 

 On apple fruit they are often very numerous, averaging 

 about 1,000 per square centimeter. This number is con- 

 siderably greater than the corresponding one for the 

 same unit of area on apple bark. Mature spore-bearing 

 pycnidia were very rarely found. 



Typical pycnidia (Figs. 10, 13) measure, when mature, 

 about 20-40^ in thickness, and 70-100," in diameter, and 

 are dimidiate, i. e.. as seen from above, they present an 

 approximately circular contour ; in cross section they are 

 found to be flattened at the base and \ri\\\ a top uniformly 

 rounded. 



They appear under the high power as closely tangled, 

 dense, reticulate masses of fine mycelial threads, with 

 h^i^hae extending away in several directions (Fig. 30). 

 Xo ostiole has been observed, its purpose being served 

 by an aperture of a different nature, the opening of which 

 begins with the appearance of a pale spot at or near the 

 central region of the pycnidium. Later stages show the 

 breaking down of the cells in this region, then one or more 

 cracks appear, and fragments drop out, leaving a large, 

 more or less jagged opening (Fig. 22). 



Within the pycnidimn are borne conidia with par- 

 aphyses. The tissue, of which the interior of the 

 pycnidium is composed, is gelatinous, as are the conidia 

 and paraphyses, which are separated with difiiculty after 

 being forced from the pycnidium (Fig. 21). 



