[Vol. 10 



118 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



el to the long axis of the stem. Usually the long dimension 

 to 1 ' L > t imes as great as the short one. On leaves, many of 

 the pycnidia are isodiametric, but a considerable number may be 

 found which are markedly longer in one direction. Pycnidia 

 open by a pore having a diameter of 15-25 (i (pi. 9, fig. 11), 

 through which pycnospores crowd in a steady stream for several 

 minutes when mature pycnidia are immersed in water. 



Pycnidial development has been traced macroscopically in 

 cultures on sterile soybean stems. Small stems were placed in 

 test-tubes containing moist absorbent cotton. These were 

 autoclaved and inoculated at the bases where they were in 

 contact with the moist cotton. Under these conditions, pycnidia 

 first became visible as points of whitish growth which appeared 

 somewhat translucent under a hand lens and by microscopic 

 examination were found to consist of pseudo-parenchymatic 

 tissue. At this stage they possessed a diameter of about 0.2 

 mm., had formed no spores, and appeared to contain a very small 

 quantity of liquid material. The pycnidium enlarged rapidly 

 and the wall became darkened, finally becoming black in color. 

 Simultaneously with this enlargement, hyphae apparently 

 arising from cells constituting the pycnidial wall covered the 

 pycnidium, causing it to appear white. However, upon close 

 inspection, the black pycnidial wall could be seen through this 

 white hyphal mantle, which, because of its evanescent character, 

 disappeared later, clearly revealing the black color of the pyc- 

 nidial wall. Spores appeared soon after the 0.2 mm. stage and 

 continued for a period of time as yet undetermined for individual 

 pycnidia. A height of 1 mm. and a basal diameter of half of 

 this may be attained in culture (pi. 11, fig. 1 A-C). 



The pycnosporophores are simple, slender, hyaline, non- 

 septate, tapering structures; their length varies from \}/2 to 

 3 times that of the pycnospores (fig. 1). They arise from the 

 inner layer of irregular cells of the pycnidium and constitute a 

 bright band lining its wall. Branched forms are very infrequently 

 found. 



Pycnospores are single-celled, hyaline, and usually possess 

 2 large droplets, guttulae, 1 in each end (figs. 2-3). The drop- 

 lets are not invariably present and disappear in germination. 



