12 ILLINOIS BIOLOGICAL MONOGRAPHS [178 



but central parts are regularly radiate. At first this disk is devoid of per- 

 ithecia but they soon develop, one or two, later more as the subicle en- 

 larges. Thus old colonies by both coalescence and enlargement may have 

 well over a hundred perithecia and measure nearly a centimeter in diameter. 

 As the perithecia develop the subicle under them thickens to true stromatic 

 character, 80 to 15()m thick. (Figure 14) In large colonies the radiate 

 subicle enlarges to present a margin about a millimeter wide around the 

 colony. In certain old colonies the radiate subicle is not in evidence due 

 to the fact that it flakes ofT. The central foot is 80 to 90^ thick and 150^ 

 long and is composed of cells of different shape, arrangement and staining 

 reaction than that of the other cells of the stroma i. e. they are arranged 

 parallel, lengthwise of the a.xis of the foot, and under Pianese stain are red, 

 while the other stroma cells are irregularly arranged or preponderantly at 

 right angles to the a.xis of the foot and do not stain as above stated (Figures 

 7, 11.) The wall surrounding the locules is black, about 36/i thick and is 

 lined by a hyaline layer also about idn thick from which, in the basal por- 

 tion, the asci arise (Figure 12). Frequently a large stroma is found attached 

 to the hypostroma by several feet (Figure 14). Such may be regarded as 

 composites of several individuals each with a central fool, rather than as 

 one individual with many places of attachment. 



The locules, stroma, foot, and hypostroma are typically Dothideaceous 

 in character; the flat radiate subicle is typically Microthyriaceous. Dis- 

 regardmg the radiate subicle the fungus falls readily within the Dothideaceae 

 and the centrally fastened stroma places it as typically of the Coccoideae 

 and in rather close agreement with the genus Microcyclus. 



Taking cognizance of the radiate, subicle, and attempting to place the 

 fungus in the Microthyriaceae, it shows nearest relationship to the Poly- 

 stomelleae with no genus of which does it agree. In the Meliolineae one 

 is reminded of Actinodothis by the radiation and by the stromata but our 

 fungus differs much from this genus in spores and mycelium. 



The fungus thus shows kinship with the three groups and appears to be 

 most closely related to the Dothideaceae in which family I place it. It 

 evidently represents a transition form between the Microthyriaceae and 

 the Dothids. The course of evolution appears to me probably to have been 

 somewhat as follows: A primitive Microthyriaceous fungus with haustoria 

 reaching into the epidermis developed an extensive hypostroma connected 

 with the superficial mycelium at one central point. The habit of forming 

 a radiating disk around the point of central fastening then appeared. So 

 far in its history the fungus was Microthyriaceous. Now begins the evolu- 

 tion of the stroma by thickening of the central region of the radiate disk and 

 the fungus becomes Dothideaceous. As the stroma-habit developed the 

 radiate habit of the Microthyriaceae appears to have regressed as is evi- 

 denced by the irregularity of the radiation in the present form and by the 



