224 ' BOTANICAL GAZETTE [September 



characterization of the genus, it has no fruit bodies, but consists 

 only of sterile mycelium. 



The rose fungus evidently, then, does not possess the characters 

 of a typical Marsonia, nor does it agree with the original charac- 

 terization of Actinonema. Whether these differences are worthy of 

 good generic rank, separating it from both these genera, is a 

 matter for consideration. 



Development of the ascigerous stage 



During the autumn of 19 10, leaves attacked by the conidial 

 stage were collected and placed in wire cages to winter out of 

 doors. When some of these leaves were brought to the laboratory 

 early in April and examined, shield-shaped structures suggestive 

 of the perithecia of the Microthyriaceae were found to be present. 

 At this time, however, no spores had been developed. Fig. 2 

 shows one of these perithecia as seen in surface view. Such prepa- 

 rations were made by stripping off the epidermis of the leaf together 

 with the perithecia. By April 27 these perithecia had matured 

 and were found to possess characters similar to the genus Asterella, 

 a genus apparently including heterogeneous elements. 



For the study of the development of the perithecia, material 

 was killed in Merkel's fluid and stained with Flemming's triple 

 stain. By killing material at different times during a period of 

 three weeks, many of the developmental stages were obtained. 

 Not all perithecia on the same leaf are in the same stage of develop- 

 ment at the same time. Unfortunately the material was too far 

 advanced for the study of fertilization and the immediate subse- 

 quent development. This in itself would be a very interesting 

 study, since nothing is known of these phenomena in the Micro- 

 thyriaceae. 



The shield was found to be entirely separate in origin from 

 the tissue which gives rise to the asci. It is formed immediately 

 beneath the cuticle from the radiating strands of mycelium which 

 now are thick-walled and dark brown in color. The strands 

 themselves can be traced across the shield (fig. 4)? showing that 

 the growth begins at any point on the mycelial strand and new 

 cells are added in a centrifugal manner. In this way a more or 



