242 BOTANICAL GAZETTE [September 



a generic separation desirable. In only one species, M. repens, 

 does it assume a repent habit, such as is illustrated in fig. 6, and 

 in this instance only on the host's wing. This may be due in part 

 to the less nutritious character of the substratum; yet other species, 

 when they occur in the same situation, retain their isolated tuft- 

 like habit, which is also characteristic of this species when it occurs 

 on the body or legs of its host (fig. 8) . 



The spores, which always resemble those of Alternaria in general 

 form, differ from those of Macros porium in being inseparable from 

 the sporophore, a portion of which breaks off with them, and in the 

 characteristic differentiation of the central portion, which consists 

 of two similar flattened cells; which, in all the species except M. 

 repens, become divided once transversely before the appearance 

 of a few longitudinal septa. The four tiers of small cells which 

 result are usually clearly distinguishable, as is indicated in fig. 4; 

 and with the exception of M. repens, the vegetative portion is 

 hardly developed; a tuft of more or less divergent elements being 

 attached by a compact blackened base, which may or may not 

 be associated with slight rhizoid-like outgrowths. The body of the 

 spore is flattened, so that when it is viewed edgewise, it is often 

 hardly broader than the stalk and tip. Both the spores and their 

 stalks are brittle, and it seems probable from the appearance of 

 very small plants which are sometimes found growing on hairs or 

 spines, that propagation may be effected by small detached frag- 

 ments as well as by whole spores, from which the larger groups 

 appear to arise; although in the latter case, it is seldom possible 

 to determine definitely that a portion of the general blackened 

 base is made up of the old spore body. The spurlike processes 

 which may arise in some species (figs. 9), either from the stalk 

 just below the spore, or from the slender termination of the latter, 

 sometimes in both positions (figs. 4 and 5), are characteristic, but 

 are not present invariably or in all the species. 



The body of the spore, sometimes also its termination and the 

 whole or a portion of the stalk and sterile elements, if they are 

 present, are irregularly mottled or lined by a somewhat darker 

 incrustation which gives the surface a somewhat roughened appear- 

 ance. This superficial modification tends to obliterate the longi- 



