264 



OONOLUSIONS DRAWN FROM THE SYSTEMATIC STUDY. 



Gomparisou of this genus with otliers of the order has lead us to be- 

 lieve that Stemouitis represents tlie most perfect differentiation and spe- 

 cialization of the Stemonitaceae. Next in order below it stands Coma- 

 tricha, from which the former is not very easily separated, as its lowest 

 forms are much like the higher forms of Comatricha, only its one char- 

 acteristic structure, the superficial net, serving to distinguish it. 



This superficial net is peculiar in several respects. In the first place, 

 it is almost the only example of such a structure occurring among the 

 slime moulds, although a slight indication of such a structure may be 

 noted in the higher forms of Comatricha. In the second place, its gradual 

 development and perfection in Stemonitis is indeed very remarkable. Be- 

 sides, this gradual perfecting of net structure is found to correspond with 

 a like perfecting of spore markings, so that in a species presenting the best 

 development of this superficial net we find the most specialized forms of 

 spore marking. Another and almost equally interesting gradation in struc- 

 tural development, parallel to the above, is to be seen in the inner 

 or supporting network of the capillitium. Although presenting some ex- 

 ceptions, this shows on the whole a tendency to a steady reduction in the 

 number of threads of the inner network and a thickening of the resulting 

 ones. In the species we have studied there was noted, corresponding to 

 the differentiation just described, a gradual increase in the height of 

 sporangia. An examination of Macbride's listed species present some 

 interesting exceptions. A wide variation in height of sporangia of the 

 same species is common. But in general we think it may be safely said 

 that the tendency is toward taller and larger sporangia, with the increase 

 in complexity of the contained parts. There are other structures that upon 

 future investigation will probably reveal a like gradation. 



Upon the discoveiy of this gradual and parallel development of certain 

 structures, it occun-ed to us that a classification of the species of this 

 genus, upon the basis of the development of some of these structures, 

 would not only be the most convenient, but might, at the same time, 

 represent the natural sequence of the species in the genus. Of course 

 that structure which showed this development, and at the same time 

 proved most constant in the different species, was the one to be chosen 

 as the primary basis of classification. Careful investigation of a large 

 number of individuals of each species showed that spore markings pri- 

 marily, with size and color secondarily, was the structure to be selected. 



