264 



CONCLUSIONS DRAWN FRO.M THE SYSTEMATIC STUDY. 



Comparison of this geuiis with others of tlie order has lead us to be- 

 lieve that Stenionitis represents the most perfect differentiation and spe- 

 cialization of the Stemonitaceae. Next in oi'der l)elow it stands Coma- 

 tricha, from whicli 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 sti'ucture occiu-ring 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 remarkalile. Be- 

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

 a. like perfecting of spore markings, so tliat in a species presenting the l)est 

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

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

 tural development, pamllel to tlie above, is to be seen in tlie 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 tlie iiuier 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 tlie height of 

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

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

 same species is common. But in general we think it may 1>e safely said 

 that the tendency Is toward taller and larger sporangia, with tlie increase 

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

 futtu'e investigation will probably reveal a like gradation. 



Upon the discovery of this gradual and parallel development of certain 

 structures, it occurred 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 lie the most convenient, l)tit might, at tlie same time, 

 repx^esent the natural sequence of the species in the genus. Of course 

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

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

 as the primary liasis 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. 



