﻿iqi6] GATES— PAIRS OF SPECIES igl 



standpoint their occurrence in no way obscures the relationship of 

 the two species; and the same is true of all other tetraploid species 

 when they come to be known as such. 



There seems to be a tacit recognition of M. dilatatum as peculi- 

 arly related to one of the other species, for it has been classed as a 

 variety, although it is easily as distinct from either M. hi folium 

 or M. canadense as these are from each other. 



If this supposition with regard to this pair of species of Maian- 

 themum proves to be correct, then their relationship to each other 

 is very different from that found in our pairs of Clintonia or of 

 Streptopus, for in the latter cases we found it necessary to assume 

 that pairs had arisen through several divergent steps, accompanied 

 no doubt by free intercrossing of the various forms produced by 

 these successive mutations. In M aiantkemum, however, we assume 

 one species to have given rise directly to the other, and any inter- 

 mediates to have arisen later through crossing. 



The specimens of M. dilatatum examined show little variation 

 in foliage, and this may perhaps be taken as an indication that the 

 species is not tetraploid, although in any case its cells may be 

 expected to be conspicuously larger than in M. bifolium or M. 

 canadense™ Since its leaf shape agrees with that of M. bifolium. 

 it is probably best considered as a giant of that species, although 

 it agrees with M. canadense in being glabrous. M. dilatation 

 thus bears features of both the other species, although it is entirely 

 distinct from either. We may reasonably assume that it originated 

 from a glabrous variety of M. bifolium, which had itself arisen 

 from the type through a negative mutation in loss of pubescence. 



Ranunculus abortivus L. and R. allegheniensis Britt. 

 My attention was directed to this pair of species by Dr. J. M. 

 Greenman. R. abortivus has much the wider range, occurring 

 from Labrador and Nova Scotia to Manitoba, and south to Florida. 

 Arkansas, and Colorado; while R. allegheniensis, a segregate 



geners makes one doubt the possibility that they are all cell giants. Their greater 

 vigor may result perhaps from an effect of climate. Only a cytologic^! examination 



