﻿GATES— PAIRS OF SPECIES 



185 



four mutations. The various other mutants and combinations 

 we may suppose to have been eliminated by selection or by their 

 own instability. The fact that C. umbellulata is odorous, while 

 C. borealis has no marked odor, is by no means unique. Similar 

 cases occur in various other genera, including Oenothera and the 

 variation in Spiranthes cernua recently mentioned. They find 

 their parallel and no doubt their basis in organic chemistry, where 

 a change of an atom or even a rearrangement of the atoms in a 

 molecule produces an odorous compound from an odorless one. 



Streptopus amplexifolius (L.) DC. and S. roseus Michx. 



In comparing these well known species we find a more marked 

 series of differences. As regards distribution, S. amplexifolius is 

 boreal and circumpolar, occurring in Europe and Northern Asia, 

 Greenland, Newfoundland, Labrador to Alaska, and south to 

 North Carolina and California. S. roseus is not found in Europe 

 or Asia, but occurs from Newfoundland and Labrador to Alaska, 

 and southward to North Carolina and Oregon. 



Fernald 8 has made a careful study of the differences between 

 the two species, which may be briefly set forth as follows: 



S. amplexifolius (fig. 4) S. roseus (fig. 5) 



Stem whitish and glabrous Stem greenish and usually 



Leaves strongly glaucous, Leaves green, scarcely am- 

 amplexicaul, glabrous plexicaul, conspicuously 



Perianth segments spreading Perianth segments slightly 

 widely and quickly recurved divergent, only the tips 



Anthers lance-subulate, entire, Anthers narrow-ovate, bifid, 



Stigma subentire or merely Mil" 

 shaUow-lobed 



These two common and widespread species thus exhibit a 

 mber of conspicuous unit differences, which are unlike the differ- 

 :es in the pair of species of Clinlonia previously examined. The 



" I kkxai.d, M. I.., The genus Streptopus in eastern America. Rhodora 8:69-71. 



