Parallel Mutations. 51 



very remote indeed. A minute but distinctive difference is in the 

 large hairs of the calyx. On the hud-cone they are strongly 

 ascending except around the top of the hypanthium where they 

 are retrorse or perpendicular. 



The cruciate form from Jaffrey, New Hampshire, is described 

 by Bartlett, in the same paper, under the name CE. Robinsonii. 

 There is said to be " enough likeness between (E. venosa and OS. 

 Robinsonii, so that a close relationship between them seems not 

 unlikely." The differences from venosa are chiefly in the smaller 

 size of Robinsonii, its more sharply dentate leaves, narrower bracts, 

 longer more slender buds with dense erect viscid puberulence, and 

 shorter calyx tips. The range of variation in bud length overlaps, 

 however, and most of the differences are only obvious in the living 

 plants. These two forms evidently represent closely allied 

 elementary species rather than species in the Linnean sense. 

 Both having cruciate flowers, one from New York State, and the 

 other from New Hampshire, in the absence of local species of which 

 they could be varieties the common character of cruciateness 

 probably originated some time ago, and we may suppose that the 

 series of small differences which distinguish the two species 

 throughout have originated since. 



Contrasted with these forms, in which the cruciate character 

 appears to be of relatively ancient origin, is another cruciate species, 

 CE. stenopetala Bicknell, described from Nantucket Island in 1914. 

 It is closely allied to the broad-petalled species CE. Oakesiana Wats., 

 from which it is probably descended. Yet the two have diverged 

 in certain respects. In the case of CE. biennis leptomeres, which 

 apparently is still appearing as a mutation from bienms in Holland, 

 the single difference in the flowers is unaccompanied by any other 

 differences. This series is a most instructive one as a basis for 

 contrasting the conspicuous unit difference of sudden and repeated 

 origin, with the other smaller differences relating to all parts of the 

 plant, by which the species have subsequently become differentiated. 

 Whether the same type of evolutionary change is represented in 

 both cases, is a matter worthy of close and prolonged study. By 

 comparison and crossing of these cruciate forms, definite evidence 

 might be obtained on this point. In many cases such elementary 

 species differ from each other in physiological characters or 

 methods of reaction to environment. An intensive study should 

 make it possible to determine what relation if any these physiological 

 and morphological differences bear to each other. 



