﻿GATES— PAIRS OF SPECIES 



from the moment of their origin, just as certain chemicals will 

 react with each other while others will not. 



It seems highly improbable that the specific differences between 

 S. amplexifolius and 5. roseus are directly of selective value to their 

 possessors. We are beginning to learn that natural selection must 

 often act in more roundabout ways, through sterility, etc., and not 

 directly as arbitrator between the possessors of one or other of a 

 pair of differential characters. The character differences them- 

 selves must often be innocuous as regards the economy of the plant. 



Maianthemum dilatatum (Wood) Nelson and Macbride 10 



AND M. CANADENSE DESF. 



The genus Maianthemum has been variously considered as 

 having one, two, or three species. M. bifolia DC. in Europe and 

 M . canadense Desf . in North America are now regarded as distinct, 

 and a giant form variously known as var. kamtschaticum Gmel. 

 and var. dilatatum Wood has been attached to the former species. 

 It is clear that M. bifolium and M. canadense are distinct, and there 

 seems no doubt that this " variety" should be recognized as a 

 third species. Nuttall first recognized it as such. It is found in 

 Western America, from California northward to Alaska, and 

 apparently in adjacent Asia. 



This species is essentially a giant M . canadense except that the 

 leaves have nearly the peculiar shape of M. bifolium. In view of 

 our knowledge of the relation between Oenothera Lamarckiann and 

 O. gigas, it would not be at all surprising if this also proved to be 

 tetraploid. It is to be hoped that some one will make a cytological 

 comparison of these two species. Their differences are shown in 

 fig. 6. M. dilatatum is not only stouter, with larger inflorescence 

 and larger leaves, but the leaves also differ in shape, being broader 

 and with conspicuous basal lobes. This is not at all incompatible 

 with tetraploidy, as we know from the case of Oenothera gigas. in 

 which the leaves are very much broader and obtuse pointed. 



^ 10 Maianthemum dilatatum (Wood) Nelson and Macbride, Bot. Gaz. 61:30. 1916. 



dilatata Nutt. ex Baker, Jour. Linn. Soc. 14:563. 1875; Convallaria bifolia var. 

 kamtschaticum Gmel. Cham, and Schlecht. Linnaea 6:587. 1831. 



