B2 KOYAL SOCIKTY OK CANADA 



efforts to untangle tlie difliculty.* Kra.us- and Solras-LaiiUith,'' among 

 recent authorities, have done more than any others to give a clear and 

 systematic conception of the real nature and rchitions of these plants. 

 Knowlton has also summarised our knowledge of them in !-ucii a way 

 as to ailord a working basis of consich'rable value* 



Looking at tlie various (k*crij)tions of tlio internal structure of 

 the stem, one is immediately imprei?sed with the inadeiiiuicy of the 

 diagnoses and the too often loose and unscientific way in which the 

 facts lare stated, giving no adequate ground for comparison and the 

 accurate differentiation of one species from another. Thus in D. New- 

 borryi, one of the most important structural facts is entirely neglected 

 in the description of the species, while in others, the mere stiitement 

 that a certain detail is more or less like that of anoilicr sjiecies in which 

 it is poorly or inaccurately described, conveys no accurate conception 

 of the real fact,s, and forms no jjrojjcr basis for comp'-arison. 



Sudi looseness is a common fault and apju'ars even in the most 

 recent publications. The exphanation is no doubt to be found in the 

 fact that there has been no genertal revision of all the species on the 

 basis of the stem structure, but one author has copied from another 

 and in such copying there has been no direct reference to the original 

 types for purposes of verification. 



The work of Sir William Dawson, extending over half a century, 

 hias resulted in the accumulation of a large amount of material from 

 various parts of North America, the greater portion of which formed the 

 basis of published desci-iptions, but there was also a considerable 

 amount of luaterial which iuul never been fully determined. This em- 

 braced species descril)ed only in his notes, as well as others which he 

 had not attempted to describe. There were thus some species without 

 names, and others to which he had assigned specific names. ^luch of 

 this material has been found to be identical with species iilready well 

 known, while other portions embraced new species, and in such cases 

 the names employed by Sir William have been retained and are now 

 published for the first time. The accumulation of a particularly valu- 

 able collection of type material, presented an opportunity for authorita- 

 tive revision of the genus, which was not to be neglected. 



These considerations seemed to me sufficient to justify prosecution 

 of tlie work as promptly and as completely as possible, and (although it 



■ Proc. U. S. Nat. Mus., 1890, XII., 601. 

 = Schimper's Traitfi de Pal. Veg., II., 1870. 

 ' Fossil Botany, 1891, 105. 

 * Proc. U. S. Nat. Mus., 1890, XII., 601. 



