l8o BIOLOGICAL LECTURES. 



ities. 1 In 1887 the late Dr. George Lawson strongly advocated the 

 validity of Link's species, 2 and this has now found support on 

 the part of Dr. Britton. 3 From this it is apparent that great 

 difficulty has been experienced in defining the specific limita- 

 tions in these cases, and it has been felt that evidence derived 

 from the internal structure of the wood might serve to deter- 

 mine the balance of evidence in one direction or the other, and 

 thus settle definitely this long-standing controversy. Recent 

 critical studies of these plants serve to show beyond all ques- 

 tion that Picea rubra must henceforth be recognized as a distinct 

 species. 



The limitations of Chamaecyparis and Cupressus, as also the 

 separation of these two groups from the closely allied Thuya, 

 have formed the basis of a long-continued discussion. The 

 difficulties met with are well indicated in the recent observation 

 of Dr. Masters when he says: "If the two genera (Thuya and 

 Cupressus) had not been so long established and so generally 

 adopted, it might have been well to have included them in one 

 genus, together with Libocedrus, as in all probability all of 

 these have been derived from a common stock. The confusion 

 this would entail in practice would, however, be so great as to 

 outweigh any advantages that would accrue from such an 

 arrangement, theoretically preferable though it might be." 4 

 As will shortly appear, there are strong reasons on anatomical 

 grounds in support of the contention thus advanced by Dr. 

 Masters for the union of Thuya and Cupressus. In the latter 

 genus we also find that it must now include the former genus, 

 Chamaecyparis, while there is likewise a further question as to 

 whether Cupressus guadalupensis and C. macrocarpa are distinct 

 species, as heretofore considered, or only forms of one species, as 

 suggested by Dr. Masters, 5 who has more recently maintained 

 that C. guadalupensis is a distinct variety of C. macrocarpa. 6 



Finally, we may refer to the great want of agreement as to 

 the relations of the Taxaceae and Coniferae. From these 



1 Gray's Manual, 1890, p. 492. 



2 "Remarks on the Distinctive Characters of the Canadian Spruces," Can. Rec. 

 Sc., VII, 162, 1896. 3 Flora of the Northern States and Canada, 1896, p. 55. 



4 Jottrnal Linn. Soc., XXXI, 313. 



6 Garden and Forest, VII, 298. * Journal Linn. Soc., XXXI, 343. 



