THE BASIS OF THE STEM STRUCTURE. 187 



The two genera Thuya and Cupressus are very closely con- 

 nected, and for a long time morphologists have been unable to 

 agree as to their precise limitations. The Thuya occidentalis 

 of Linnaeus and T. gigantea of Nuttall appear to have been 

 referred to this genus without exception. Cupressus thyoides 

 of Linnaeus was referred by Spach to Chamaecyparis sphae- 

 roidea, by Sprengel to Thuya sphaeroidea, and by Richard to 

 T. sphaeroidalis, a name which has been adopted by the Index 

 Kewensis as authoritative. 



Cupressus nutkaensis of Hooker, or C. nootkatensis of Lam- 

 bert, was also referred to the same genus by Trautvetter under 

 the species C. americana. By Carriere it was referred to the 

 genus Thuyopsis, and at different times to T. borealis and T. 

 cupressoides. Both Spach and Walpers referred it to the genus 

 Chamaecyparis, and Fischer also recognized the same genus, but 

 applied the specific name of C. excelsa. The most recent ruling, 

 as embodied in the Index Kewensis, indicates that Lambert's 

 name of Cupressus nootkatensis is to be regarded as the 

 authoritative one. 



Cupressus embraces five species which have been invariably 

 referred to it, C. macrocarpa, C. Goveniana, C. Macnabiana, C. 

 guadalupensis, and C. arizonica. Cupressus Lawsoniana of 

 Murray has been referred to the same genus by both Gordon 

 and Kellogg, but it has been assigned to Chamaecyparis by 

 Parlatore, Carriere, and Torrey. By the Index Kewensis Mur- 

 ray's name of Cupressus Lawsoniana is regarded as the one 

 which holds the greatest claim to recognition. It thus appears 

 that, although recent writers, such as Sargent, have recognized 

 Chamaecyparis as a distinct genus, the tendency has been to 

 divide it up among Thuya and Cupressus. It thus becomes 

 obvious that evidence derived from anatomical data which may 

 tend to throw its weight in favor of one or the other of these 

 views will be of special value. 



An examination of the characters already detailed for the 

 genera under consideration will show that the essential distinc- 

 tion rests upon the shape of the ray cells in tangential section 

 and upon the character of the terminal walls of the ray cells. 

 Thus in Thuya the ray cells are distinctly oblong, often quite 



