[PBNHALLOw] N. AMERICAN TAXACEyE AND CONIFERS 43 



The two genera, Thuya and Cupressus, arc very closely connected, 

 and for a long time morphologists have been unable to agree as to their 

 precise limitations. The Thuya occidentalis of Linnanis and T. gigantea 

 of Nuttall, appear to have been referred to this genus without exception. 

 Cupressus thyoides, of .Linna-us, was referred by Spach to Chamœcyparis 

 sphœroidea, by Sprengel to Thuya splueroidea and by Eichard to T. 

 sphœroidalis, a name which has been adopted by the Index Kewensis as 

 authoritative. Cupressus nutkœnsis of Hooker or C. nootkatensis of 

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

 species C. americana. By Carrière it was referred to the genus Thuyopsis 

 and at different times to T. borealis and T. cupressoides. Both iSpach and 

 Walpers referred it to the genus Chamœcyparis, and Fischer also recog- 

 nized the same genus but applied the specific name of C. exctlsa. 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. Cujjressus Lawsoniana of Murray has been referi-ed to the 

 same genus by both Gordon and Kellogg, but it has been assigned to 

 Chamœcyparis b}^ Parlatore, Carrière and Torrey. By the Index 

 Kewensis, Murray'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 Chamœcyparis 

 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 favour of one or 

 the other of these views, will be of special value. 



An examination of the characters already detailed for the genera 

 under considei'ation will show that the essential distinction rests upon the 

 shape of the ray-cells ni 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 narrow, more rarely oval, while the terminal 

 walls of the raj^-cells are conspicuously devoid of pits or local thicken- 

 ings. In Cupressus, on the other hand, the rays are distinctly broader, 

 the cells are oval, or even transversely oval, rarely oblong. The walls 

 are also much thicker as a rule. The terminal walls of the ray-cells are 

 thin and often entire, but they also frequently show very obvious local 

 thickenings. These characters are well defined, and, so far as a large 

 amount of material will j^ermit a definite conclusion, constant. These 

 characters, therefore, may safely be taken as marking the limitations of 

 the genera. On this basis, Chamœcyparis nutkœnsis of Spach must be 

 restored to the genus Cupressus under Lambert's name of C. nootkatensis. 

 The genus dhamœcyparis thus disappears altogether, a change which is 



