1 86 BIOLOGICAL LECTURES. 



of these genera and finds its affinity with Sequoia and Taxo- 

 dium. A critical comparison of the remaining generic characters 

 will permit of more exact deductions as to the precise relations 

 in which these genera stand to one another. 



LlBOCEDRUS. 



Transverse. Summer wood, thin, rather dense ; the growth rings 

 usually showing a median layer of more dense structure. 



Radial. The terminal walls of the ray cells straight or somewhat 

 curved, entire, locally thickened, or even coarsely pitted; the pits on 

 the lateral walls of the ray cells small and simple. Pits on the 

 tangential walls of the summer tracheids very large and numerous. 



JUNIPERUS. 

 Transverse. Summer wood thin but very dense. 



Radial. Terminal walls of the ray cells thin and entire, more 

 rarely somewhat pitted; the pits on the lateral walls of the ray cells 

 often with a more or less obvious border. Pits on the tangential 

 walls of the summer tracheids chiefly small and not very numerous. 



THUYA. 

 Transverse. Summer wood thin, the structure rather dense. 



Radial. The terminal walls of the ray cells thin and not pitted 

 or locally thickened, usually much curved. Pits on the tangential 

 walls of the summer tracheids small to medium. 



Tangential. Ordinary rays narrow, the cells oblong, often very 

 narrow, more rarely oval. 



CUPRESSUS. 



Transverse. Summer wood very thin, often barely distinguishable ; 

 the structure open throughout. 



Radial. Terminal walls of the ray cells commonly curved, thin 

 and entire, or often locally thickened. Pits on the tangential walls 

 of the summer tracheids medium to large. 



Tangential. Ray cells chiefly broad, oval, or even transversely 

 oval, the rays often more or less two-seriate. 



