336 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



only locally thickened, but in such cases the typical feature 

 always appears in the summer wood where such secondary alter- 

 ations are most strongly emphasized. 



For taxonomic purposes, such features possess a definite 



value. The thick-walled cells of Tsuga, Larix and Picea permit 

 ' of an easy and definite segregation of these three genera in those 

 cases which otherwise might involve a strong element of doubt, 

 and the same rule holds true, though to a less extent, with 



respect to the locally thickened walls in Cupressus and related 

 genera. 



Pits on the lateral walls of the ray cells are an invariable 

 feature of all investigated species of Ginkgoales and Coniferales, 

 including fossil representatives and the Cordaitales. They vary 

 very much in form, size and number. In such types as Juni- 

 perus, they are most diminutive (Fig. 21) and generally numer- 

 ous, while in many of the pines, such as P. resinosa, P. kora- 

 iensis or P. reflexa (Fig. 22) they attain to maximum size and 



