No. 449-] NORTH AMERICAN CONIFERALES. 335 



features which are usually of very secondary value, although in 

 a few cases, as Taxodium, it may serve a useful purpose as 

 an associated character, for differentiation from closely allied 

 genera (Fig, 18). In other cases the wall is more or less 

 strongly curved. This feature is prominent in Thuya, Cupres- 

 sus, Podocarpus, Thujopsis and Cryptomeria, as also in the more 

 highly developed hard pines. To a less extent it also occurs in 

 Taxodium, and it constitutes a character of some value for differ- 

 ential purposes (Fig. 19). 



The second variant differs from the first in that the otherwise 

 thin wall is locally thickened (Fig. 20), the secondary growth 

 forming one or more beaded enlargements. This is a feature 

 which occurs exceptionally in Abies, Pseudotsuga. I'it ca and 

 Pinus, but it is typical in Cupressus (66.0 %) and juni])crus 



(72.7 %) where it 



t of great valut 



tes a diagnostic elem 

 It is in all cases, however, to be regarded as a transii 

 between the first and the third variants, and from th 

 view it also possesses a somewhat definite ph>l<)gci 

 The third variant is characterized by a marked gencr 

 ary growth of the wall, which thereby becomes m.M c ... .w. 

 strongly thickened and traversed by numerous simple pits 

 (Fig. 21). It occurs exceptionally in Juniperus and Pmus, but 

 it is typical in Abies (90.9 % ), Tsuga ( 1 00.0 1r ), Larix ( 1 00.0 7^ ) 

 and Picea (90.0 %). In Abies and Juniperus, where transitional 

 forms sometimes occur, the walls in the spring wood may be 



