348 



THE AMERICAN NATURALIST. [Vol. XXXVIII. 



cells are thick and traversed by small pits. In the 

 genus Pinus the wall is commonly thin and it closes 

 (0)1 the orifice of a very large pit on the wall of the 

 adjacent wood tracheid. This is notably true of 

 '/qI the soft pines in which the side wall either projects 

 as a convex membrane, or it is concave and curves 

 into the cell cavity. Such a feature is of very little 

 if any importance with the exception P. rejlexa, in 

 which the thin side walls almost invariably project 

 so as to give the cells a correspondingly inflated 

 appearance (Fig. 2'ja). It is not only apparent in 

 a tangential section, but it is very conspicuous in 

 the transverse section (Fig. 2^6) where the inflated 

 walls are seen to project into the cavities of adja- 

 cent wood tracheids, thereby giving to the ray a 

 beaded appearance. As an exceptional variation it 

 possesses no apparent significance with respect to 

 questions of descent. 



The second form of the ray is that which has 

 been designated as fusiform in reference to its 

 characteristic outline (39). Such rays occur in 

 relatively few of the existing genera to the extent 

 of 20 f. They occur typically in Fseudotsuga, 

 Larix, Picea and Pinus, and they are thus seen to 

 be characteristic of the most advanced types. 

 Among extinct species they are unknown except 

 in the case of Sequoia burgessii^ (41, 42-46) 

 which they present a remarkable exception to the 

 general course of development and structure of 

 that genus. The fusiform rays are peculiar in 

 %.-Pseudot. their structural features. They vary greatly in 

 genSf^T^- ^^ight as between different genera, and such vari- 

 of a fusiform atlous also occur within a given genus, the ex- 

 typicai resfn trcmcs bciug mct with in the genus Pinus, where 

 ^7''epUheH-" P-pahistris and P.ponderosa present the antithetic 

 but devoid relations. In most cases they are much higher 

 ^ ^ than the uniseriate rays with which they are asso- 



ir. E. C. Jeffrey has recently discovered the same feature in another extinct 

 oia now in course of publication. 



