546 THE AMERICAN NATURALIST. [Vol. XXXVIII. 



longitudinal section the reservoirs are variously rounded or 

 oblong cysts, contiguous or isolated, and forming a longitudinal 

 series. In their general form and structure they are essentially 

 the same as in Sequoia. 



In the genus Abies secretory reservoirs occur in at least four 

 species where they form more or less extensive tangential series, 

 within which they are usually contiguous and more or less con- 

 fluent. They present the same general variations in structural 

 organization as in Tsuga and Sequoia, but in A. concolor, and 

 less conspicuously in A. nobilis, they are often extended in a 

 radial direction so as to become narrowly oval or oblong, and 

 several times longer than broad. The epithelium consists of a 

 well defined structure composed of one to three rows of cells. 

 The first row, immediately bordering upon the canal, consists of 

 rounded or oval and thick-walled cells which are much smaller 

 than those of Sequoia, and similar to those of Tsuga. They are 

 always characterized by an abundance of strongly defined, simple 

 pits, and many of them contain resin, which usually takes the 

 form of rounded granules of diverse sizes. The parenchyma 

 tracheids are so nearly like the accompanying wood tracheids as, 

 in some cases, to be separable with some difficulty, but they 

 generally surround the resin sac, at least within the limits of the 

 spring wood, and they not infrequently replace the parenchyma 

 cells of the epithelium more or less completely. Not infre- 

 quently they form somewhat extended radial series from the 

 epithelium into the spring wood, as in Picea (Fig. 48). In such 

 cases they are usually recognizable by their rather unusual size 

 and thinner walls, and in addition they commonly show bordered 

 pits on the tangential walls. When the terminal wall lies suffi- 

 ciently near to the plane of section, it shows from one to several 

 rather large bordered pits, and by this feature such tracheids 

 may be located with much certainty. Thyloses have been defi- 

 nitely noted only in the case of A. concolor, in which species 

 they are essentially of the same general character as in Sequoia, 

 They are thick-walled and either isolated or so numerous as to 

 re cyst. In one case of contiguous cysts, an epithe- 

 i found to form thyloses in both cysts — in the one 

 I isolated cell, in the other forming a tissue 



fill the ( 



which nearly filled the entire ( 



vity. 



