[pEKHALLow] N. AMERICAN TAXACE^E AND CONIFERS 4S 



genus. Both of these genera approach Junijjeras in the presence of pro- 

 minent resin-cells, as well as in the fact that these elements are disposed 

 in tangential bands. To this must also be added the fact, already pointed 

 out, that a further affinity is based upon the occurrence in all three of 

 bordei'ed pits on the lateral walls of the ray-cells, and similarity of struc- 

 ture in the terminal walls of the ray-cells. The occurrence of occasional 

 resin-passages in Sequoia semperviî'ens, and a similar occurrence of imper- 

 fectly formed resin-passages in Abies nobilis. point to the fact that there 

 is a strong point of contact between these two genera. 



The relation between Sequoia and Abies thus indicated is greatly 

 strengthened in other wa3's, as in the absence of resin-passages and fusi- 

 form rays, together with the occurrence of i.solated resin-celLs. Abies^ on 

 the other hand, approaches the genus Tsuya, not only in a closer general 

 resemblance of the structure as displayed in transverse section, but in the 

 peculiar distribution of the resin-cells on the outer face of the summer 

 wood, a character which is likewise common to Fseudotsucja and Larix, 

 In this last character a certain affinity with Picea is indicated, since in 

 the latter the resin-cells are wholly wanting, while in Abies they have so 

 far disappeared as to be very scattering and olten rather obscure. Never- 

 theless the weight of evidence shows that there is no direct relation with 

 Ficea, more especially when to the facts already stated we add those 

 elements to be derived from the structure of the ray. In Sequoia and 

 Taxodiuvi there are no ray-tracheids. In Tsuga, on the other hand the 

 tracheids constitute a very promment feature in the composition of the 

 medullary rays. In Abies, all the North American species, with the single 

 exception of .1. balsamea, as long since pointed out by JDeBary,' are 

 devoid of tracheids, and in this single species these structures are to be 

 found but sparingly. The systematic position of this genus in relation 

 to Sequoia on the one hand, and to Tsuya on the other, is thus a matter 

 of well defined certainty. 



The three genera, Tsuga, Fseudotsuga and Zarix, po.ssess the com- 

 mon characteristic of having their resin-cells scattering on the outer face 

 of the summer wood. They are also joined by the presence of ray- 

 tracheids. Tsuga nevertheless stands apart, and tinds alliance with Abies, 

 Sequoia and others of that group, through the absence of resin-passages 

 and fusiform rays, elements which are not only prominent in Fseudotsuga 

 and Larix, but also in Ficea and Finus. Fseudotsuga, Lanx and Ficea 

 are yet more closely related by reason of the great similarity of the fusi- 

 form rays. These structures, within the limits of this group, are gener- 

 ally distinguished by the rather abrupt contraction of the central tract 

 into linear terminals, which often become much prolonged. The cells 

 are thick-walled, and the resin-passage is chiefly devoid of thyloses, while 



Com. Anat., 1884, p. 490. 



