68 Proceedings of the Royal Irish Academii. 



has been very scanty, while cultivated specimens are exti'emely rare, con- 

 sisting of a few small plants of two or three species, only recently introduced. 

 A brief reference may now be made to some other results of the present 

 investigation, of which further details will be given in the succeeding pages. 

 The microscopic structure of the leaves has been found to be a distinct and 

 constant character in eacli species, evidently l)eing correlated with the special 

 climate in which the tree lives in a wild state. The Colorado and Oregon 

 Douglas Firs exemplify this in a striking manner, the leaf-anatomy of the 

 former showing many xerophytic features which are adaptations to the dry 

 and continental climate of the liocky Mountains. The notable diflerence in 

 the odour exhaled by these two trees led to an examination of the oil which 

 is obtained by distillation from their foliage. This oil proves in each species 

 to be very distinct in chemical composition. A similar diflerence exists in 

 the oil of the various forms of the Yellow Pine, which occur in the same 

 territory as the American Douglas Firs. 



II.— TiiK Gksis Tseudotsuga. 



Pseudotsuga is a genus of Abietineae, akin to Larix in the structure and 

 qualities of the wood and in its embryonic history,' but resembling Abies in the 

 solitary evergreen needles. Main branches whorled. Bark on young stems, 

 smooth and witli resin-vcsiclcs ; on older trunks, lliick, corky, furrowed, con- 

 sisting of aliernale thin wliite layers and tliick reddish-brown layers. 

 Branchlels with somewhat raised pulviui, each coloured around tlie projecting 

 apex, which bears a single leaf, liuds diagnostic of the genus, spindle- 

 shaped, sharp-pointed, with numerous sliining brown scales. leaves linear, 

 narrowed at the base, with a median furrow above, and a green midrib and 

 two stomatic bands beneath ; transverse section with a single fibro-vascular 

 bundle and two marginal resin-canals. 



Cones short-stalked, pendulous, ripening in the first season, the rounded 

 scales gaping to let out the rii»e seed ; bracts conspicuous, exserted, three- 

 lobed at the apex, the terminal lobe awu-like. Seed without resin-vesicles, 

 differing fj-om that of Lanx in tiie pointed base ; wing large, rounded above, 

 not detachable without breaking, covering not only tiie upper surface, but 

 also a considerable part of the lower surface of the seed. 



Seven specimens of I'seudotsuga have been described, three occurring in 

 western North America, and four restricted to small areas in western China, 

 Formosa, and Japan. These may be arranged as follows : — 



' See Jcseph Doyle, in Scient. Proc. R. Dublin Stx. iv, 325 (1918), on the various 

 points t>f agrcvmcut, which establish a close natural affinity between Litrix and 

 pseudotsuga. 



