88 Proceedings of the Royal Irish Academy. 



epidermis. Another suggestion is tliat idioblasts are protective, reudering the 

 leaf unpalatable to weevils, beetles, etc. 



0. Resin-Canals. Two marginal resin-canals are present in the leaf iii all 

 the species, the onlv difference noted being that they are surrounded with 

 one layer of lining cells in P. japonica and P. sinensis, and with two layers in 

 the other species. 



6. McsophyU. In the two Chinese species the cell-walls of the spongy 

 mesophyll are infolded. This is not observable in the other species. 



7. Median Groove. The groove on the upper surface of the leaf in the 

 middle line is well marked, and continuous from base to apex in P. l)ontjlasii, 

 P.jajtonica, P. sinensis, and /'. Forrestii. It is slight and not continuous to 

 the apex in P. glauca and /'. macrocarpa. 



v.— The Oil Distilled raoM tiik Leaves. 



The diflference in the odour of the foliage of the Oregon and Colorado 

 Douglas Firs is remarkable and distinctive of the two trees.' The fragrance 

 of the Oregon species is agreeable, with a scent like pine-apples. The Colorado 

 species has a strong smell like tui^ntine. The odour is perceived near large 

 trees and in plantations in certain states of the atmosphere, and can always 

 be recognized by rubbing the fresh leaves between the fingers, or by placing 

 a branch of foliage in a vessel of water indoors, when the room soon becomes 

 tilled with the characteristic perfume. 



The h-aves of coniferous trees in general yield on distillation peculiar oils, 

 which are often of commercial value. The characteristic odour of each species 

 is doubtless due to the nature of the oil in the leaf. In order to test this, 

 quantities of the foliage of the two Douglas Firs were sent to Mr. C. T. 

 Bennett, B.sc., F.I.C., who has kindly supplietl the following details of analysis 

 of the oils distilled in the laboratorj- of Messrs. Wright, I>ayman,& Umney, 

 Ltd., Southwark, London, SJE.: — 



" Oregon Douglas Fir. 



" 1. 5') lbs. of leaves of young trees growing at Avondale, sent 

 in August. When distilled, less than 0*01 per cent, of an oil with 

 a very aromatic odour was obtained — a quantity too small for ex- 

 amination. 



' Attentinn w»s first drawn to the distinctive odours of the two DougIa.s Firs by 

 Mr. V. C. Le Fanu, of BAllyiDorris, Brav. Dr. Jncobi wrote in MUl. Drultch. Dcndr. 

 Get., 1914, p. 2'^4, «n the fragrance of the Oregon species as affected by the different 

 ttatea of the atmosphere. 



