II. CONIFERS 



(Note. The following applies to those woods only, which are prescribed 

 for the course in Forestry at Cambridge.) 



All the coniferous woods that concern us at present, exhibit a pro- 

 nounced difference in density between the inner and outer zones of the 

 same annual ring, hence in transverse section the rings are sharply 

 marked off and in longitudinal section (on the plank-face) the wood is 

 definitely and sometimes boldly striped. In many of the Cupressinea*, 

 the distinction of the zones of the ring is reduced to a line of denser 

 tissue at the extreme boundary of the ring or may be altogether wanting 

 as in some species of Podocarpus. 



Woods either without pores of any kind or, if pores be present (in the 

 form of resin-canals), they are never in the inner (Spring) zone of the 

 annual ring (compare Figs. 1-3). The resin-canals are often present in 

 the middle of the ring where the tissue is still soft, lax and light-coloured. 

 In comparison with the vessels of the Broad-leaved trees, they are 

 exceedingly few in numbers, often far apart and rarely, if ever, in more 

 than one or at most two, very imperfect rows. These rows are interrupted 

 in the most irregular manner, sometimes inches of arc being without them. 

 They never exceed 50 to the inch of arc in any ring, whereas in the wood 

 of the Broad-leaved trees the vessels are never less than a hundred 

 (generally many hundreds), in that distance. The resin-canals may appear 

 on a transverse section as white points, sometimes visible to the unaided 

 eye, but always with ease with the lens unless their colour renders them 

 obscure, that is to say, they are never so very small as are sometimes 

 the vessels of the Broad-leaved trees. The species included in the course, 

 that have such vertical resin-canals are : Pinus sylvestris, the Scots Fir ; 

 Pinus Strobus, the White Pine of America known as the Weymouth Pine 

 in England ; Pinus palustris, the American Pitch Pine of export ; Picea 

 excelsa, the Common Spruce; Larix europcea, the Larch; and Pseudo- 

 Tsuga Douglasii, the Douglas Fir. 



Inasmuch as horizontal resin-canals occur in the larger rays of all 

 our present species which present vertical resin-canals, the presence of 

 the one can be predicted from that of the other. This is important as 

 the vertical resin-canals of the Spruce are exceedingly rare at times, and 

 may be overlooked whereas in the Silver Fir (a species generally confused 

 with the Spruce), there are no resin-canals of any kind. The species 

 of Conifers lacking resin-canals are: Abies pectinata, the Silver Fir (< 

 after wounding) ; Taxus baccata, the Yew-tree ; Sequoia semperyirens, the 

 Giant Redwood (except after wounding) ; and Juniperus virginiana, the 

 Pencil Cedar. 



35 3-2 



