CONIFERS. 395 



cells tapering 1 at the ends ; in the case of most species these wood cells 

 are large and visible under the lens. The annual rings are, as a rule, 

 distinctly marked by a belt of thick-walled wood-cells in the outer 

 (autumn) wood and a belt of larger and thin-walled wood cells in the 

 inner (spring) wood. 



In the case of the Juniper, Cypress, Yew and Podocarpus, the 

 firmer belt of autumn wood is narrow, and the whole structure of the 

 wood, therefore, is homogeneous. On the other hand, in the case of 

 the Pines, Firs, Cedar and Larch the wood consists of alternate layers of 

 soft spring wood and firm autumn wood. 



The turpentine (resin) is secreted in large, branching, intercellular 

 ducts, lined by thin-walled cells. These cavities are called ' resinous 

 ducts/ and they are of two classes ; vertical, running with the wood-cells 

 parallel to the axis of the stem, and horizontal ducts, running" with the 

 medullary rays. The horizontal ducts can, as a rule, only be seen under 

 the microscope ; they will, therefore, not be generally noted in the follow- 

 ing descriptions. The vertical ducts appear on a cross section as scattered 

 pores varying in size. Resin is also found in parenchymatic cells with 

 straight ends, which are found mixed with ordinary wood cells : this is 

 the case in Cypress. 



The timber is homogeneous in the case of Cupressinese and Taxinese, 

 but, as explained, in the case of AbietineaB it consists of alternate layers 

 of soft spring wood and hard autumn wood. The value of the timber of 

 Abietinea3 for building purposes depends in a great measure upon the 

 greater or less proportion of the firmer belt of autumn wood and also 

 upon the more or less spongy nature of the spring wood. Under certain 

 circumstances, for instance, the timber of Deodar has an extremely soft 

 and spongy spring wood, and a comparatively narrow belt of autumn 

 wood. Such timber is probably less durable and not as strong as timber 

 grown under other circumstances, which has a less spongy spring wood 

 and a larger proportion of firm autumn wood. Similar variations in the 

 structure may be noticed in the case of Pinus longifolia and other conifer- 

 ous trees, and it is a subject worth careful enquiry how far durability 

 and strength are effected by these characters, and to determine the 

 conditions of growth under which the wood of coniferous trees exhibits 

 the varieties of structure here adverted to. It is generally supposed that 

 slow-grown timber of coniferous trees is heavier and more durable than, 

 timber of the same species which had grown more rapidly. This, how- 

 ever, is not always the case. The following are instances of a light 

 weight in the case of slow-grown timbers : 



Ibs. 



Pinus excelsa H 140. (22 rings) 26 



Cedrus Deodara H 902. (34 32 . 



Logs which contain much resin are heavier than those which contain 

 little resin. 



With few exceptions the woad of coniferous ti'ees seasons well. The 

 woods are light, the weight per cubic foot ranging between 20 and 

 40 Ibs., with few exceptions, such a.s Tu.xus, which weighs over -10 Ibs. 



1. PINUS, Linn. 

 Five Indian species; the whole genus according to Parlatore in DeCandolle's 



