OBSEEYATIONS ON CANADIAN CONIFERS. 33 



Botanically there is only one species of Douglas fir (Pseudots)iga drmglasii), but of this 

 there is also a varietal form (P. douglasii var. macrocarpa), whicli (lifi:ers from the specific 

 type in several respects. According to the descriptions of Prof C. S. Sargent,' these woods 

 answer to the following characteristics : 



" PSETJDOTSUGA DOUGLASII. 



" Wood hard, strong, varying greatly with age and conditions of growth in density, 

 quality and amount of sap ; difiicnlt to work, durable ; the bands of small summer cells 

 dark-coloured, conspicuous, soon becoming flinty and difficult to cut ; colour varying from 

 light red to yellow ; specific gravity 0-5157, ash 0-08. Two varieties, red and yellow fir, are 

 distinguished by lumbermen, dependent probably upon the age of the tree ; the former 

 coarse-grained, darker coloured, and considered less valual)le than yellow fir." 



"PSEUDOTSUGA DOUGLASII Var. MACROCARPA. 



"Wood heavy, hard, strong, cross-grained, very durable, difficult to work; coluui- rather 

 darker red than that of the species ; specific gravity 0'4563, ash 0-08." 



The specimens now under discussion are all of the " yellow " variety, though, as will 

 appear more conspicuously later, l)oth the "fine-grained" and the "coarse-grained" forms 

 are represented. While these designations may be employed, they do not represent the 

 most reliable means of ascertaining tlie value of the wood for structural purposes, although 

 to the experienced lumberman they may be all that is required for an accurate designation. 



Growth-rings. 



The growth-rings in Pseudotsuga are extremely variable, so much so, in fact, that when 

 certain cross-sections, taken from different trees, are brought into comparison, either macro- 

 scopically or microscopically, it would be extremel}' difficult to recognize their relationship 

 to one another. It may also be added that no other species of conifer, so far as I am aware, 

 exhibits the same degree or kind of variation. These deviations relate to the thickness of 

 the growth-rings, and to the relative volume and general character of the summer wood. 



Upon examining a large cross-section of this timber, one of the most striking facts 

 appears in the zonal disposition of the growth-rings. These zones vary much in width, and 

 while the component rings of contiguous zones show well-marked differences in size, within 

 each zone the range of variation is narrow, and oftentimes the rings present remarkable 

 uniformity. So well marked are these differences that when a number of trees have been 

 examined, it is possible to establish an exact correspondence of zones hj means of the aver- 

 age dimension of the component growth-rings. Within the limits of the five specimens now 

 under consideration, I have carefully examined, measured and tabulated a total of five hun- 

 dred and sixty-four growth-rings. In establishing these zones the limits were determined 

 wherever a marked and permanent change in size occurred. Thus, the values 4*25, 4-25, 

 4-25, 3-25, 3-00, 3-00, 3-50, etc., would show that the bounding-line must lie in this case 

 between 4-25 and 3'25. In this way it has been possible to recognize four well-marked 

 zones, and doubtless a complete transverse section of a tree of large diameter would show a 

 higher number than this. Commencing with the centre of the tree, tlie rings of zone 1 



' " Tenth Census United States, Forestry," ix., 209. 



Sec. III., 1894. 5 



