72 Prnceerlwgs of the Roi/al Irish A cademy. 



cultivatiou in Europe ; but it grows iu Washington and Oregon, on the 

 edges of ocean inlets, where the least rise submerges its roots. 



• In Washington and Oregon it bears less shade than Sitka Spruce, Western 

 Hemlock, Tlnuja gigantca, and Abies grandis; but maintains itself in 

 competitiun with these species on account of its greater rate of height growth, 

 and it« adaptability to varying conditions of soil and moisture. It demands 

 for its best growth an abundance of liglit overhead, but produces the tallest 

 and straightest stems when well shaded from the side. It attains its optimum 

 develoi'iuent in cvt-n-aged stands, where all the trees are about tlie same 

 height, and all receive direct top-light. '.!rown in this way, the stems are 

 cylindrical in form and crowded upon the ground, yielding an immense 

 volume of timber )ier acre. The branches are very persistent, and remain on 

 the stem long after their foliage has died from lack of light. Even in dense 

 stands on the I'acific coast, the shedding of ihe dead branches only begins 

 when the trees are forty years old ; and stems clear and smooth below the 

 crown of living foliage are not produced till seventy or eighty yeare old. 



Owing to the remarkable rate of its growth in height and diameter, and 

 its capacity to form dense stands, the Oregon iJouglas Fir excels in North 

 America all other species in tlie yield of timber per acre. The yield tables,^ 

 compiled from measurements taken by Han/.lik in 568 plots in the forests of 

 this 8i)ecies in Oregon and Wa.shingti»n, show that between tha ages of 50 

 and 120 yeara the mean annual increment in volume is about 170 cubic feet 

 per acre on first-class sites, 130 cubic feet on second-class sites, and 100 cubic 

 feet on infeiior sites. Mucli higher yields would be reckoned if thinnings 

 could have been included ; but account was only taken of the timber actually 

 growing on the ground at the tune of measurement. These tables show 

 that on gooil soil an acre of Oregon l>ougla8 Fir at sixty years old measures 

 10,000 cubic feet of timber, the average height of the trees being 120 feet. 

 Mungei"' gives the average heitfht on good soil in the forests of Washington as 

 110 to 130 feet at seventy years old, and 150 to 190 feet at 150 years old. 



Pseudotsoga Douglasii var. caesia. 



This variety, whicli was described by Schwerin in Mill. Deulsch. Dendr. 

 Gcs., 1907, p. 257, attains a height of 100 to 150 feet. Lranchlets glabrous, 

 grey iu the hrat winter and second and third yeai-s ; pulvini slightly 

 prominent ; buds resinous. Leaves pectinate, with a trace of glaucous 

 bloom, resembling the type in the continuous median groove above, but 

 intermediate in most resijects between the Oregon and Colorado species. A 



• (/iiarierhj Journal of Foralrij, viii, HO (1914). 



' U. S. Dtpt. Agrie. Fvrul <)irc<dar. No. 175 (1911). 



