PINACEiE 481 



Naturally a light- demanding tree, it appears to be most 

 satisfactory in this country when treated as a pure crop. Good 

 results have, however, been obtained by mixing it with Thuya 

 plicata. In America trees growing in dense forests are said to 

 clean their trunks well. That, however, is not the experience 

 of foresters in this country. Even when spaced 4 ft. apart each 

 way the inside trees in a plantation keep their lower branches 

 alive for many years, and after death they remain sound and do 

 not fall naturally. Lower branches therefore must be pruned, 

 and if pruning is necessary with close planting, it is just as well 

 to adopt wider spacing, 5-6 ft., and allow the young trees to 

 benefit by the extra light and air, thus saving the expense in 

 plants and planting that will be necessary for pruning. It is 

 probable that in the natural forests of W.N. America a very 

 dense crop following regeneration helps the trees to clean their 

 trunks. Young plants should not exceed 2 ft. in height at plant- 

 ing time. In America it is recommended that at 20 years of age 

 the trees should stand about 990 to the acre ; at 30 years of age 

 580 ; and at 100 years about 115 to the acre.^ It is probable 

 that P. Douglasii may be most satisfactorily grown in this 

 country on a 60-70 years' rotation. The Colorado Douglas Fir 

 (P. glaiica) grows at less than half the rate of the Oregon tree. 

 Young trees of the Oregon Douglas fir seed freely in Britain, 

 and self-sown seedlings are common in Hampshire and other 

 places. 



Both imported and home-grown seeds are often destroyed by 

 the larvae of an insect, Megastigmus spermotrophus. In order 

 to check this enemy, infested seed should be fumigated with 

 hydrocyanic gas. During the last few years the Oregon 

 Douglas fir has been infested in many parts of the country with 

 the Douglas Fir Chermes (Chermes cooleyi, Gillett),^ an insect 

 which passes part of its life-history on Douglas fir and part on 

 Sitka spruce. The insect, however, attacks the leaves only of 

 the Douglas fir, and probably will not cause serious harm. 



Pseudotsuga Forrestii, Craib.' 



Forrest's Douglas Fir. 



A tree 60-80 ft. high in W. China. Winter hucls slightly 

 resinous. Young shoots reddish brown at first, assuming a 

 greyish tinge with age, without down or with minute scattered 

 hairs. Leaves pectinate, up to nearly 2 in, long, notched at the 

 apex, upper surface furrowed from base to apex, lower surface 

 with two narrow white bands of minute stomata. Cones about 



^ For. Ser. Circ. U.S.A., 175, Growth and Management of Douglas Fir (1911). 



^For. Gomm. Bull. (London), No. 4 (11)22). 



^ Notes Roy. Bot. Qard. Edinburgh, xi, 189, t. IGO (1919). 



1 I 



