82 Proceedings of the Royal Irish Academy. 



9. Insect Attack. During the last six years a species of Cbermes, identified 

 by the Bureau of Entomology, U. S. Department of Agriculture, with 

 Ghermes coohyi, Gillette, var. Coircni, lias been noticed in the south of 

 England on the Oregon Douglas Vir.' It has been observed mainly on the 

 lower and partially shaded branches of fairly large trees, and so far has 

 done little harm. It has not yet been found in England on the Colorado 

 species. This is remnrkable, as in the contiguous plantations of the two 

 species in Bagley Wood, Oxford, and at Highfield, East Liss, the insect does 

 not spread from the trees of the Oregon species on which it occurs to those 

 immediately adjoining of the other species. 



This Chermes, however, occurs in the forests of Pseudotsuga (jlmica in the 

 Rocky Mountains, and on ornamental trees of this species on the Atlantic 

 coast. It was recorded from only park trees in the Pacific coast region ; 

 but Dr. E. J. I'erkins last year collected branches of Douglas Fir in a wild 

 forest in Oregon which were badly infested with a Chermes indistinguishable 

 from C. Coolei/i. The gall form of the insect is common on Sitka Spruce in 

 Oregon, Washington, and British Columbia, and on Picen pioiffcns and 

 /'. Kinielmnnni in tlie I{ix;ky Mountains. 



10. Unte of Grmoth. The two Douglas Firs difl'er remarkably in their rate 

 of growth. The Colorado species at all ages is much less in height and 

 diameter. It attains on an average about half the height of the Oregon 

 species, l>oth in America and in cultivation in this country. I'lie following 

 figures for forest trees on good soil in the United States illustrate this : — 

 P. glaiifti, in the Rocky Mountains, eastern Idaho, .54 feet high, at seventy 

 yeai-8 old ; P. Douffhsii, in western Wa.shington, 106 feet in height, at the 

 same age. The dianiet^-rs of the trees in Idaho at fifty, sixty, and .seventy 

 years old are lialf those in Washington at the same ages. Young plantations 

 in England are similar in their developinent, as will be seen from the 

 measurements given l>elow. 



11. Vol Hint find Yi'ld of Timber. As may readily be deduced from the 

 comparative rales of growth in height and diameter, the volume of timber 

 produced by the two species is extraordinarily diflerent in amount. 'The 

 Pacific coast tree exceeds in yield of timber per acre four to ten-fold the 

 Colorado Douglas Fir. This will be illustrated in the following account of the 

 behaviour of the two species under cultivation in plantations in this country. 



12. SUvicuUiirc. The Colorado Douglas Fir has been tried as a forest 

 tree in several places in Great Britain, but has invariably proved a failure. 



' It WHS tint seen by Mr. A. C. Forbes and Professor A. Henry on trees in tlie New 

 Forest in .Tvily, lt»13. It has since been observed near Kast Grinstend (Sussex), 

 Petersfield and East Lias (Hants), Buckhold (Berks), and Bagley Wood (Oxon). 



