NEW DISEASE OF DOUGLAS FIR IN SCOTLAND. 1 47 



the fungus found on the Douglas fir in Scotland. The descrip- 

 tion of the fungus is as follows J : — 



Phomopsis Pseudotsugae, n.sp. 



Pycnidia lens shaped to conical, depressed and with a broader 

 base, "3-1 mm. broad, -2--^ mm. high, at first covered with the 

 bark or leaf epidermis, later breaking through (in the case of 

 the bark by an elongated slit) and projecting slightly, solitary 

 or in groups of two, scattered, dull black and slightly roughened ; 

 texture everywhere several cells thick, more or less hyaline and 

 tinged with green below, thicker and black above, opening with 

 a definite ostiole ; internal cavity partially divided up into 

 several chambers by partitions greenish in colour and springing 

 from the inner wall ; spores hyaline, of two kinds — A-spores, 

 elliptical- fusoid, obtuse at both ends, 5 '5-8-5 x 2*5-4/x, without 

 oil drops but with a minute granule towards one or both ends, 

 with subulate sporophores about 13/z long; B-spores, rod-like 

 generally curved, obtuse at each end without oil drops, 

 5-6 x i*5/x with subulate sporophores 12-14 x 1-2/*. 



The spores are shown in Figs. 6 (A-spores) and 7 (B-spores). 

 The pycnidia containing A-spores are generally rather larger, 

 often in groups of two, and have been found on the older parts of 

 the host-plant, never on the leaves ; only A-spores have been 

 found on plants attacked near ground-level. Pycnidia containing 

 B-sporesare usuallyrathersmaller, moredecidedly conical, solitary, 

 and have been found on both surfaces of the leaves, usually on 

 the upper surface, and on the younger parts of the one-year old 

 stems. Both kinds of spores emerge from the pycnidia in similar 

 ways (Fig. 4). The sporophores usually remain inside the pycni- 

 dium attached to the walls and forming a distinct zone (Fig. 5, a). 

 They are quite distinct in the young pycnidium, and can be seen 

 attached to the spores (Figs. 6 and 7), but in the older pycnidia 

 they appear to become mucilaginous and partially disintegrate. 



A plantation of Douglas fir in Perthshire, about 6-8 years old, 

 was examined in April of this year, and it was estimated that 

 half of the trees had been killed by the disease. The dead trees 

 were removed and burnt and the spaces were filled up by 

 planting fresh trees. In September about 20 % of the trees were 

 showing signs of attack, and these included some of those 

 planted in the previous April. 



1 See also Trans. Bot. Soc, Edin., vol. xxviii., pt. 1 (1920). 



