1919-20.] BOTANICAL SOCIETY OB' EDINBURGH 47 



A New Species of Phomopsis Parasitic on the 

 Douglas Fir. By Malcolm Wilson, D.Sc, F.R.S.E., 

 F.L.S. 



(Read 10th June and 21st October 1920.) 



Phomopsis Pseudotsugae, n. sp. 



Pycnidia undique densiuscule distributa vulgo 2-3 mm. 

 inter se distantia, obpyriformia, basi complanata, e cortice 

 rupta paullo protrusa, opaco-iiigrida, 'S-l mm. diametro, 

 ostiolo pertusa, intus plurilocellaria disseptis centralibus 

 tenuibus atque cum muris obscure nigro-olivaceis ; sporulae 

 hyalinae, dimorphae ; aliae (A-sporulae) elliptico-fusoideae, 

 eguttulatae, utrinque obtusae 5'5-8'5 x 2"5-4/Lt, sporo- 

 phoris subulatis circiter IS /u longis; aliae (B-sporulae) in 

 pycnidiis discretis orientes, bacillares, curvatae vel raro 

 rectae, eguttulatae, utrinque obtusae, 5-6x1 5 /ul, sporo- 

 phoris rectis, subulatis, 13 x 1-2 ju. 



Hab. in ramis foliisque vivis Pseudotsugae Douglasii 

 quam in Scotia multo vexat. 



The fungus attacks the Douglas fir ^ in two distinct 

 ways. In the first the leading shoot is killed back for a 

 variable distance, usually about 9 inches. In the second the 

 young tree is attacked a short distance above the ground 

 level ; the outer tissues are killed either on one side only 

 or completely round the stem, and ultimately the w^hole 

 tree is killed. In both cases a very characteristic feature 

 of the disease is the sudden decrease in diameter in passing 

 from the healthy to the diseased portion of the stem. The 

 fungus has been found up to the present only on trees up 

 to twelve years old. 



The pycnidia are at first covered by the bark or epidermis 

 of the leaf, and later on break through, in the case of those 

 on the stems, by means of an elongated slit. Those con- 

 taining A-spores are generally rather larger, are often 

 found in groups of two, and occur on the older parts of 

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

 found on plants attacked near ground level. Pycnidia 

 containing B-spores are usually rather smaller, more 



^ An account of the effect of the fungus on its host appears in the 

 current number of the Transactions of the Royal Scottish Arboricultural 

 Society. 



