Oak Mildeiv on Beech in Britain. A. D. Cotton. 199 



by Mr. E. S. Salmon, the author of the monograph of the 

 Erysiphaceae. Some difference of opinion, however, exists as 

 to whether the fungus should be regarded as species, variety, 

 or biologic form, and a number of papers bearing on this subject, 

 especially in French journals, have been published. Griffon 

 and Maublanc regard it as a distinct species and have published 

 the name Microsphacra alpJiitoides. 



The method of over-wintering of the Oak Mildew fungus is 

 the same as that which occurs in the fungi causing Apple 

 Mildew and Hawthorn Mildew, namely by the hibernation of 

 mycelium. The latter penetrates the buds in autumn, remains 

 dormant during winter, and develops again in spring with the 

 unfolding of the leaves. It would seem that only a very few 

 buds are infected in this way but it is obvious that a sufficient 

 number occur to provide a copious supply of conidiospores and 

 general infection each season. The production of perithecia 

 is therefore not required. 



A considerable amount of work on the biology of the fungus 

 has been carried out on the Continent and one of the fullest 

 accounts of such work is that by Neger (Naturwiss. Zeitschrift. 

 fiir Land- und Forstwirtschaft. xiii). With regard to its 

 occurrence on Beech, several workers have recorded this 

 phenomenon, e.g. Griffon and Maublanc 1908, Ferraris 1909, 

 Forneti 1910, Miiller 1911, Hauck and Kolpin Ravn 1913, 

 and' Neger 19 15, but apparently the last-named alone clinched 

 the matter by means of artificial cultures. The occurrence 

 of the mildew on Beech is therefore not new but a record of 

 its occasional appearance in this country is none the less of 

 interest. 



The mildew was observed on this host by the writer near 

 Sevenoaks, Kent, on several occasions in July 1918. It 

 occurred on shoots springing from the stumps of old trees which 

 had been cut down and in some instances it was quite clear that 

 the Beech was being infected directly from spores produced 

 on the Oak. In one case some half-dozen stumps in the imme- 

 diate neighbourhood of badly mildewed oak shoots possessed 

 young shoots most of which were more or less mildewed, whilst 

 the shoots of other stumps not in close proximity to mildewed 

 oak were clean. Closer inspection showed that young beech 

 shoots growing immediately under infected oak were developing 

 a slight growth of mildew, whereas the other shoots of the same 

 age not beneath the oak shoots were free from attack. The 

 ^affected shoots were so close to the oak that a copious supply 

 of spores must have fallen upon them, and the young leaves 

 must have received a constant new supply of spores during the 

 whole period of their development. When infected directly from 



