200 ON THE PEKONOSPOR^. 



following the course of the vessels, around which spots are formed 

 by the deposition of dark granules, in the same manner as in the 

 potato. In the resulting rotten condition of the turnip, numerous 

 resting-spores may often be found. These resting-spores were 

 first observed by Mr. Broome, of Batheaston, who sent them to 

 Dr. Montague, who made a drawing of them. 



P. ViTicoLA. The Grape Peronospora. 



This fungus has not been observed in Britain, but as it is well- 

 known in America and latterly in France, a description is here 

 given. The mycelium is narrow, often constricted and varicose, 

 no suckers ; conidia threads stipitate, emerging in bundles from 

 the stomata, often dichotomous, and branches trifurcate. Aero, 

 spores small, ovoid, and hyaline ; oospores small and hyaline. In 

 1880, early in October, the vines in some of the French vineyards 

 presented a very unusual appearance. They were covered with 

 dry, brown, shrivelled leaves, as if they had been burnt by the sun 

 or frost-bitten, and at the extremity of the branches a few small, 

 new leaves were visible, showing a very backward condition of 

 growth. In places where the leaves were less diseased, dry 

 brown spots were visible, which spread at the expense of the 

 living tissue, ran together, and covered the whole leaf. When 

 these prematurely-dried leaves were examined, the underside was 

 seen to be covered with the white efflorescence of a mould, which 

 by-and-bye changed to a dull, leaden colour, slightly ruddy, and 

 proved to be I*, viticola. 



The disease had long been known in America, and as long ago 

 as 1877 Max Cornu called attention to the fact that the introduc- 

 tion of American stocks into French vineyards might introduce a 

 disease very much to be dreaded. In 1878 it was recognised on 

 an American vine stock, in the south-west of France ; in 1879 it 

 had reached the Rhone valley; and in 1880 it was found, as 

 above mentioned, at the north-western extremity of the culture of 

 vines in France, so that it had undoubtedly spread all over the 

 country. The question then arose as to how far this new enemy was 

 to be dreaded. According to American experience, the damage 

 occasioned by it is quite different, according to climate. In Mis- 

 souri the mildew sometimes destroys two-thirds of the crop, but in 

 that hot climate the fungus makes its appearance between the ist 



