230 BOARD OF AGRICULTURE. 



they are growing. They remain dormant during the winter, 

 and when spring comes germinate, and make their wa}'- into 

 the nearest grape-vines. It would not be unwise in the autumn 

 to collect and burn all grape-leaves — that is, as far as prac- 

 ticable — in districts which have during the summer suffered 

 from the Uncinula. In this place we should bear in mind 

 what was said of the black knot extending from wild species 

 to cultivated. The Uncinula can extend in a similar way, as 

 it is found on wild vines ; but, as far as we yet know, the 

 fungus does not grow on any wild plants except grape-vines. 



If we turn now to the Peronospora which grows on grape- 

 vines, we see that the preventive measures, which in the case 

 of the Uncinula would be of advantage, would here be of 

 little avail ; because the fungus is not confined to the surface, 

 but pervades the whole plant, and, in fact, does not grow 

 through the breathing-pores into the air until it has already 

 traversed a considerable part of the interior of the leaves 

 and stems. The first warning of the presence of the fungus, 

 viz., the white spots on the under surface of the leaves, is not 

 to be interpreted as showing that the disease is beginning, 

 but that it is already far advanced. To sprinkle sulphur on 

 the leaves is quite useless in the case of the Peronospora ; for it 

 will not affect the mass of the fungus which is in the interior. 

 The only thing which will check the disease is to diminish 

 the moisture in the air ; but that, unfortunately, is bej^ond 

 human control. If the season happens to be dry, all very 

 well : if very wet, then the Peronospora^ once started, will 

 grow in spite of every thing. 



The disease spreads from plant to plant during the summer 

 by means of the conidial spores. They may be carried about 

 by the wind and rain, just as the conidial spores of the Unci- 

 nula ; but, when they fall on a place sufficiently moist, they 

 germinate, but in a different way from the conidial spores of 

 Uncinula. The cc itents of the spores separate into a number 

 of distinct bodies, which break through one end of the spore, 

 and escape, leaving the empty spore-wall behind. The bodies 

 which escape, to which the name of " zoospores " is applied, 

 swim about by means of two hair-like threads called " cilia," 

 which are in constant motion. Being very small, they are 

 able to move about in the moisture which is found on the 

 ground and on plants when it is not dry weather. They 



