Royal Society. 69 



general appearance of this blight to the naked eye greatly resembled 

 that which appears on the peach-tree and the rose. The Douro 

 farmers had often previously noticed a similar po' branco (white 

 powder) on the vines. 



In 1851 the season was favourable, and the vines (on which we 

 had observed the blight in the previous year) were vigorous, and 

 produced perfect fruit. The vintage of 1851, throughout the Alto- 

 Douro, was excellent. In 1852 there was much wet and cold ; the 

 blight again appeared, and the vines were attacked to the extent of 

 about one in fifteen hundred. The vintage of 1852 w r as of inferior 

 quality ; but no one ascribed the failure to any disease in the vine. 

 From the autumn of 1852 until midsummer 1853, continued rain, 

 sleet, hail, and bleak winds prevailed, and in 1853 there was no 

 spring. In March of the same year the navigation of the Douro 

 was impeded, and the bar rendered impassable on account of the 

 floods ; and in April and May of the same year, prayers were offered 

 up in the churches throughout the Wine Districts for fine weather. 



In March 1854, only half-cargoes could be brought down the river 

 Douro, on account of the want of water, and rain was prayed for. 



Early in June 1853, the heat became suddenly intense, and the 

 vines had already burst forth with great vigour ; whilst, in the 

 middle of the same month, the nights became as cold as in winter. 



In the most exposed situations the vines received the greatest 

 shock ; the circulation of the sap was evidently deranged, and their 

 fruit withered as soon as it appeared. In some neighbouring vine- 

 yards, less exposed, the grapes grew no larger than peas ; they 

 were then suddenly covered with the blight (now designated the 

 Oidium), and in about three days became rotten. 



On the inclines of the mountains on either bank of the river 

 Douro, the waters had run off, and but little blight appeared. In 

 the low and heavy grounds, the most sheltered from the winds, 

 the waters remained stagnant ; yet the fruit grew to its full size, 

 and had come to maturity, when the new wood, leaves, and fruit 

 were all, to a greater or less degree, covered with the Oidium. The 

 blight sometimes attacked entire vineyards, and at other times only 

 partially affected one property, and then showed itself in others at a 

 distance — intermediate estates being for the time wholly untouched. 



It was in July 1853 that the existence of the disease in the 

 vineyards of the Douro first attracted particular attention ; but 

 many vines betrayed no unhealthy symptoms until the fruit was 

 nearly ripe. The upper part of the branches was first attacked. In 

 some instances the woody part of the young branches was speckled 

 with the Oidium, while the bunches of fruit were apparently alto- 

 gether free from it. In other instances, the grapes became touched 

 with the disease immediately before the vintage, but the woody 

 part of the brandies betrayed no such symptoms. In some vines, 

 which I supposed had altogether escaped the disease (and long 

 after the fruit was gathered and the leaves had fallen off), blotches or 

 stains, evidently the mycelium of the Oidium, appeared on the wood. 



The usual number of seeds in a black grape is two or three ; but 



