MYCOLOGICAL SECTION. 105 



Five kilograms of the powder is about the quantity required for 

 an acre of vines. It is applied with an ordinary sulphuring-bellows. 



The value of the Bordeaux mixture, or, as we have come to term 

 it, the copper mixture of Gironde, has been settled beyond dispute, 

 but there are certain factors which may determine the degree of the 

 success in its use which ought to be considered. These are, the care- 

 ful preparation of the mixture ; the time of its application ; the more 

 or less intelligent manner in which the spraying has been made ; the 

 atmospheric conditions of rain or dryness existing at the time or 

 which may follow the operation ; the number of treatments made ; 

 and the purity of the sulphate of copper used. 



These are all points which should be carefully noted in experi- 

 menting with this and the other remedies proposed, especially in de- 

 termining their relative value as fungicides. 



In the hands of some grape-growers a remedy may seem to_ give 

 excellent results, but before it receives unqualified recommendation it 

 must be tried in many localities and during a series of years, in order 

 to eliminate all sources of error. Many cases of apparent benefit 

 from the aj)plications may be solely due to accident, such as changes 

 in the weather or some other cause not within the control of the 

 grower. If applications are made to the vines in years when, from 

 dryness or other natural cause, fungi of all sorts are unusually scarce, 

 then, unless very carefully conducted control experiments are made 

 at the same time, it is easy to see how results due solely to the season 

 or location might be ascribed to the remedy, and false conclusions 

 arise. Hasty generalizations from a few observations and experi- 

 ments are very common, but the careful investigator will not be de- 

 ceived by them. In reference to all proposed remedies, it may be 

 said only when the disappearance of the fungus uniformly follows 

 the application of the remedy, are we warranted in attributing this 

 to its use. 



II.— The Powdery Mildew. 



Uncinula spiralis^ B. and C. 



(Plate II.) 



Like the Downy Mildew, the Powdery Mildew of the vine is a 

 native of this country, and attacks the foliage, young shoots, and 

 berries of both the wild and cultivated varieties of the grape, show- 

 ing a decided preference to those of the Vinifera class. Here the re- 

 semblance ceases, however, for the Uncinula is a fungus of a very 

 different habit of growth from the Peronospora, and belongs to an 

 entirely distinct group of parasites — a group embracing what are 

 familiarly referred to as the White Mildews or Blights, of which th^ 

 common Grass Mildew (Erysiphe gimminis), the Lilac Mildew {Mi- 

 crospliceria Friesii), and the too well known Mildew of the Hop-vine 

 are examples. The diversity extends even to the climatic conditions 

 favoring the growth of these two fungi; for, while a liberal supply 

 of moisture is necessary to the full development of the Peronspora, 

 the Uncinula likes a comparatively dry atmosphere, and always oc- 

 casions most injury during seasons of protracted drought. It has 

 long been known as a serious pest in California, and is nowhere en- 

 tirely absent in the region east of the Mississippi. In the average 

 season, however, it does comparatively little injury in the open vine- 



