64 



in the way of extended grape culture," and a summary of some points is 

 made as follows : 



The Peronospora, or mildew, which attacks the leaves on their under surface, is 

 encouraged by the atmospherical conditions accompanying dull, cloudy weather, 

 with occasional showers; or when heavy dews are deposited in positions where the 

 rays of the sun can not penetrate, or at least where the moisture can not readily 

 be evaporated. That, so far as is known, no peculiar constitution of soil or mode of 

 soil culture has any influence on its prevention. That, so far as is known, no mode 

 of pruning or training, except so far as they agree with the next paragraph, has 

 any effect in warding off the disease. That shelter and protection by covered trel- 

 lises, or masses of foliage, will greatly modify if not entirely prevent injury from 

 mildew. 



The distinguishing peculiarity of a good grape climate is, primar- 

 ily, that of an entire absence of mildew on the foliage. The pres- 

 ence of water or moisture on the leaves is necessary for the extension 

 of mildew, therefore the best grape climates in this country are those 

 of greatest immunity from dews. 



A covered grape trellis was described in the Patent Office report 

 for 1861. A trellis similar to that described was erected in the garden 

 of this Department in the spring of 1803. The grapevines grown on 

 this trellis were entirely free from mildew on the leaves and from rot in 

 the fruit, and many varieties ripened under this protection that failed 

 to mature on common trellises a few yards distant on account of the 

 failure of the leaves during summer from mildew. The philosophy of 

 the action of protection in this particular case seems to be its tendency 

 to arrest radiation of heat, thus protecting the foliage from the cooling 

 effects of night temperatures, which in turn prevents condensation of 

 atmospheric moisture on the leaves, thereby checking, to a certain 

 extent, the predisposing cause of mildew. 



In experimenting with registering thermometers it was found that 

 during clear, still nights of July, an exposed thermometer, projecting 

 four feet from the covered trellis, would mark from 6 to 10 lower 

 than would a thermometer fastened to the trellis ; the foliage being 

 thus kept warmer and drier on the protected plants, mildew was in real- 

 ity prevented. It was also found that the fruit ripened on protected 

 vines some time before that on vines not protected. 



It would therefore appear that the best grape climates or localities 

 would be those where dews were light or altogether absent. Such lo- 

 calities can be found. Indeed, it may be observed that wherever native 

 grape culture has become popular and extensive it is in localities where 

 exemption from heavy or frequent dews prevail. The localities may be 

 found either surrounded by large bodies of water or on hillsides at cer- 

 tain elevations. 



The influence of large bodies of water in ameliorating climates is 

 well authenticated, and is often turned to practical advantage in fruit 

 culture. Briefly stated, the water accumulates heat as warm weather 

 prevails* which is radiated at night, and its influence is felt on vegeta- 



