234 CULTURE OF THE GRAPE. 



is exposed in the greatest degree to the effects of dew is 

 obvious. Copings and projecting cornices have, in num- 

 berless instances, proved a safeguard against mildew. A 

 single, wide board has been run along the top of per- 

 pendicular trellises for the purpose of keeping off the 

 dew ; and it has been thought to effect good results. 

 Whether such results are not rather the effect of protec- 

 tion from cold, and a partial arrest of warm air radiating 

 from the earth, may be a question. In the cases of Prof. 

 Silliman and Mr. Riehl, and such cases might be multi- 

 plied, it is important to determine whether the evil 

 result of bringing vines out from a projecting coping is 

 caused by the new exposure to strong currents of air, and 

 the extremes of heat by day and cold by night, rather 

 than by the effect of dew. It is a question which must 

 be determined by facts alone. * I have hope that a vine 

 trained horizontally, near the ground, will of itself arrest 

 radiation to some extent ; that it will, to some extent, 

 find a benefit in its proximity to -the earth, the tempera- 

 ture of which is so much above the cold night-air. We 

 know this benefit is very appreciable where vines run 

 over rocks, which become heated during the day, and give 

 off* their heat during the night. It must be kept in mind 

 that the leaves spoken of by Prof. Silliman were high in 



