By John Frederic Daniell, Esq. % 



to many of the processes of vegetation, and no small propor- 

 tion of what is commonly called blight, may be attributed to 

 this cause. Evaporation increases in a prodigiously rapid 

 ratio with the velocity of the wind, and any thing which 

 retards the motion of the latter, is very efficacious in dimi- 

 nishing the amount of the former ; the same surface, which 

 in a calm state of the air would exhale 100 parts of moisture, 

 would yield 125 in a moderate breeze, and 150 in a high 

 wind. The dryness of the atmosphere in spring renders 

 the effect most injurious to the tender shoots of this season 

 of the year, and the easterly winds especially are most to be 

 opposed in their course. The moisture of the air flowing 

 from any point between N. E. and S. E. inclusive is to that 

 of the air from the other quarter of the compass, in the pro- 

 portion of 814 to 907 upon an average of the whole year : and 

 it is no uncommon thing in spring for the dew-point to be 

 more than 20 degrees below the temperature of the atmos- 

 phere in the shade, and I have even seen the difference 

 amount to 30 degrees. The effect of such a degree of dry- 

 ness is parching in the extreme, and if accompanied with 

 wind is destructive to the blossoms of tender plants. The use 

 of high walls, especially upon the northern and eastern sides 

 of a garden, in checking this evil, cannot be doubtful, and in 

 the case of tender fruit trees, such screens should not be too 

 far apart. 



And here theory would suggest another precaution, which 

 I believe has never yet been adopted, but which would be 

 well worthy of a trial. When trees are trained upon a wall 

 with a southern aspect, they have the advantage of a greatly 



