SCREENS AGAINST WIND. 



189 



Pig. XXXI. 



currents of air, and thus diminish the amount of perspiration by 

 two opposite methods. 



For screening plants from dry winds various means are employed, of 

 which the following is a good example. In Prance a basket is 

 employed, composed of two moveable semi-cylinders, 

 constructed in the way of straw hives. To these 

 semi-cylinders are fixed soUd feet of wood, for the 

 purpose of being driven into the ground. If it is 

 only necessary to shelter one plant from east or 

 north-east winds, one semi-cylinder is sufficient ; but 

 if it is a plant which you are forced to protect, is 

 delicate, and requires a more complete protection, you 

 inclose it between the, two semi-cylinders fixed one to 

 the other by means of hooks represented in the 

 drawing. A lid of the same construction, furnished 

 at its edge with a circle in woodwork, is fitted, when 

 necessary, upon the cylinder, and thus, perhaps, 

 offers a more effectual shelter against the severity of 

 cold winds and excessive heat than any other. These 

 sorts of shades are light to move, very solid, and 

 very warm; for, letting but little of the exterior 

 air penetrate, they preserve at night the heat which 

 accumulates in the interior. They also guard plants well from the 

 action of sun, and thus offer a means of checking the natural 

 perspiration of green parts. 



The following table, for which I am again indebted to Mr. 

 Thompson, wiU be found to show that the average degree of 

 dryness, in the middle of the day, throughout the year, is, 

 with a — 



Degrees Amount 

 of Dryness, of Moisture. 



North, wind 6-55 = 816 



North-east V-30 = "794 



East 6-20 = 825 



Average, with wind from the three ) 



coldest points ..'...'...) ^'^^ " ^" 



South wiad 4-23 = 877 



South-west . ■ 4-70 = 859 



"West 6-20 = 733 



Average, with wind from the thfee ) _ 



warmest points ." ) 



