158 MANUAL OF MODERN VITICULTURE. 



prevent draughts, and, therefore, help the production oi 

 this phenomenon; also avoid cultivating between the vines,, 

 as it increases the radiating surface. 



A temporary means of protecting vines consists in cover- 

 ing them with a screen preventing radiation from the soil 

 towards the sky, and from the vines towards the soil. Dr. 

 J. Guyot* recommends the use of screens made of straw 

 resting on the stakes, which are used with his system of 

 pruning. He indicated an ingenious arrangement allowing 

 the use of these screens as a preventive of non-setting, &c.. 

 The disadvantage of this system is the high annual expense, 

 which Guyot estimated at 8 per acre, and further, high winds, 

 which may displace the screens and break a great number 

 of young shoots. These remarks also apply to Du Breuil's 

 system,t in which canvas is used, or to Jobard's system, con- 

 sisting in oiled paper hoods fixed over the vines. An efficient 

 and much cheaper shelter is often attained by tying a handful 

 of straw on the stake, and spreading it so as to forma hood;- 

 this diminishes the intensity of the radiation. 



Artificial clouds are also used with success to prevent the 

 action of white frosts. These are obtained by burning 

 matters producing an abundant smoke. 



The matters most used are manure, green grass, dry leaves, 

 burnt over straw or bushes. The addition of coal tar or 

 oil, by-product of the manufacture of gas, which gives a 

 fuliginous flame, increases the smoke. The oil can also be 

 lighted in tins, &c., distributed regularly in the vineyard. When 

 the air is still (which is a necessary condition for the pro- 

 duction of white frost) the smoke spreads horizontally, and 

 its thickness prevents the effects of the radiation, forcing the 

 thaw^to take place slowly by sheltering the ground from the 

 first rays of the sun. One of the difficulties resides in the 

 fact that it is necessary to obtain constant supervision by the 

 man in charge of the fires, which have to be lighted at oppor- 

 tune times ; but electric thermometers have been invented,! 

 which are placed in the vineyard, and by means of an electric 

 battery cause a bell to ring when the thermometer falls to a 

 degree determined beforehand. Lestelle has improved this 

 system by adding an automatic lighter. 



*Dr. Guyot. Culture of the Vine and Wine-making. Translated by L. Marie, pages 

 24-30 and 40-44. Melbourne, 1865. [Transls.] 



t A. du Breuil, Vineyard Culture, translated by John A. Warder, pages 263-273, 

 Cincinnati, Ohio, 1867. [Transls.] 



J Lemaire-Fournier's alarm thermometer has been used su ccessfully at the School of 

 Agriculture, at Montpellier. 



Jour, d'agric. prat., 1884. Vol. II., page 557. 



