578 L DISEASES F THE VINE. 



as soon as the evil is noticed early in the morning, before 

 the thaw h:is commenced. The system which is most in 

 use against the frosts of spring consists in protecting 

 the vineyards by means of artificial clouds of smoke. 

 Firewood mixed with tar, or any other material likely 

 to produce a thick smoke, is distributed in small heaps 

 at regular distances all over the vineyard, and these 

 heaps are set on fire at dawn as soon as the signs of 

 frost begin to develop. These clouds of smoke protect 

 the vines fro n frost very effectively, and various models 

 of fixed and portable apparatus are now in use in most 

 vine-growing countries, in which the clouds of smoke 

 are produced by the combustion of tar and other heavy 

 oils By the use of the pagoscope, an instrument with 

 a dry bulb and a wet bulb thermometer, a reliable 

 forecast or frosty mornings can be obtained the day 

 before, at sunset. 



Sun-stroke and heat-stroke. (M =lnpi}. This dis- 

 eased condition is met with in July and August, but 

 sometimes also earlier or later, and generally follows 

 when a long spell of calm and sultry weather with a 

 southernly breeze, is succeeded by a dry north wind. It 

 is also frequently caused directly by lively hot breezes 

 blowing from the south or south east. In any case it is 

 always brought about by a loss of equilibrium between 

 the absorbing power of the roots an i the transpiration 

 from the green parts of the plant. The affected foliage 

 becomes limp and shrivels, whole branches may die, and 

 occasionally the entire plant dies from its roots. Sun- 

 stroke or heat-stroke is more frequent on shallow clayey 

 soils which become baked and cracked in summer, but 

 occurs also on deep soils where there is no lack of 

 moisture. Sunburn or sun stroke proper is often limited 

 to the bunches which are exposed to the sun, and is 

 generally noted when the berries are still green and 

 have not yet reached full size 



