647 



inferior vineyards. Besides the small water content, the advanced ripeness 

 of the berries is a condition which acts as a protection against sunburn. 

 The early Malinger and the early Burgundy, which ripen even in the middle 

 of August, for example, showed no injury whatever from the hot August 

 sun while more than 50 different varieties of grapes, standing close by, 

 which ripened later and therefore were still hard and green in August, had 

 suffered more or less. Measurements of the temperature in green, unripe, 

 hard berries of Riesling, Sylvaner, Elbling and late Burgundy showed 

 injury at 43 degrees C, while the fairly ripe berries of the early Malinger 

 and early Burgundy could be warmed for some time up to 55 degrees C. 

 without injury and the flesh of the Malinger grapes was killed only at a 

 temperature somewhat above 62 degrees C. 



The discovery by practical workers that sunburn is found most fre- 

 quently when wet, cold weather precedes hot days, is explained, on the one 

 hand, by the greater water content of the berries and, on the other, by a 

 lesser evaporation and, consequently, a lesser cooling when the air is moist. 

 In regard to the influence of drought, Miiller made an experiment on two 

 Riesling grapes, one of which was placed in a glass vessel lined with moist 

 blotting paper, the other in one containing some calcium chlorid, and both 

 placed in a tin case which could be heated. The grapes in moist air were 

 completely killed at a temperature of 41.5 degrees C, while those in the air, 

 dried by the calcium chlorid, were scarcely injured. Two thermometers, 

 one of which hung free while the bulb of the other was stuck into a grape 

 berry, were put in a similar tin case, and warmed up to 40 degrees C. The 

 thermometer, covered by the grape, constantly stood approximately 4 de- 

 grees lower than the other when the temperature increased slowly as well 

 as when it decreased. This may well be conditioned only by the evapora- 

 tion of the grape. 



The phenomenon of Seed cracking can set in as the result of sunburn. 

 Since, however, different causes of this phenomenon exist, it would be 

 better to consider it later by itself. 



At times so called "rusty grapes" are found, i. e., those of which the 

 skin has formed fine cork lamellae. This has been thought to be a protec- 

 tive means against sunburn^. 



Protection of the grapes by the leaves is the best precautionary method 

 and it is wrong to think grapes are helped by the removal of their foliage. 



Sun Cracks. 



In forest and other trees, at times in spring, the bark cracks. This 

 phenomenon has been named Sun cracks by de Jonghe, while Caspary- 

 considers them due to the action of frost. Surface dying of the bark is 

 distinguished, as sunburn, from simple torn wounds. Illustrations are found 



1 Zeitschr. f. Pflanzenkrankh. 1902, p. 111. 



2- Bot. Zeit. 1857, No. 10; "Bewirkt die Sonne Risse in Rinde und Holz dei- 

 Baume?" 



