646 



of ripening at a time when the fruit should really be storing up reserve 

 substances. The result is that the cells of the fruit flesh, insufficiently filled 

 with reserve substances, end their life prematurely, resulting in a specked 

 condition and premature decay when stored. In grains, a premature 

 ripening of the blades causes a distinct injury to the kernel from an insuffi- 

 cient formation of starch'. 



• The other form of injury consists in the direct killing of the tissues, 

 by sunburn, on the exposed places of juicy fruits. Such burned spots fre- 

 quently resemble places injured by hail because the killed tissue cannot 

 stretch proportionately during the process of swelling of the fruit and 

 therefore tears. In the increasing cultivation of the tomato, we now find 

 abundant examples which remain unrecognized only because fungi usually 

 infest the burned places of the fruit. The cases are then described as 

 parasitic diseases. 



Injury to Grapes from Sunburn. 



This is of great agricultural significance. According to Muller- 

 Thurgau's observations- an injury to grapes will be observed when hot, 

 clear, sunny days occur suddenly after a longer period of cold, damp 

 weather. It is found then, almost as a rule, that the berries of the free 

 hanging clusters, exposed to the direct rays of the sun, lose their green 

 color, become pale, then turn brown and finally shrivel. The stem of the 

 cluster also begins to suffer where it is directly touched by the sun's rays. 

 The berries, hanging to it, shrivel but, in this case, do not lose their green 

 colon. In the blue varieties, the berries, which come in contact with the 

 sun's rays, remain green, becoming darker than those of the white varieties 

 and turn almost black. In some years, whole bunches are found shrivelled 

 up like raisins, producing in places a considerable injury^. That it is 

 actually an excess of the heat which kills the berries in this case is shown 

 by the fact that grapes, which were warmed in a tin case to 50 degrees C, 

 took on exactly the same appearance as specimens attacked by sunburn out 

 of doors. The state of ripeness, as well as the water content of the organs, 

 and also the humidity of the surrounding air, exercises a decisive influence 

 on the burning. Unripe Riesling and Sylvaner berries were not injured 

 when warmed to 42 degrees C, for two hours but were injured at 44 degrees 

 C; after an equal length of time. 



Direct measurements showed that the berries, on which the sun shone, 

 were warmer than the surrounding air. While a thermometer in the air 

 showed 24 degrees C. in the shade and another 36 degrees C. in the sun, the 

 temperature in the grapes, exposed to the sun, increased to 40 degrees C. 



It was found further that Riesling grapes from good warm positions 

 were poorer in water and suffered less from sunburn, than those from 



1 D6h6rain et Dupont, Uber den Ursprung dcr Starke des Weizcnkorns; cit. 

 Biedermann's Centralbl. 1902, p. 324. 



2 Der Weinbau 1883, No. 35. 



3 Jahresber, d. Sonderaussch. f. I'flanzenschutz 1892. Arb. d. D. Landw. G. 



