MICHIGAN ACADEMY OF SCIENCE. 333 



aud from these leaves as foci the disease spread to the fruit. Many sprayed 

 orchards, because of untiiueliness of spraying, obtained a poor control of scab. 

 In a similar manner, cherry leaf spot, brown rot of plum, and wheat rust 

 were serioiis diseases in a year when a glance at the weather map would 

 indicate that diseases should be checked. 



It is significant that with a wide range of diseases, the weather during 

 the time of the establishment of the primary and secondary infections is the 

 significant factor deciding on the severity of loss. This has already' been 

 pointed out for late blight of potatoes, and is a principle of great significance 

 on a wide range of diseases. 



WEATHER INJURY TO PLANTS. 



The season of 1918 was important in that it brought to the attention a few 

 specific types of weather injury which had previously not been emphasized 

 in the literature. In the past, a variety of serious fruit and leaf deforma- 

 tions have been ascribed to weather injury. All are familiar with frost effects 

 on fruits and leaves. Similarly on forest trees, especially hard maples, a type 

 of tip turn of the leaf has come to the laboratory every dry year. This 

 trouble, simulating anthracnose sligt tly, is found in both city and forest trees 

 alike, and has generally been assigned to physiological breakdown incident to 

 drought conditions and lack of water. The similarity of this trouble to potato 

 tip burn has often been postulated and it will be interesting to note if in the 

 same way this leaf firing, long ascribed to weather, can be shown to be 

 related to leaf hopper attack. 



In early June, oats which were in extremely succulent and tender condi- 

 tion, were badly injured by liot, dry winds. Within a day or two the labora- 

 tory was flooded with specimens from all parts of the state, asking the cause 

 of the new bliglit which came on so suddenly. 



It was characteristic of the wind injury, that other grains escaped injury, 

 with the iM>ssible exception of barley, but tlie oats were withered anil scorched 

 badly. The exposed leaves mei'ely dried up. Tliis condition was rapidly out- 

 gntwn iiiid the fields have grown and apparently suffered no loss. 



.Another efTeet of the hot, dry winds, but later in the season, was the 

 deformation of apples. AVhile various varieties showed the trouble, only those 

 on exposed parts of the tree showed the injury. The effect produced by the. 

 hot winds and hot sun are shown iii the picture. It will be noted that the net 

 result was to produce girdled, conical apples. The flesh under the shrunken 

 portion was found to be dry and cork-like. 



Tiiis trouble, which is allied to "Cork"*, was believed to be due to lirynJ^ss 

 and wind injury. The following varieties showed the injury; it is evideiit 

 that stage of maturity was not fe.sijfecially significant in tiiis injury, since the 

 iipltles injured wert; of vuryiny size and variety: 



*Coon««. a. M. Mich ^ta. Hprc Bui »5 : U'.Jl, IttlS. 

 «&t<i, A. J. N. T. (Opti"Vii) 8U. HtJl, i2* . 



