1912.] PUBLIC D0CUMP:NT — No. 31. 55 



Sun scorch is common to numy plants, and is referred to 

 under dilfcrent names such as ^' topburn " in lettuce, "tip- 

 burn " of potatoes, " leaf burn," " wilt," etc. It may result 

 from the presence of certain chemical substances in the soil, 

 or from some individual peculiarity in the root-absorptive 

 capacity of the organism. The peculiar drying and reddening 

 of the cells of the maple leaves which we have previously re- 

 ferred to as " bronzing " is not necessarily caused by wind ; 

 the principal factors necessary being a soil deficient in mois- 

 ture, and excessive transpiration. 



As already stated, " bronzing " occurs on very hot, dry days, 

 in periods of severe drought, and this last summer we have 

 succeeded in producing many excellent examples of it in the 

 greenhouse. The trouble was very common this season, our 

 attention often being called to it, and we have been observing 

 very severe cases of it in certain maple trees for many years. 



