54 EXPERIMENT STATION. [Jan. 



BRONZING OF MAPLE LEAVES. 



G. E. STONE. 



A somewhat common and peculiar effect on rock maple 

 leaves, especially noticeable in very hot and dry summers, was 

 brought to our attention this past summer. We have noticed 

 this trouble many times before, particularly on rock maples 

 growing in certain characteristic soils or habitats. It is most 

 commonly seen on maples growing in dry soil where there is 

 insufficient soil-moisture during periods of extreme drought. 



The trouble is characterized by an absence of the typical 

 maple leaf green. The leaves are more or less rigid, and in 

 color are light, with a reddish brown tinge. An examination 

 of the surface of the leaf with a hand lens, or even with the 

 naked eye plainly shows that many of the cells of the leaf 

 blade or lamina are dead and reddish browm in color. These 

 dead cells are confined to certain areas of the laminae, mainly 

 between the minute veinlets, whereas those cells near the vein- 

 lets are green and alive. 



Repeated examination of the leaves has demonstrated that 

 the trouble is caused by no pathogenic organism, but is purely 

 functional in nature. On the other hand, it is quite distinct 

 from the so-called sun scorch so commonly affecting the rock 

 maple, although both are induced by similar conditions. The 

 typical sun scorch is characterized by more or less irregular 

 blotches of dead tissue more often on the edges of the leaves, 

 which are usually more susceptible to the scorching and are 

 often lacerated severely. This sun scorch, like the ^' bronzing," 

 also affects maples growing in very dry soil, on dry, windy 

 days, when the roots cannot supply the foliage with sufficient 

 water. Since transpiration under such conditions is very active 

 and root absorption limited, wilting and death of the leaf 

 tissues result. 



