REPORT OF THE DIRECTOR I913 8l 



The maple is well known as a very shallow rooted tree and the 

 effect of the dry wind upon transpiration in the leaves is very 

 marked in the case of any tree. It is apparent that the period of 

 drought preceding the early part of July had reduced the available 

 water of the soil to a minimum, so that the factors favoring trans- 

 piration (that is, dry, hot winds) which followed, greatly exceeded 

 the power of the trees to absorb water from the soil which was 

 actually deficient in moisture. Such a condition of affairs was 

 particularly active in the case of maples along streets, highways, 

 in parks or other situations where the soil was not protected by 

 litter or undergrowth from drying out. 



The leaves of the maple being unable to maintain the high rate of 

 transpiration necessary under such conditions, were susceptible to 

 the chemical activity of the sun's rays, causing the bronzing effect, 

 a chemical change of the cell contents, somewhat analogous to what 

 takes place normally in autumn when the leaves turn to shades of 

 red or yellow. In many cases this state was followed by withering 

 and death of the leaves, as sufficient moisture was not available to 

 revive the leaves and to maintain their turgidity, which alone keeps 

 them under ordinary conditions from collapsing. 



That the dry weather and dry winds mentioned were responsible 

 for the widespread damage seems probable also from the fact that 

 the trees in situations of permanently damp soil, as in deep wood- 

 lands, suffered little or not at all; and of the trees affected, the 

 greatest damage seems to have been on the side exposed most di- 

 rectly to the wind. Elms, having deeper-going roots, did not suffer 

 so much as the maples, although considerable damage to their foliage 

 was noticed in the case of some trees growing in dry soils. The 

 leaves of the elm also possess a thicker epidermis and are better 

 adapted by structure to withstand the factors like wind and heat 

 which favor excessive transpiration and its subsequent damage. 



The injury to maple and elm foliage thus noted is not likely to be 

 permanent, nor is it likely that the trees thus affected will suffer 

 from more than a slight setback. The damage consists chiefly in 

 the unsightly appearance of the foliage. Local and even wide- 

 spread occurrence of this sort of damage has frequently been re- 

 ported in former years but not with such severity as during the 

 past season. 



A new fungus enemy of the maple. Several ornamental sugar 

 maples at Glen Cove were observed by Mr F. E. Willets to be 

 suffering from the attack of a fungus which caused the death of 

 numerous twigs and branches, so that by August the trees were 



