54 EXPERIMENT STATION. [Jan. 



as they would die in turn. Had it been possible to prune these 

 roots, their dying back could have been checked, a new system of 

 secondary roots would ha^•e formed and the tree would have re- 

 covered. Oak trees in this condition have been fairly common 

 in certain parts of eastern Massachusetts for the past few years, 

 and many more will show the same symptoms later. 



Another trouble which has been more or less common the last 

 few years is known as sun scald of maples. This is responsible 

 for injuring many valuable shade trees. On one avenue we 

 recently observed 16 rock maples killed by sun scald. This af- 

 fects the trunks and limbs on the side of the tree exposed to the 

 sun. It is characterized by a drying up of the bark, which al- 

 most immediately becomes affected with a canker fungus {Nec- 

 iria cinnabarina, Er.). On smaller trees sun scald often kills 

 the whole trunk. Generally only one side of the tree is affected, 

 and occasionally one or more branches. The root system is not 

 affected by sun scald, and limbs are much less likely to be af- 

 fected than the trunk. The fact that the root system is not af- 

 fected by Sim scald, and that the bark usually becomes infected 

 with Nccfria, makes it easy to distingiiish this type of injury 

 from that caused by gas poisoning, since in this case the Nectria 

 never appears, but, instead, profuse growths of Schizophyllum 

 and Polystida are present. Very similar effects are produced 

 on the trunk when the tree is sprayed with kerosene or crude 

 oils, since Nectria almost always accompanies such injury. 



Sun scorch differs from sun scald very materially, as it af- 

 fects only the foliage. This is very common on maples, and in 

 recent years the white pine has been affected in this State. Sun 

 scorch foHows dry periods, and is usually associated with strong, 

 drying winds, lack of water in the soil, etc. ; in fact, it may be 

 caused by various abnormal functions of the root system. It 

 hardly ever completely defoliates trees, and on maples it simply 

 l)urns the foliage, particularly on the windward side. Various 

 conifers, such as arbor vitscs, when grown in dry soil invariably 

 show sun scorch in the spring, particularly when there are dry- 

 ing winds nnd the ground is frozen. P^or many years past we 

 have received a large number of inquiries concerning the effects 

 of sun scorch on maples. These effects resemble those of leaf 



