74 EXPERIMENT STATION. [Jan. 



of dying back is different from that of maples. In the latter 

 the most direct channel for the conduction of water is usually 

 through a single leader, while in the elm the water is conducted 

 through several leaders. The center of a maple is therefore 

 affected first, but in the case of the elm the trouble may be no- 

 ticed in some cases on one side of the tree alone, while in others 

 the whole tree suffers. With some trees the terminal twigs and 

 branches die gradually, it requiring from three to six years for 

 the tree to collapse, while again the tree may die very suddenly. 

 Sometimes a great many of the smaller branches and the re- 

 maining branches and twigs are characterized by dense (Fig. 5) 

 tufted foliage. The black oak {Quercus ellipsoidalis) and the 

 white oak (Q. alba) are affected by winter killing in some sec- 

 tions, and an examination of the roots of numerous trees showed 

 them to be in very bad condition (Fig. G). A principal fea- 

 ture of the dying back of the oak in some localities is the pro- 

 duction of clusters of unusually large and abnormal leaves here 

 and there on the twigs and branches — the tufted foliage al- 

 ready mentioned. 



A large number of chestnut trees not affected in any way with 

 chestnut blight have the last three or four years developed stag- 

 head. While the symptoms of this dying back are not alike in 

 all cases, they are easily distinguished from those caused by 

 other agents such as gas poisoning, etc. In a majority of cases 

 trees showing this staghead effect, whether from drought or 

 winter killing, die gradually, and even when their death is more 

 or less rapid there are few of the symjitoms characteristic of gas 

 poisoning. Trees poisoned by gas usually die quickly and dis- 

 integrate rapidly ; besides, the diagnostic features to be found in 

 the tissues of trees killed by gas are entirely different. When a 

 tree is affected by gas the poisonous constituents are slowly 

 translocated from one part of the tree to the other, and the 

 symptoms of this type of injury may be easily distinguished 

 from that of other types. 



A characteristic feature of trees affected with staghead, more 

 conspicuous in slowly dying trees, may be seen in the increase 

 of the heartwood and decrease of the sapwood. A diminution 

 of the water current in the woody tissue appears to be the 

 cause of this transformation. As a consequence of this dimi- 



