ATMOSPHERIC BLIGHT. 165 



effect may be the fungous growth ; the lesser, the exudation of sap from the puncture, so 

 that in these cases the effect might be mistaken for the cause. The effect of remedies may- 

 aid us materially in arriving at a correct determination of the cause. 



There is still another affection of the leaf, which results in the injury if not the death 

 of the plant. The elm, maple, chestnut, and several other trees are affected in the way 

 about to be described. Their leaves dry at the apex or on the edge, become brown, and 

 curl up. This affection may appear upon a small part of the leaf only, or it may cover the 

 whole surface of a part or all of the leaves upon a branch : if only a few leaves are dis- 

 eased, the branch will live ; if all, it dies simultaneously with the leaves ; and in some 

 instances the disease affects so many limbs, that the life of the tree is imminently threa- 

 tened. An elm standing before my door in Hudson-street has lost a part of its branches 

 every year for many years in succession. Another thrifty elm was extensively affected, and 

 most of its large branches died in the course of two weeks. The disease is the same in both 

 cases, and, I think, in all the instances which begin by the drying of the apex or margin 

 of the leaf, whatever may be the species of the tree. In no case could I find an insect to 

 which the effects could be attributed, but the affection seems to prevail most under the 

 influence of certain peculiar states of the weather ; and I have also observed, that when 

 the potato rot has been prevalent in its worst form, the trees have been most severely 

 affected with this disease. 



This disease constitutes a form of blight, which, on a close examination of the leaves 

 and limb, proves itself to be independent of the cause that sometimes produces the pear 

 blight, and which Dr. Harris ascribes to the Scolytus pyri ( Peck). The external ap- 

 pearances in the two cases are identical, and yet the causes of the blight are different : 

 in the one case, it may originate in the wounds of the insect alluded to ; but in the other, 

 there can be no doubt that it is produced by atmospheric changes resulting from heat and 

 moisture combined. Some of our elms are affected every season ; and when the cause 

 operates intensely, several kinds of trees suffer in the same way : sometimes an entire 

 limb wilts and blackens in the course of two or three days ; and then again the disease is 

 confined to a few leaves, which fall off, and the limb lives ; while in yet others the edges 

 of the leaves dry and blacken, or one half of a leaf, the other half remaining unaffected. 

 I am of opinion that we should not attribute to insects a disease that runs the course above 

 described ; and as it occurs only in certain states of the atmosphere, it is more agreeable 

 to analogy to assign the cause to which I have referred it. 



