ATMOSPHERIC BLIGHT. 165 



effect may be the fiine;ous (growth ; the lesser, the exvulalion of sap from the punetiire, so 

 that in these eases tlie ell'ect niisht be mistaken lur the cause. The ett'ect of lemeiiies may 

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



There is still anotlier aflection of the leaf, which results in the injury if not the death 

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

 al>out to he described. Their leaves dry at the apex or on the edge, become brown, and 

 ciu-1 up. This affection may appear upon a small part of the leaf only, or it may cover the 

 whole surface of a i)art 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 

 ca.ses, and, I think, in all the instances which begin by the (hying of the ape.\ or margin 

 of the le«f, wliatever 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 bliglit, 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 Sco/ytus 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 l)y 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 unafftcled. 

 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. 



