106 GENERAL REMARKS 



on the nature or identity of two diseases. The excision of (he dead or dying limb contain- 

 ing the little depredator, and burning ii, assuredly puts an immediate stop tu the progress 

 o( this kind of l)liglit, as it has bfon termed, while the knifi" very rnroly has the same 

 salutary influence in the true Might. The term blight, is also applied to a diseased condi- 

 tion of tiie plum tree, and which is al;o the effect of an insect in its larva or grub state, 

 nestling iu the branches and producing an exudation of gum in part, and a fungous growth 

 of wood, which turns black the second year after the injury. This too is cured by excision ; 

 though it is often left until so many branches are affected that the tree must suffer great 

 mutilation in order to remove all the affected branches. Yet it is the only way to treat it. 

 I may add to this also, the attacks of the leaf-rollers. Tl'ey destroy the young leaves, and 

 may be the youi'g branches too, which finally turn brown or black. 



The true blight, however, cannot be traced to injuries by insects. Or at least we may 

 say that there is a disease as independent of these as that of the yellows in peach trees. 



We would confine the term blight to that disease which seems to stand as a consequent 

 to certain atmospheric conditions. 



To atmospheric causes we may superadd a rapid growth by a superabuiidance of sap or 

 of circulating fluids. I think this view is sustained by the fact that limbs of a rapid growth 

 or young tlirifty growing trees have generally suffered more thad those of a slow growth, 

 and whose texture is apparently more firm and compact. It is true, however, that the dis- 

 ease of fruit trees, which is usually known as the blight, by no means stands in striking 

 contrast with the potato disease. In fact many of the phenomena of each are quite simi- 

 lar, both in appearance and in their ultimate results. 



The potato disease commences in the leaf and stem,* beginning with a drying of the 

 former upon its edges, and extending rapidly through the whole texture. The same effects 

 follow with all the leaves in quick succession, and sometimes, when the cause acts intense- 

 ly, the stems and leaves become perfectly brown and crisp in a few hours. The same 

 changes take place in the blight of fruit trees; first a leaf becomes brown and crisp, or 

 several of them are attacked simultaneously, and the first thing which attracts oiu: notice 

 is the perfect death of a small branch which hangs down in the midst of a perfectly healthy 

 vegetation. 



The disease may commence in the middle of a large limb and extend both ways, and 

 it often happens that the termination of the branch, the newly formed wood, is the last to 

 die. If a limb partially destroyed by the blight is closely inspected, the following pheno- 

 mena may be usually observed. Patches of brownish bark on the sides of the limb. These do 

 not extend entirely around it, and they may appear at irregular distances, and are separated 

 from each other by living bark, but they soon coalesce and extend around the limb, as 

 well as in the direction of the base and apex. But accompanying the death of the bark of 

 the limb, there is also the death of the apex of the expanding leaf buds. If these are 



*Suba«quent examinations of diseased potatoes, seem rather to sustain the view that the disease manifests itself in 

 the Item near the tuber, where it becomes dry and finally soft, even while the leaves are fresh and green. 



