454 The Blight in the Pear Tree ; 



shrub suffers from cold in the same manner. We assert it 

 of fruit-trees because it has been observed; it must be as- 

 serted of other trees only when ascertained. 



I reply more particularly, that a mere frost is not sup- 

 posed to do the injury. The conditions under which blight 

 is supposed to originate are, a growing state of the tree, a 

 sudden /reese, and sudden thawing. 



We would here add, that many things are yet to be as- 

 certained before this theory can be considered as settled ; 

 as, the actual state of the sap after congelation, ascertained 

 by experiment ; the condition of sap-vessels, as ascertained 

 by dissection ; whether the congelation, or the thawing, or 

 both, produce the mischief; whether the character of the 

 season folloi 0171 g the fall-injury may not materially modify 

 the malignancy of the disease ; seasons that are hot, moist 

 and cloudy, propagating the evil ; and others dry, and cool, 

 restraining growth and the disease. It is to be hoped that 

 these points will be carefully investigated, not by conjec- 

 ture, but by scientific processes. 



11. We have heard it objected, that trees grafted in the 

 spring blight in the graft during the summer. If the stock 

 had been affected in the fall, blight would arise from it ; if 

 the scion had, in common with the tree from which it was 

 cut, been injured, blight must arise from it. 



Blight is frequently caused in the nursery ; and the cul- 

 tivator, who has brought trees from a distance, and with 

 much expense, has scarcely planted them before they show 

 blight and die. 



12. It is objected, that while only a single branch is at first 

 affected, the evil is imparted to the whole tree; not onlx'" to 

 the wood of the last year, but to the old branches. I re- 

 ply, that if a single branch only should be affected by fall- 

 frost, and be so severely affected as to become a repository 

 of much malignant fluid, it might gradually enter the sys- 

 tem of the whole tree, through the circulation. This fact 

 shows why cutting is a partial remedy ; every diseased 

 branch removed, removes so much poison ; it shows also 

 why cutting from below the seat of the disease (as if to fall 

 below the haunt of a supposed insect,) is beneficial. The 

 farther the cut is made from that point where the sap has 

 clogged the passages, the less of it will remain to enter the 

 circulation. 



13. Trees of great vigor of constitution, m whose system 



