408 PLAIN AND PLEASANT TAXK 



the tree is spent before autumn, and it is going to rest 

 when frost strikes it. 



10. It may be inquired why fall-growing shrubs are not 

 always blighted, since many kinds are invariably caught by 

 the frost in a growing state. 



We reply, first, that we are not to say that every tree or 

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

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

 asserted of other trees only when ascertained. 



We 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 freeze, and sudden thawing. 



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

 ascertained 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 following 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 dsease. 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 



