408 PLAIN AND PLEASANT TALK 



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 /Vee^e, and sudden thawing. 



We Avould 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 ; Avhether 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, 

 restraming 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 

 sj^ring 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 



