194 



Blight in Pear Trees. 



IX. 



evi], i. e., the place where the bark is dis- 

 eased or dead, is lower down and on old 

 wood. Certainly, it should be; for the re- 

 turning- sap falls some ways down before it 

 effects a lodg-einent. 



It may be said that spring frosts might 

 produce this disease. But in the spring of 

 1834, in the last of May, after tlie forest 

 trees were in full leaf, there came frost so 

 severe as to cut every leaf; and to this day 

 the dead tops of the beech attest the power 

 of the frost. But no blight occurred that 

 year in orchard, garden, or nursery. 



It may be asked why forest trees do 

 not suffer. To some extent they do. But 

 usually the dense shade preserves the moist- 

 ure of the soil, and favours an equal growth 

 during the spring and summer; so that the 

 excitability of the tree is spent before au- 

 tumn, and it is going to rest when frosts 

 strike it. 



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. 



I 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 ascer- 

 tained. 



I reply more particularly, that a mere 

 frost is not supposed to do the injury. The 

 conditions under whicli 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 

 j'et to be ascertained before this theory can 

 be considered as settled ; as, the actual state 

 of the sap afler congelation, ascertained by 

 experiment; the condition of sap-vessels, as 

 ascertained by dissection : whether the con- 

 gelation, 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 dis- 

 ease ; 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 care- 

 fully investigated, not by conjecture, but by 

 scientific processes. 



We have heard it objected, that trees 

 grafted in the spring, blight in the graft 

 during the summer. If the stock had been 

 af!ected 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 nurse- 

 ry ; and the cultivator, who has brought trees 

 from a distance, and with much expense, 



has scarcely planted them before they show 

 blight and die. 



It is objected, that while only a sin- 

 gle branch is at first afiected, the evil is im- 

 parted to the whole tree ; not only to the 

 wood of the la^t year, but to the old branches. 

 I re])ly, that if a single branch only should 

 be atiected by fall-frost, and be so severely 

 affected as to become a repository of much 

 malignant fluid, it might gradually enter the 

 system of the wliole tree, through the cir- 

 culation. This fact shows why cutting is a 

 partial remedy; every diseased branch re- 

 moved, 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 further 

 the cut is made from that point where the 

 sap has clogged the passages, the less of it 

 will remain to enter the circulation. 



Trees of great vigor of constitution, 

 in whose system but little poison exists, may 

 succeed after a while in rejecting the evil, 

 and recover. Where much enters the sys- 

 tem, the tree must die: and with a sudden- 

 ness proportioned to the amount of poison 

 circulated. 



A rich and dry soil would be likely to 

 promote early growth, and the tree would 

 finish its work in time ; but a rich and moist 

 soil, by forcing the growth, would prepare 

 the tree for blight; so that rich soils may 

 prevent or prepare for the blight, and the 

 difference will be, the difference of the re- 

 spective soils in producing an early instead 

 of a late growth. 



So long as the blight was believed to be 

 of insect origin, it appeared totally irreme- 

 diable. If the foregoing reasoning be found 

 correct, it will be plain that the scourge 

 can only be occasional ; that it may be in a 

 tlegree prevented, and to some extent reme- 

 died where it exists. 



We should begin by selecting for pear or- 

 chards a warm, light, rich, dry and early 

 soil. This will secure an early growth and 

 ripe wood, before winter sets in. 



So soon as observation has determined 

 what kinds are naturally early growers and 

 early ripeners of wood, such should be se- 

 lected; as they will be least likely to come 

 under those conditions in which blight oc- 

 curs. 



Wherever orchards are already planted, 

 or where a choice in soils cannot be had, 

 the cultivator may know by the last of Au- 

 gust or September, whether a fall growth is 

 to be expected. To prevent it, I suggest 

 immediate root-pruning. This will benefit 

 the tree, at any rate; and will probably, by 

 immediately restraining growth, prevent 

 blight. 



