BLIGHT IN THE PEAR TREE. 



61 



the branch shrivels and turns black ; and 

 finally, if the dose is large enough, the whole 

 tree dies. 



That the sap of trees is often wholly 

 changed in its nature by the cold, any one 

 who examined the state of the peach and 

 many other fruit trees, in the spring of 1836, 

 after the extraordinary and unparallelled 

 winter of 1835, will easily understand. 

 Thousands of trees, always hardy before, 

 were destroyed outright by the excessive 

 cold of that winter. In all cases, the sap 

 vessels were more or less distended or burst ; 

 the matter contained in them became gluti- 

 nous, dark coloured, and, in some cases, 

 offensive to the smell. Nearly all the trees 

 which presented this appearance during the 

 spring, died before the autumn of the same 

 year. 



What we call the frozen-sap blight, is not 

 confined to the pear tree alone. We have 

 seen it in several other trees not entirely 

 hardy in this latitude, or which suffer from 

 winters of unusual severity. Such are the 

 Ailanthus, the Catalpa, and the Spanish 

 Chestnut. The latter tree, especially, shows 

 very frequently, while standing in the nur- 

 series and still young, the same symptoms 

 as the blighted pear tree. First, early in 

 the spring, patches of shrivelled and dis- 

 coloured bark near the lower part of the 

 trunk ; second, about the beginning of sum- 

 mer, sudden withering of the foliage, death 

 of the branches, and often of the whole tree. 



A most important question, which we 

 now reach, is this : Are these diseased spots, 

 where the malady first arises, and from 

 whence it is disseminated, the immediate 

 effect of the freezing, or the thawing ? 



We think we are prepared to answer 

 this question. The fact that these spots, 

 when they occur on the trunk or larger 

 branches, almost invariably appear on the 

 southern side, proves clearly that it is the 



too rapid thaioz)ig caused by the sun's rays, 

 which bursts the sap vessels, and is the im- 

 mediate cause of the alteration in the 

 matter deposited in them. Were it the 

 effect of the frost simply, the evidences 

 would appear equally on all sides of the 

 trunk. 



Again, it is well known to all who have 

 the care of half-hardy trees or plants, that 

 if shielded from the direct action of the 

 sun's rays, either by a mere shading of 

 boards, or by placing them in a northern 

 exposure, they do not suffer in the least, even 

 by a temperature much colder than that 

 which destro3-s the same trees when planted 

 in a sunny southern exposure. A plant, in 

 other words, will bear, without injury, a very 

 severe frost, if it is not, directly afterwards, 

 exposed to a sudden thawing. 



Now the pear tree appears, so far as re- 

 gards its bark, to be the most tender of our 

 fruit trees. Our climate in Avinter is often 

 one of the most sudden and extreme varia- 

 bleness. To-night we have the thermome- 

 ter at zero of Fahrenheit ; the next morning 

 we have a bright unclouded sun, that shines 

 on any dark object exposed to it, with all 

 the warmth of April. The consequence to 

 a susceptible tree is obvious. Any part 

 which happens to be especially exposed, 

 either from its position, as upon the south- 

 ern side of the trunk, or from the circum- 

 stance of the lodgment of any unusual 

 deposit of juices therein, is of course most 

 likely to suffer from the sudden and pow- 

 erful effects of the sun immediately after 

 severe frost. Here, accordingly, we soon 

 find the sap vessels burst, the bark shri- 

 velled, and the poisoned matter accumulated, 

 which is the source of the bliglit of the en- 

 suing spring and summer. 



What is the remedy for the frozen'Sap 

 blight 1 



For the bliecht in its milder forms, as we 



