THE PEAR. 415 



summer having been dry, the growth of trees was completed 

 early, but this excess of dampness in autumn, forces the trees 

 into a vigorous second growth, which continues late. While 

 the sap vessels are still filled with their fluids, a sharp and sud- 

 den freezing takes place, or is, perhaps, repeated several times, 

 followed, in the day time, by bright sun. The descending cur- 

 rent of sap becomes thick and clammy, so as to descend with 

 difficulty ; it chokes up the sap-vessels, freezes and thaws again, 

 loses its vitality, and becomes dark and discoloured, and in some 

 cases so poisonous, as to destroy the leaves of other plants, 

 when applied to them. Here, along the inner, bark, it lodges, 

 and remains in a thick, sticky state all winter. If it happens 

 to flow down till it meets with any obstruction, and remains in 

 any considerable quantity, it freezes again beneath the bark, 

 ruptures and destroys the sap-vessels, and the bark and some of 

 the wood beneath it shrivels and dies. 



In the ensuing spring, the upward current of sap rises through 

 its ordinary channel the outer wood or alburnum the leaves 

 expand, and, for some time, nearly all the upward current being 

 taken up to form leaves and new shoots, the tree appears flou- 

 rishing. Toward the beginning of summer, however, the leaves 

 commence sending the downward current of sap to increase the 

 woody matter of the stem. This current, it will be remember- 

 ed, has to pass downward through the inner bark or liber, along 

 which still remain portions of the poisoned sap, arrested in its 

 course the previous autumn. This poison is diluted, and taken 

 up by the new downward current, distributed toward the pith, 

 and along the new layers of alburnum, thus tainting all the 

 neighbouring parts. Should any of the adjacent sap-vessels 

 have been ruptured by frost, so that the poison thus becomes 

 mixed with the still ascending current of sap, the branch above 

 it immediately turns black and dies, precisely as if poison were 

 introduced under the bark. And very frequently it is accom- 

 panied with precisely the odour of decaying frost-bitten vegeta- 

 tion.* 



very prevalent, and will be remembered, by all, as having been especially 

 the case in the autumn of 1843, which preceded the extensive blight of 

 the past season. 



* We do not know that this form of blight is common in Europe, bu ; 

 the following extract from the celebrated work of Duhamel on fruit trees, 

 published in 1768, would seem to indicate something very similar, a long 

 time ago. 



" The sap corrupted by putrid water, or the excess of manure, bursts the 

 cellular membranes in some places, extends itself between the wood and 

 the bark, which it separates, and carries its poisonous acrid influence to 

 all the neighbouring parts, like a gangrene. When it attacks the small 

 branches, they should be cut off; if it appears in the large branches or 

 body of the tree, all the cankered parts must be cut out down to the sound 

 wood, and the wound covered with composition. If the evil be produced 

 by manure or stagnant water, (and it may be produced by other causes,) 



