THE PEAR. 416 
summer having been dry, the growth of trees was zompleted 
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 dber, 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 1848, which preceded the extensive blight of 
the past season. ; 
' * We do not know that this form of blight is commor. 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. 
a 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 
vody 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 
Roy manure or stagnant water, (and it may be produced by other causes,) 
