B54 PRINCIPLES OF BOTANY, ETC. 
»§ 328. 
Carcinoiia arborum, or a cancerous affection, oc- 
curs principally in fruit-trees, when’ they lose too 
much gum, and this undergoes an acetous fermen- 
tation. A ‘great spongy excrescence rises, which 
even in the driest weather discharges an acrid ichor, 
which corrodes every thing. We have two distinct 
species, the open and the latent cancer. » The first 
species is easily seen, and cured by simply extir- 
pating the affected part.’ But the second species 
may have'spread far in length and breadth, before 
it can be discovered. \ Then we must hasten to save 
the tree, the cancerous parts. must be taken off, and 
Forsyth’s cement afterwards applied to it. 
To prevent the disease, change of place and good 
care, to obviate too much formation of oe in fruit- 
trees, willprove' beneficial. 
§ 329. 
Necrosis, or dry gangrene, is that disease which 
makes the leaves or other parts to grow black and 
bonate of lime, till the surface of the cement is as smooth as 
if polished.. Forsyth did wonders with this preparation, and 
evured with it almost all external affections of plants without 
any further trouble. It does not keep well, and therefore 
only as much “of at: must “be prepated, ‘as’is wanted for the 
time, or, if/it%is’'to be kept for some’ time, it ought to be 
moistened with utine. It should further only be applied dur- 
ine dry weather, on purpose to cover the wound with new 
bark. Rafn asserts, he had experienced the same good effects 
from a mixture of pounded coal and potatoes, or some other 
soft subtance, and even prefers this to Forsyth’s mixture. 
dry. 
