DISEASES OF PLANTS. S41 
done sometimes in spring, particularly with the mul- 
berry-tree for the silkworm, should be avoided, or 
at least be done with moderation and caution. . 
Insects which are noxious to plants, should be 
accurately known, and their way of propagation 
understood, to obviate all the bad effects: they pro- 
duce, and to stop their great mcrease. 
Change of place 1s the only means to ea the 
noxious influence of acrid fumes, of great manu- 
factures and iron-works and the like, as s well as of 
dust. 
In very long continued dry weather, careful wa- 
tering is highly requisite. - abe 
The falling, off of the leaves in autumn is quite 
consistent with nature, and of no bad consequence — 
whatever, except perhaps when the leaves are drop- 
ping off too soon, on account of early frosts, which 
however will only affect very tender and foreign 
plants, of which care should be taken. 
Haemorrhagia, or the great loss of sap, is of a 
twofold kind, either eae by wounds, or spon- 
taneously. ‘Vhe species of birch and AE are very 
apt to lose a great deal of sap when wounded, which, 
when not Uonpede may kill the tree. 
Spontaneous haemorrhagy arises either from acri- 
mony of the chyle, or from too great an increase of 
the sap. When. the first is the cause of it, no re- 
medies are of any avail, as the plant soon dies, and 
its vessels become corroded. Spontaneous haemorr- 
hagy, from superabundance of sap, is either eum- 
ig mous, 
