$40 PRINCIPLES OF BOTANY. 
produce an increase of the sap, should be trans- 
planted into a poorer soil. ‘To defend them against 
frost, plants should be covered with straw. . 
 Accleft occasioned by the last often degenerates 
into a chilblain, (pernio), from which afterwards, 
especially in oaks, a blackish sharp liquor exudes, 
which at last produces exulceration, (§ 327). 
‘ § 308. 
Defilintic notha, when the leaves fall not at the 
proper period, but much earlier. The injuries of 
man, insects, acrid pungent fumes, dust, and con- 
stant dry weather, have this effect. 
In whatever way it may happen, all depends on 
the nature of the plant affected with it, and on the 
season of the year in which it happens. If it be a 
fast growing tree, and the injury happens before 
August, the tree may, if taken good care of, easily 
get leaves again, only it will have but a few and 
small leaves for the present season. But if the 
leaves fall, after that period, and cool weather comes 
on earlier than usual, or if it happens at a much 
later season, the plant may be unwell for several . 
years, before a complete recovery takes place. If, 
on the contrary, it happens late in autumn, just be- 
fore the natural fall of the leaves, then it has no 
bad consequences, except the plants be natives of a 
warmer climate, and the branches, which have ap- 
peared already, be not yet hard enough, in which 
case they will lose those branches, and perhaps 
some of the older ones, by the invasion of cold. 
‘To deprive trees oe their leaves purposely, which is 
done 
