368 HISTORY OF THE ROYAL BOTANIC GARDEN. 
with the thermometer out of doors 15 or 16 deg. below the freezing 
point. Such treatment is bad for all plants, but more particularly 
for heaths. If we were certain that the thermometer during the 
night would not sink more than 1o or 12 deg. below freezing out of 
— no artificial heat whatever would be necessary in the heath- 
ouse. 
It is an excellent practice in ae a ms cpa, and even frosty 
weather, if much damp is in the hous throw in a little heat 
during the day, but this aad never os Pose unless the weather is 
such that plenty of air can be given to the house at the same time, 
nor even when frost is in the house; and the heat should always be 
stopped before the air is taken off. This, however, is unnecessary 
unless the plants appear to suffer from damp. Very little water 
the homens falls more than 8 deg. below freezing ; a 
then it is advisable to ates: some additional pase & The woolly- 
leaved kinds, such as Erica Masson nt, gemmifiora, brace ) 
oo &e., are very liable to suffer in such situations. It is, 
. below 
be mu 
ho many others will require ro or 12 deg. below freezing to 
the same effect. A list of those which I have repeatedly 
