The Conclufton. 37 ^ 
the quantity they perfpire fo confidcrable, 
that it has always been one of the greateft 
difficulties in the ordering of a Green-houfe 
to let in frefh air enough without expofing 
the plants to too much cold. For fincc the 
perfpiration of trees will not be free and 
kindly in a clofe damp air, the fap will be 
apt toftagnate, which will make the plants 
grow moldy, or they will be lickly, by im- 
bibing fuch damp rancid vapours 5 for by 
Mr. Millers curious obfervations on the 
perfpiration of the Plantain tree of the 
JVeJl- Indie Sy and of the Alve under Experi- 
ment 5, plants will often imbibe moifture in 
the night as well in ftoves as common Grccn- 
houfes without fire 5 it is certainly of as great 
importance to the life of the plants to dif- 
charge that infeded rancid air, by the ad- 
mittance of frefh, as it is to defend them from 
the extream cold of the outward air, which 
will deftroy them if let in immediately upon 
them. It feems therefore to be a very reafon- 
able method which fome ufe, viz. to cover 
fome of the inlets of their Green-houfes on 
all fides with canvafs, and in extream cold 
weather with fhutters made of reed or ftraw, 
through which the air can only pafs in little 
ftreams: The like contrivance would pro- 
bably 
