The Conclufion. 37^ 



the quantity they perfpire fo confiderable, 

 that it has always been one of the greateft 

 difficulties in the ordering of a Green-houfe 

 to let in frefli air enough without expofing 

 the plants to too much cold. For fince the 

 perfpiration of trees will not be free and 

 kindly in a clofe damp air, the fap will be 

 apt to ftagnate, which will make the plants 

 grow moldy, or they will be fickly, by im- 

 bibing fuch damp rancid vapours 5 for by 

 Mr. Millers curious obfervations on the 

 perfpiration of the Plantain tree of the 

 Weft-Indies, and of the Alve under Experi- 

 ment 5, plants will often imbibe moifture in 

 the night as well in ftoves as common Green- 

 houfes without fire 5 it is certainly of as great 

 importance to the life of the plants to dis- 

 charge that infefted 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 onlypafs ia little 

 ftreams: The like contrivance would pro^ 



bably 



