AND INSENSIBLE PERSPIRATION, 67 



ed by the warm days- of autumn, when the 

 nights are cold, than in mueh hotter weather 

 in summer, and this is surely from the same 

 cause as the autumnal flowing of the vegetable 

 sap. 



The sap, or lymph, of most plants when 

 collected in the spring as abovementioned, 

 appears to the sight and taste little else than 

 water, but it soon undergoes fermentation 

 and putrefaction. Even that of the vine is 

 scarcely acid, though it can hardly be ob- 

 tained without some of the secreted juices, 

 which in that plant are extremely acid and 

 astringent. The sap of the sugar maple, 

 Acer saccharinum, has no taste, though ac- 

 cording to Du Hamel every 200lb. of it will 

 afford 101b. of sugar. Probably, as he re- 

 marks, it is not collected without an admix- 

 ture of secreted fluids. 



As soon as the leaves expand, insensible 

 perspiration takes place very copiously, chief- 

 ly from those organs, but also in some degree 

 from the bark of the young stem or branches. 

 The liquor perspired becomes sensible to us 

 by being collected from a branch introduced 

 into any sufficiently capacious glass vessel, 



F2 



