68 OF THE SAP, AND INSENSIBLE PERSPIRATION. 



and proves, for the most part, a clear watery 

 liquor like the sap, and subject to similar 

 chemical changes. It is observed to be uni- 

 form in all plants, or nearly so, as well as the 

 sap, except where odorous secretions transude 

 along with it. Still there must be a very es- 

 sential difference between the original sap of 

 any plant and its perspiration, the latter no 

 longer retaining the rudiments of those fine 

 secretions which are elaborated from the for- 

 mer; but that difference eludes our senses as 

 well as our chemistry. The perspiration of 

 some plants is prodigiously great. The large 

 Annual Sunflower, Helianthus annum, Ger- 

 arde TLmac. 751. f. 1, according to Dr. Hales, 

 perspires about 17 times as fast as the ordi- 

 nary insensible perspiration of the human skim 

 But of all plants upon record I think the Cor- 

 nelian Cherry, Cornus mascula, FL Grcec. 

 t. 151, is most excessive in this respect. 

 The quantity of fluid which evaporates from 

 its leaves in the course of 24 hours, is said to 

 be nearly equal to twice the weight of the 

 whole shrub. Du Hamel Phys. des Arbres, 

 *. 1. 145. 



