Page:An introduction to physiological and systematical botany (1st edition).djvu/98

68 and proves, for the most part, a clear watery liquor like the sap, and subject to similar chemical changes. It is observed to be uniform 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 essential 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 former; but that difference eludes our senses as well as our chemistry. The perspiration of some plants is prodigiously great. The large Annual Sunflower, Helianthus annuus, Gerarde Emac. 751. f. 1, according to Dr. Hales, perspires about 17 times as fast as the ordinary insensible perspiration of the human skin. But of all plants upon record I think the Cornelian Cherry, ''Cornus mascula, Fl. Græc. 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, v.'' 1. 145.