ABSORPTION OF RAIN AND DEW BY GREEN PARTS OF PLANTS. 167 



ON THE ABSORPTION OF RAIN AND DEW BY THE 

 GREEN PARTS OF PLANTS. 



By the Rev. Prof. George Henslow, M.A., F.L.S., V.M.H. 



Lecture delivered June 23, 1908. 



1. Introduction. 



The subject of this paper was a matter of controversy for 150 years ; but 

 it is hoped that at last the question whether moisture of any kind is 

 absorbed or not by the aerial parts of plants will be set at rest for ever, 

 and answered in the affirmative. 



The many and varied experiments I have made, extending over some 

 years, have convinced me that such is the case ; and they corroborate 

 entirely the conclusions of M. Boussingault and other physiologists. 

 M. Boussingault's researches proceeded simultaneously with my own, but 

 were quite unknown to me until they appeared in the " Annales de Chimie 

 et de Physique " (March 1878) ; and, while our conclusions were identical, 

 our respective experiments really supplemented each other. 



Hales, in 1731, and Bonnet, in 1753, alike inferred, but did not 

 actually prove, that plants absorbed rain and dew. 



In 1849 Garreau proved that the cuticle, instead of entirely resisting 

 penetration by water, allowed it to pass inwards. 



De Candolle, Meyen, Treviranus and others, however, objected to 

 Bonnet's conclusions, asserting positively, but apparently without ex- 

 perimental evidence in support, that the leaves which he laid on the 

 surface of water kept fresh for lengthened periods solely because tran- 

 spiration was assumed to be arrested. Had they fixed watch-glasses on 

 the surfaces of the leaves, as I did, transpiration would have been easily 

 detected. 



Notwithstanding these objectors, a general belief in the power of 

 absorption seems to have been held until 1857, when M. Duchartre 

 performed his experiments ; and although he had himself been previously 

 of the opinion that if plants could not absorb vapour (which Boussingault 

 has proved to be the case) they could at least imbibe dew and rain, yet he 

 was led to abandon this view ; and he is responsible for the opposite one 

 having being generally held by vegetable physiologists. It should be 

 observed that practical horticulturists never abandoned the idea that 

 plants can and do absorb water by their leaves. 



As this change of view was somewhat of an obstruction to the 

 progress of vegetable physiology, and, as far as I am aware, no serious 

 attempt was made to refute Duchartre's conclusions, I propose showing 

 how experiments proved them to be erroneous. 



He commenced * his paper by objecting strongly to experimenters 



* "Recherches sur les rapports des plantes avec la rosee," Bull. de la Soc Bot. 

 de France, t. iv. p. 940 ; " Recherches experimentales sur les rapports des plantes 

 avec la rosee et les hrouillards," Ann. des Sc. Nat. 4 ,n '' ser. xv. p. 109. 



