282 The Physiology of Plants Book in 



ducted experiments which led him to trace a connexion 

 between the stomata and gaseous interchange. Though 

 these opinions had their origin more in connexion with 

 respiration than with the appropriation of carbon dioxide, 

 they are noteworthy in that they gave a certain starting- 

 point for the controversy we are about to discuss, and 

 that they militate against what became for a considerable 

 time the accepted view of the mechanism of gaseous 

 absorption. 



The view that the open stomata afford the path for the 

 gaseous interchanges, was put forward in a somewhat 

 tentative fashion by Sachs in 1865 in his Experimental- 

 physiologie. In his Lehrbuch he spoke more decidedly to 

 the same effect, and in the Vorlesungen, in 1882, he declared 

 the admission of gases to the interior of the plant to be 

 one of the functions of the stomata. Sachs, however, did 

 not limit this absorption to these organs, for he spoke in 

 the Lehrbuch of diffusion of gases through the cuticle as 

 a certain medium of interchange. 



The cuticular hypothesis owed its origin to Boussingault, 

 who was occupied with the problem from 1861 to 1867. 

 At the outset of his researches he re-examined and re-stated 

 with greater exactness De Saussure's view of the quanti- 

 tative relations between the two gases concerned, a very 

 important factor in the discussion of the subsequent changes. 

 The experiments on which he based his theory were per- 

 formed with leaves of Nerium Oleander, which bear stomata 

 only on their lower surfaces. Taking two precisely similar 

 leaves of this plant, he coated the upper side of one and 

 the lower side of the other with lard, which he took to be 

 impermeable to the passage of carbon dioxide. The 

 leaves so prepared were then exposed to bright diffused 

 light for eight hours, in glass tubes containing air to which 

 a known quantity of carbon dioxide had been added. He 

 found that the leaf with the stomata occluded decom- 



