ASCENT OF SAP 69 



and the root as the absorbing organ. Finally, Senebier 

 flatly contradicts Ingen-Housz in his views on gaseous 

 exchange in darkness — " Non," he says, " les plantes ne 

 produisent point de Tair fixe quand ellesne fermentent 

 pas." 



I cannot see on what grounds Pfeffer bases his state- 

 ment (in his Plant Physiology) that Senebier " established 

 the fact that organic substance is produced from carbonic 

 acid gas and water, while oxygen is excreted." Senebier 

 certainly did not " make it clear that the exhalation of 

 oxygen was accompanied by a corresponding decomposi- 

 tion of carbon dioxide," although Pfeffer asserts that this 

 discovery was " reserved for Senebier." On the contrary, 

 I can find no evidence that leads me to beUeve that, 

 as Hansen, a later historian of the subject, puts it, Senebier 

 was either the discoverer or even the co-discoverer of 

 carbon assimilation. 



I have passed over the names of several men who figured 

 in the history of plant physiology during the eighteenth 

 century but previous to the days of Ingen-Housz and 

 Senebier. In a sketch so brief as that I am giving you 

 I should not be justified in devoting more than a sentence 

 or two to their achievements. One of these investigators 

 was De la Baisse, who wrote about the year 1735. He 

 attempted to follow the path of ascent of sap by watering 

 the plant with coloured fluids or by placing cut branches 

 in them. Another worthy, called Reichel, also used 

 coloured fluids and identified these in the lumina of the 

 vessels and held, therefore, that vessels carry sap and 

 not air, " an unfounded notion," according to Sachs, 

 and one which Sachs himself attempted to disprove 150 

 years afterwards, but without success. 



Yet another contribution — if contribution it may be 

 called — came from the pen of Charles Bonnet, whose 

 pretentious work on the functions of leaves appeared 

 in 1754. The thesis he sets out to prove is one he adopted 

 as a " sensible suggestion " from the mathematician 



