102 HISTORY OF BOTANY 



But you will recognise several old friends such as con- 

 tractility of cells and vessels, intercellular spaces as sap 

 conduits, soil as the source of some at least of the carbon 

 dioxide, the ascent of " crude sap " by day and the 

 descent of " elaborated sap " by night, the muddle 

 between reserves and excreta, not to speak of the " vital 

 energy " which was supposed in some mysterious way 

 to be associated with the contractility of young cells. 

 All these blunders and misconceptions, in a treatise on 

 vegetable physiology written a generation after the days 

 of De Saussure, make one marvel how such a pronounce- 

 ment could have emanated from the pen of a botanist 

 of the rank of De Candolle. It is indeed but a short step 

 in advance of the phantasies of the sixteenth-century 

 herbalists. 



Another physiological investigator, a countryman 

 and a contemporary of De Candolle, was Dutrochet. 

 In his Memoires, published in 1837, Dutrochet cleared 

 up quite a number of special points. He was the first to 

 emphasise the importance of osmosis in plant nutrition, 

 a subject he had studied some years previously in relation 

 to the escape of gonidia in Thallophyta. He distinguished 

 " spring bleeding," which he attributed to root pressure 

 resulting from excessive endosmosis, from the normal 

 transpiration current, which he regarded as induced by 

 the suctional power of transpiring leaves, the vis a 

 tergo and the vis a fronte of the early textbooks. He 

 also did good service in pointing out that respiration 

 in plants is identical with that in animals, and thus was 

 instrumental in destroying the old notions about diurnal 

 and nocturnal respiration. On respiration, according to 

 Dutrochet, all growth and movement were absolutely 

 dependent, and he further showed that the evolution of 

 heat, with or without an accompanying rise of tempera- 

 ture, was a necessary consequence of the chemical processes 

 taking place in all active plant organs. The recognition 

 of these chemical phenomena in plants as well as the 



