CHAP, ii.] of Plants. De Saussure. 505 



where questions of nutrition turned on the movement of the 

 sap, was the backward condition of the study of the inner 

 structure of plants, as described in the second book. For 

 instance, the question of the descending sap was complicated 

 in the strangest way by Du Petit-Thouars's theory of bud-roots 

 that descend between the bark and the wood ; Reichel's un- 

 founded idea of the rising of the sap in the tubes of the wood 

 was generally accepted, and a still worse error was maintained 

 by some, that the intercellular spaces of the parenchyma are 

 true sap-conveying organs. In 1812 Moldenhawer had to in- 

 sist, but without producing any general conviction, that the 

 vessels of the wood contain air, and Treviranus in 1821 that 

 the stomata serve for the entrance and exit of air. We need 

 not notice here what nature-philosophers like Kieser said about 

 nutrition and the movement of the sap ; but even those who 

 were far from adopting the extravagancies of this school were 

 incapable of either making use of or carrying on the labours of 

 Ingen-Houss, Senebier, and de Saussure. We may adduce in 

 proof of this statement the remarks of Link on the function of 

 leaves in his 'Grundlehren der Anatomie und Physiologie,' 1807. 

 He says at p. 202 that their function is according to Hales 

 transpiration, according to Bonnet absorption, according to 

 Bjerkander the exudation and secretion of a variety of fluids, 

 according to Hedwig the storing up of juices, and inasmuch as 

 leaves increase the green surfaces of plants, bear stomata and 

 hairs, and hold a quantity of juices in their abundant paren- 

 chyma, we may ascribe all these functions, but none of them 

 exclusively, to leaves ; the only thing peculiar to them is that 

 they convey elaborated juices to the young parts. Their great 

 work, the decomposition of carbon dioxide, he does not men- 

 tion. But this neglect of the doctrines of Ingen-Houss, Sene- 

 bier, and de Saussure was common, especially in Germany ; it 

 is seen in the efforts made to prove once more the existence of 

 a descending sap in the rind, just as it had been proved in the 

 two previous centuries, by the result of removing a ring of bark 



