HISTORY OF BOTANY. 819 



cultivation of plants. Bossuet of Geneva proved by experi- 

 ments that the vascular system of plants is tubular and tran- 

 sparent; and that leaves perform the office of respiration. 



Grew of England ascertained the existence of the cambium, 

 and Duhamel afterwards proved that it was distinct from the 

 sap and proper juices. The latter opposed the idea, till then 

 entertained, that earth and water were the only food of plants ; 

 he proved that the various solids and fluids diffused in the soil 

 and atmosphere, are all important to vegetation. 



The observations of Priestly, Saussure, and others, aided 

 by the discoveries made in pneumatic chemistry, of the exis- 

 tence of oxygen, hydrogen, and carbonic acid gases, formed a 

 new era in the history of vegetable physiology. It was proved 

 that vegetables do ultimately consist of oxygen, hydrogen, and 

 carbon, and sometimes of a small quantity of nitrogen, com- 

 bined with mineral salts, and often some silex, sulphur, and 

 iron, which seem important to vegetable life. These elemen- 

 tary substances were found to be diffused through air and wa- 

 ter, and the animal and vegetable substances which the latter 

 holds in solution ; the green parts of vegetables were observed 

 to exhale oxygen in the light, and carbonic acid gas in the 

 dark ; and the carbon left by the decomposition ofthe carbonic 

 acid, was shown to be incorporated into the vegetable sub- 

 stance, giving to the wood its strength and hardness. 



The only naturalist who can bear any comparison with Lin- 

 naeus, is Bernard de Jussieu. He was remarkable for the ex- 

 tent of his knowledge, the penetration of his genius, and the 

 solidity of his judgment. He is said to have been unambitious. 

 The love of truth and science were with him sufficient excite- 

 ments to the most severe labour. " Many of our contempora- 

 ries," says Mirbel, " knew this sage ; they say that never have 

 they seen so much knowledge combined with so high a degree 

 of candour and modesty." To this botanist we are indebted 

 for the natural method of classification, with which you have 

 been made acquainted.* 



Jussieu proposed a method of classing plants according to 

 certain distinctions in the seed, which were found to be univer- 

 sal ; this method was perfected and published by his nephew, 

 Antoinc- Laurent de Jussieu, and is now universally received 

 as the best mode of natural classification which has yet been 

 discovered. We call this method natural, because it aims to 

 bring into groups such genera of plants as resemble each other 

 in medicinal and other properties, while the system of Linnreus 



* See Parts I. and III. 



Grew and Duhamel Priestly, &c. Character of Jossieu. 



