CHAP, ii.] of Plants. De Saussure. 503 



and fifty or sixty years were to elapse before light was thrown 

 on the questions thus raised by de Saussure. 



Such were the most important contents of de Saussure's pub 

 lication in 1804. His later contributions to the knowledge of 

 some important questions in vegetable physiology will be men- 

 tioned further on. A comparison of the contents of the 

 * Recherches chimiques ' with what was known of the che- 

 mistry of the food of plants before 1780 excites the liveliest 

 astonishment at the enormous advance made in these twenty- 

 four years. The latter years of the i8th century had proved 

 still more fruitful, if possible, as regards the theory of nutrition 

 than the latter years of the iyth; both periods have this in 

 common, that they developed an extraordinary abundance of 

 new points of view in every branch of botanical science. They 

 resemble each other also in the circumstance that they were 

 both followed by a longer period of inactivity ; the time from 

 Hales to Ingen-Houss was highly unproductive, and so also were 

 the thirty years that followed the appearance of de Saussure's 

 great work, though it must be admitted that some good work 

 was done during that period in France, while in Germany the 

 new theory was grossly misunderstood by the chief repre- 

 sentatives of botany, as we shall see in the following section. 

 It should be mentioned however that one of these misconcep- 

 tions, which was not removed till after 1860, was caused by 

 de Saussure himself. He had observed that the red leaves of 

 a variety of the garden Orache disengage oxygen from carbon 

 dioxide, as much as the green leaves of the common kind. In 

 this case he was hasty, and concluded from this single ob- 

 servation that the green colour is not an essential character of 

 the parts which decompose carbonic acid ; if he had only 

 removed the epidermis of the red leaves he would have found 

 that the inner tissue is coloured as dark green as the ordinary 

 green leaves. He who was usually so extremely careful as an 

 observer was for once negligent, and later writers, as is apt to 

 happen, fixed exactly on this one weak point, and repeatedly 



