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 publication in 1804. His later contributions to the knowledge of some important questions in vegetable physiology will be mentioned further on. A comparison of the contents of the 'Recherches chimiques' with what was known of the chemistry 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 18th century had proved still more fruitful, if possible, as regards the theory of nutrition than the latter years of the 17th; 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 representatives of botany, as we shall see in the following section. It should be mentioned however that one of these misconceptions, 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 observation 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
