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CHAPTER XVI.
OF THE FUNCTIONS OF LEAVES.
The knowledge of the functions of leaves, and their real use with regard to the plant, is a curious branch of vegetable physiology, which made but a slow progress long after the nature of many other parts had been deeply scrutinized and thoroughly explained.
Caesalpinus (De Plantis, p. 6.) thought leaves merely a clothing, or a protection against cold and heat. He conceived that the rays of the sun, being moderated in passing through them, were prevented from acting too violently on the fruit and young buds. "Accordingly," says he, "many trees lose their leaves in autumn, when their fruits are perfected, and their buds hardened, while such as retain the fruit long, keep also their leaves; even till a new
