Page:An introduction to physiological and systematical botany (1st edition).djvu/114

 84 in professedly chemical works, is carried to a greater length than I have thought necessary in a physiological one. See Thomson's Chemistry, v. 4, and Willdenow's Principles of Botany, 229. We must ever keep in mind, as we explore it, that our anatomical instruments are not more inadequate to dissect the organs of a scarcely distinguishable insect, than our experiments are to investigate the fine chemistry of Nature, over which the living principle presides.

Before we take leave of the secreted fluids of vegetables, a few more remarks upon their direct utility to the plants themselves may not be superfluous. Malpighi first suggested that these secretions might nourish the plant, and our latest inquiries confirm the suggestion. Du Hamel compares them to the blood of animals, and so does Darwin. But the analogy seems more plain between the sap, as being nearly uniform in all plants, and the animal blood, as in that particular they accord, while the secreted fluids are so very various. Mr. Knight's theory confirms this analogy, at the same time that it establishes the opinion of Malpighi. The sap