Page:An introduction to physiological and systematical botany (1st edition).djvu/116

 86 proportion of mucilage at the end of Autumn than in the early spring. If these substances do not nourish the plant, they seem to be of no use to it, whatever secondary purposes they may answer in the schemes of Providence. The direct end, with respect to the plant, of the finer secreted fluids of its fruit can very well be perceived, as tempting the appetite of animals, and occasioning, through their means, the dispersion of the seeds; and the perfume of flowers may attract insects, and so promote the fertilization of the seed, as will be explained hereafter.

After what has been said we need not waste much time in considering the hypothesis, advanced by some philosophers, that the sap-vessels are veins and the returning vessels arteries. This is so far correct, that, as the chyle prepared by the digestive organs, poured into the veins and mixed with the blood is, through the medium of the heart, sent into the lungs to be acted upon by the air; so the nutrimental juices of plants, taken up from the earth, which has been called their stomach, are carried by the sap-vessels into the leaves, for similar purposes already