But they were swayed by that egotistical instinct which leads man to refer everything to himself, even the very gods which he has created after his own image. The Bible teaches us that there is but one God. Alas! are there not as many gods as there are men? Does not each of us create a deity in accordance with his own inclinations, his mode of thought, his degree of mental culture, the sphere of his ideas? Is the God of a tolerant philosopher identical with that of a bigoted fanatic? It is not so much due to a deceitful appearance, an optical illusion, as to a kind of innate infatuation, that the human race have come to consider the planet they inhabit as the centre of the universe.
Causes of the Circulation of the Sap.
Let us return to the sap, the life-blood of vegetation.
How is it that its movement does not recommence at the same time in all plants? Why are some clothed with leaves when the others are scarcely budding? Wherefore, in certain genera, do the flowers appear before the leaves?
Some authorities assert,—but facts show it to be a purely gratuitous supposition,—that the flower, which, with the fruit, seems to be the goal or object of vegetation, demands a greater activity on the part of the sap. But, in truth, many trees and shrubs, such as the poplar, the willow, and the hazel, flourish at an epoch when the sap is barely aroused from its protracted lethargy.
These are questions which have still to be answered.
But upon yet another question we may dwell at some detail. What is the cause of the circulation of the sap?
To the best of our knowledge, this important problem has never been propounded as it should have been. And for this reason: all observers who have taken up its consideration have had in view only the rising sap, and the cause of its rising. Evidently this is but a part of the problem. The ascending sap, after undergoing an important modification in the leaves, becomes the descending sap; just as the venous blood is transformed, on coming into contact with the air in the lungs, into arterial blood. It is this alternative movement of going and coming which constitutes the circulation both of the sap and the blood, and which ceases completely only with the life of the plant or the animal. We must, therefore, bear in mind,—which has not been hitherto done,—these two opposite, yet indissolubly connected, movements, before we can approach with advantage the solution of the proposed question.[40]