16. I have only one chance left now. Lindley's "Introduction to Botany." 'Sap,'--yes,--'General motion of.' II. 325. "The course which is taken by the sap, after entering a plant, is the first subject for consideration." My dear doctor, I have learned nearly whatever I know of plant structure from you, and am grateful; and that it is little, is not your fault, but mine. But this--let me say it with all sincere respect--is not what you should have told me here. You know, far better than I, that 'sap' never does enter a plant at all; but only salt, or earth and water, {49} and that the roots alone could not make it; and that, therefore, the course of it must be, in great part, the result or process of the actual making. But I will read now, patiently; for I know you will tell me much that is worth hearing, though not perhaps what I want. Yes; now that I have read Lindley's statement carefully, I find it is full of precious things; and this is what, with thinking over it, I can gather for you. 17. First, towards the end of January,--as the light enlarges, and the trees revive from their rest,--there is a general liquefaction of the blood of St. Januarius in their stems; and I suppose there is really a great deal of moisture rapidly absorbed from the earth in most cases; and that this absorption is a great help to the sun in drying the winter's damp out of it for us: then, with that strange vital power,--which scientific people are usually as afraid of naming as common people are afraid of naming Death,--the tree gives the gathered earth and water a changed existence; and to this new-born liquid an upward motion from the earth, as our blood has from the heart; for the life of the tree is out of the earth; and this upward motion has a mechanical power in pushing on the growth. "_Forced onward_ by the current of sap, the plumule ascends," (Lindley, p. 132,)--this blood of the tree having to supply, exactly as our own blood has, not only the forming powers of substance, but a continual evaporation, "approximately seventeen times more than that of the human body," while the force of motion in the sap "is {50} sometimes five times greater than that which impels the blood in the crural artery of the horse."