Page:An introduction to physiological and systematical botany (1st edition).djvu/93

 Rh upward and downward from a wound, at least proportionably to the quantity of stem or branch in either direction to supply it. Some authors have asserted that in the heat of the day it flows most from the lower part of a wound, and in the cool of the evening from the upper: hence they concluded it was ascending during the first period, and descending in the latter. If the fact be true, some other solution must be sought; nor would it be difficult to invent a theory upon this subject: but we rather prefer the investigation of truth on more solid foundations.

This great motion, called the flowing, of the sap, which is to be detected principally in the spring, and slightly in the autumn, is therefore totally distinct from that constant propulsion of it going on in every growing plant, about which so much has been said in the preceding chapter, and which is proved by taking an entire herb of any kind that has been gathered and suffered to begin to fade, and immersing its root in water. By absorption through the sap-vessels it presently revives, for those vessels require a constant supply from the root.