(189.) Diffusion of proper Juice. — The crude sap having been subjected to the action of the atmosphere and the carbonic acid decomposed, the result is termed the “ proper juice” or elaborated sap of the plant. This liquid has now to find its way back again into the system for the purpose of nourishing and developing the various parts. There are three distinct kinds of movement to which the proper juices of plants are subjected. The first of these is its descent and transfusion; the second is a very singular rotation of the juices contained in the vesicles and short tubes of some plants; and the third is a sort of actual though local circulation more nearly resembling the circulation of blood in animals. We propose to describe each of these under the present period, though certainly they can hardly be all considered as subordinate processes of the same function.

(190.) Descent of Sap. — When a ring of bark is removed from a stem or branch of a dicotyledonous plant a tumour is formed at the upper edge of the ring, which indicates a stoppage to have taken place in the descent of the elaborated sap. This stoppage by causing an excess of nutriment to accumulate above the ring, operates in improving the size and quality of fruits, and will even occasion a tree to flower and produce fruit when it would otherwise have developed nothing but leaves.