The Enigma Of Sap

Ever since the law of gravity decreed that water must not run uphill, trees have played the role of recreant. In tree trunks the sap rises seemingly in direct defiance of this edict. And since science insists on finding some rational explanation when well-defined laws of Nature appear to be violated, she has persistently tried to explain the hidden forces that cause the upward flow of this vital fluid in living plants. But in spite of patient search and research there exists still in Nature many a shadowy borderland country only dimly lighted by our actual knowledge of material things and only scantily defined by our cleverest theories. The forces that lie imprisoned within the atom; the problem of the ultimate nature of matter, the age-old question as to the origin of life itself—all these belong somewhere in that unexplored, uncharted country to which science has found only indifferent guides.

It is well to admit that such enigmas still challenge our most careful investigations, especially when attempting to discuss what the great Darwin himself called "that most nebulous of subjects." So familiar has this fact of the rise of the sap stream become in our daily living that only those who have tried scientifically to explain its processes have come to realize its baffling complexities. Popular misconceptions on the subject are numerous. To-day, no less than twenty years ago, your practical woodsman speaks of the sap being "up" in summer and "down" in winter, although in truth there is less sap in trees during the warm months than at any other time.

In the case of “up” you have one refutation of the old saying, that what goes up is sure to come down; for a great deal of sap that goes up never returns to earth. Here, of course, I am using the word "sap" rather loosely, as '(generally done, to mean any moisture that a tree may obtain. As a matter of fact the fluid that ascends is practically the same as the water that lies in felt soil and flows in the streams, and only when it has been subjected to the mysterious chemical changes that take place in those green laboratories, the leaves, may srtictly be known as sap.

After these changes it starts on its downward course laden with food material —starches and sugars, cell builders and wood producers. And long before it arrives at the base of the tree, whence it started, most of this material has been deposited and most of the water itself has been evaporated. So the original fluid that goes up the tree never comes down again. And when in the autumn the leaves fall and the sap ceases to circulate it is held motionless in the trunk of the tree and in the branches, there to remain throughout the winter, waiting for the coming of the leaves to bring it into action again.

By: davidbunch

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