Diurnal Potentials in the Maple Tree.
Harold Saxton Burr · PubMed · 1945
The existence of recurring phenomena in both plant and animal life is a matter of common observation. Many of these have been critically studied and something, at least, is known about the mechanism involved. In general, the recurrent rise and fall in activity has been associated with metabolic and growth phenomena in many plants. MacDougal5 reports the result of an extensive study of growth in trees as recorded on the dendograph, an instrument of his design. He called attention to the fact that growth in the tree is in part an increase in the bulk of the protoplasm in the cells of the cambium resulting in an increased diameter of the trunk and in part an increase in length due to hyperplasia in the growing points. At least a part of the increased bulk of the protoplasm is associated with water metabolism. Hence, all size measurements in trees, at least, are modified by the availability of water. Nevertheless, he was able to show that so long as water was available the majority of the trees examined showed a diurnal rise and fall in diameter. In general, the maximum occurs shortly after sunrise, and the minimum shortly after noon. However, this variation is of relatively short duration, lasting for only a few months, and is dependent in large part on climactic circumstances. It is clear enough from his experiments that only a part of the measurable growth can be attributed to cell multiplication. Apparently in the tree active mitosis is dependent in part upon the availability of water and of chemicals in solution, but it is unlikely that the entire variation in the measurements is dependent upon hydration phenomena. At least a part of the rhythm must be due to periodic increases in the numbers of cells. It is well known in the animal kingdom that mitosis is not a continuous process ibut is rather a periodic phenomenon. Witness the bursts of cell division in the developing salamander egg, so beautifully shown in Dr. L. S. Stone's film. The forces which! initiate and control those recurrent bursts of mitotic activity are entirely unknown, but there are a number of well-authenticated