Concluding remarks on the circumnutation of leaves.

The circumnutating movements of young leaves in 33 genera, belonging to 25 families, widely distributed

* ’Ueber die Bewegungen der Faden der Spirogyra princeps:  Jahreshefte des Vereins für vaterländische Naturkunde in Württemberg,’ 1874, p. 211.

** Zukal also remarks (as quoted in ‘Journal R. Microscop.  Soc.,’ 1880, vol. iii. p. 320) that the movements of Spirulina, a member of the Oscillatorieae, are closely analogous “to the well-known rotation of growing shoots and tendrils.” [page 260]

amongst ordinary and gymnospermous Dicotyledons and amongst Monocotyledons, together with several Cryptogams, have now been described.  It would, therefore, not be rash to assume that the growing leaves of all plants circumnutate, as we have seen reason to conclude is the case with cotyledons.  The seat of movement generally lies in the petiole, but sometimes both in the petiole and blade, or in the blade alone.  The extent of the movement differed much in different plants; but the distance passed over was never great, except with Pistia, which ought perhaps to have been included amongst sleeping plants.  The angular movement of the leaves was only occasionally measured; it commonly varied from only 2o (and probably even less in some instances) to about 10o; but it amounted to 23o in the common bean.  The movement is chiefly in a vertical plane, but as the ascending and descending lines never coincided, there was always some lateral movement, and thus irregular ellipses were formed.  The movement, therefore, deserves to be called one of circumnutation; for all circumnutating organs tend to describe ellipses,—­that is, growth on one side is succeeded by growth on nearly but not quite the opposite side.  The ellipses, or the zigzag lines representing drawn-out ellipses, are generally very narrow; yet with the Camellia, their minor axes were half as long, and with the Eucalyptus more than half as long as their major axes.  In the case of Cissus, parts of the figure more nearly represented circles than ellipses.  The amount of lateral movement is therefore sometimes considerable.  Moreover, the longer axes of the successively formed ellipses (as with the Bean, Cissus, and Sea-kale), and in several instances the zigzag lines representing ellipses, were extended in very different directions during the same day or on [page 261] the next day.  The course followed was curvilinear or straight, or slightly or strongly zigzag, and little loops or triangles were often formed.  A single large irregular ellipse may be described on one day, and two smaller ones by the same plant on the next day.  With Drosera two, and with Lupinus, Eucalyptus and Pancratium, several were formed each day.