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[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.
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