Abstract
IN NATURE (vol. viii., p. 245) Mr. Thiselton Dyer, in answer to a correspondent, says that he knows of no explanation? of the purpose or origin of the nectariferous glands on the back of the leaf of the cherry laurel. Mr. Darwin (“Origin of Species,” sixth edition, p. 73) says: “Certain plants excrete sweet juice, apparently for the sake of eliminating something injurious from the sap; this is effected, for instance, by glands at the base of the stipules in some Leguminosæ, and at the backs of the leaves of the common laurel. This juice, though small in quantity, is greedily sought by insects; but their visits do not in any way benefit the plant.” Glands cannot be considered very complex modifications of cellular tissue. They exist on all parts of plants, and contain a great variety of secretions. Mr. Darwin and others have shown that they perform the varied functions of secreting nectar to attract insects to flowers, of secreting odorous matter for the same purpose, of absorbing ammonia from rain-water and the products of decomposed or digested animal or vegetable matter, and of secreting acids capable of digesting solids. The existence of free acids in the plant would be injurious to it, so that their excretion would be beneficial to it apart from any digestive function which they may in some cases perform. The glands of the laurel are so far unspecialised that they are by no means constant in number or size. As their attracting insects is of no service to the plant, the nectar must be said to be excreted ; but, being what Sachs has termed (p. 629) a “secondary product of metastasis,” it should be looked upon rather as a physiologically accidental excretion than as positively injurious, as a substance which, having ceased to take part in the processes of growth, has not acquired an indirect function as has the nectar of flowers. To account for the position of the glands it may be suggested that, as in other evergreens, the leaves of the laurel are “reservoirs of reserve material” in which metastasis, including the separation of the “formative materials” from the “secondary products,” mainly takes place (Sachs, p. 627).
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BOULGER, G. Glands of the Cherry Laurel. Nature 13, 107 (1875). https://doi.org/10.1038/013107a0
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DOI: https://doi.org/10.1038/013107a0
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