Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer.

Date:
1875
Catalogue details

Licence: Public Domain Mark

Credit: Text-book of botany : morphological and physiological / by Julius Sachs ; translated and annotated by Alfred W. Bennett ; assisted by W.T. Thiselton Dyer. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    in the hop, dahlia, and bryony. In bulbs again the reserve accumulates in the leaves (bulb-scales) which surround the bud that developes into the new plant. The reserve often collects in cataphyllary leaves of peculiar development; in Allium Cepa in the lower part of the leaf-sheaths, which persist through the winter, while the upper parts of the leaves die off. We have already in the last chapter spoken of the immense variety of the contrivances which have for their object the partial or entire prevention of the self-fertilisation of plants, in order to produce a stronger and more numerous off- spring by the sexual union of different individuals; and only a few examples need now be mentioned. Since the form, size, colour, position and movements of the parts of the flower are almost invariably adapted to facilitate the conveyance of pollen from one flower to another, generally by insects, and often even to render self-fertilisation impossible; and since a great diversity even of those forms of flowers which are constructed on the same morphological type results from this, so the properties of ripe seeds and fruits are no less adapted1 to bring about the disse- mination of the seeds. Fruits which are very similar from a morphological point of view may nevertheless assume physiological properties which are altogether different, and fruits which are very different morphologically may become extremely similar in consequence of their adaptation to the purposes of dissemination. The service rendered by insects in the fertilisation of diclinous, dichogamous, dimorphic, and many other flowers, is performed by birds in the dissemination of a number of seeds which are concealed beneath fleshy edible pericarps; in some cases, as the mistletoe, it is scarcely possible to imagine any other mode of dissemination than the eating of the berries by birds. Dry fruits or the seeds which are shed by dry fruits are often provided w'ith an apparatus adapted for transport by the wind, the morpho- logical value of w’hich is as various as possible. The wings on the seeds of species of Abies are a superficial layer of the tissue of the scale (carpel), those on the seed of Bignonia viuricata originate from the integument of the ovule; the wings of the indehiscent fruits (samarse) of Acer, Ulmus, &c., are outgrowths of the pericarp; the crown of hairs on the seed of Asclepias syriaca evidently performs a similar service; as does the pappus of many Composite which is a metamorphosed calyx. In these cases it is obvious that the wind carries the seeds or fruits; in other cases animals of considerable size perform this office involuntarily, the hooked or rough fruits becoming attached to them and afterwards falling off2. In most of these adaptations, both their purpose and the mechanical con- trivances for its attainment are easily recognised; but not unfrequently the latter require a closer examination and some reflection in order to understand them. Among many other cases of this kind one only may be mentioned here which any one can easily observe for himself. The fruit of Erodium gruinum and other Geraniaceae3 * 5 splits up into five mericarps each of which has the form of a cone with 1 It is scarcely needful to mention again that this mode of expression has only a metaphorical meaning from the stand-point here assumed, and is only used for the sake of convenience. - [A remarkable instance of this is recorded by Dr. Shaw (Journ. Linn. Soc. vol. XIV, 1874, p. 202), in the introduction into South Africa and enormously rapid distribution of a European plant, Xanthium spinosum, by the spiny achenes clinging to the wool of the Merino sheep.—Ed.] 5 See Hanstein, Sitzungsber. der niederrheinischen Ges. in Bonn, 1868.