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
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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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    These general observations show that the sexual differentiation stands, in the various classes of plants, in a very different relationship to the morphological differentiation manifested in the alternation of generations. Hence it arises that the product of the fertilised oosphere has from a morphological point of view a very different value in different groups of plants. In the Conjugate it is a zygospore from which generations of cells are subsequently developed similar to the mother-cells of the zygospore; in Vaucheria, CEdogonium, and Coleochaete it is an oospore from which an asexual gener- ation developes, proceeding from it in different ways; in the Muscineae the asexual generation constitutes the so-called fruit of Mosses; in Vascular Cryptogams and Pha- nerogams it is the plant furnished with leaves and rooting in the soil. The process of development brought about by fertilisation or the union of the repro- ductive cells'is usually not confined to the resulting embryo, but shows itself also in a variety of changes in the mother-plant itself. In Coleochaete the oospore becomes in- vested with a cortical layer; in Characeae the enveloping tubes of the nucule grow after fertilisation, their coils increase in number, and their membranes become lignified on the inside; in the Hepaticae a variety of envelopes arise from the mother-plant; in the Mosses the vaginule and in all Muscineae the calyptra becomes developed ; the tissue of the prothallium which surrounds the growing embryo of Ferns grows at first rapidly along with it; in Phanerogams the entire development of the seed and fruit depends on the changes caused in the mother-plant by the fertilisation of the embryonic vesicles. The two most remarkable cases occur in Florideae and Ascomycetes on the one hand, and in Orchideae on the other hand. In the former fertilisation does not in general directly cause the formation of an embryo, but brings about processes of growth in the mother-plant, in consequence of which the cystocarp is produced in Florideae and the fruit in Ascomycetes. In the Orchideae the action of the pollen-tube is visible on the mother-plant even before fertilisation; Hildebrand has shown (Bot. Zeit. 1863^.341) that in all Orchids which he examined the ovules were not in a condition to be fertilised at the time of pollination; and in some (as Dendrobium while) they have not even begun to be formed; it is only during the growth of the pollen-tubes through the tissue of the stigma and style that the ovules become so far developed that fertilisation can at length be effected. In the Orchideae the formation of the female cell is therefore a result of pollination; it is determined by the action of the male pollen-tube on the tissue of the mother-plant1. When the embryo is developed within the mother-plant, as in the Muscineae and Vascular Cryptogams, it withdraws its food-material from the plant; this being con- nected in the Vascular Cryptogams with complete exhaustion and the dying off of the prothallium. In Phanerogams not only does the embryo usually acquire a considerable development, even within the fruit, but a great quantity of the products of assimilation is also withdrawn from the plant by the accumulation of reserve-material in the seed and by the development of the fruit; in many cases the plant itself is also completely exhausted, all its disposable formative substances are given up to the seed and the fruit, and it dies off (monocarpous plants). It is clear that all these changes, and the various movements of materials in the mother-plant connected with them are results of fertilisation, results of immense importance caused by the union of microscopic cells, imponderable by the best balance. Achlya polyandra; the only difference between the parthenogenetic germ-cells and those produced by the ordinary process of fertilisation being that the former remain dormant for a longer period. (See Braun, Abhand. der Berlin. Akad. 1856; and Pringsheim, Jahrb. fur wiss. Bot. vol. IX, p. 191). —Ed.] 1 [For a summary of the instances in which pollen appears to have influenced the fruit of the mother-plant, see C. J. Maximowicz, Journ. Roy. Plort. Soc. new series, vol. III. p. 161; and Darwin, Animals and Plants under Domestication, vol. I, p. 397.—Ed.]