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

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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$there are also other contrivances of a very different nature which have the sole purpose of transferring the pollen of hermaphrodite flowers, by the help of insects, to the stigma of another flower of the same or of a different plant. In most Orchidese, Asclepiadeas, Viola, &c., the reproductive organs of each individual flower are developed at the same time, but at the time of maturity mechanical contrivances exist which prevent the pollen falling on the stigma of the same flower; it must be carried by insects to other flowers. In other cases, as Hildebrand has shown in the case of Corydalis cava \ the pollen does actually fall on the stigma of the same flower, but is there impotent, having the power of fertilising only when it falls on the stigma of a different flower, and only perfectly when carried to the flower of a different individual of the same species. Such a plant is therefore only morphologically hermaphrodite, but is physiologically dioecious. J. Scott states that Oncidium michrochilum exhibits the same phenomena, the pollen not being potent on the stigma of the same flower, while cross-pollination ensures fertilisation1 2; the pollen and stigma are therefore without function except to the stigma and pollen of a different flower. Similar phe- nomena have been described by Gartner in the case of Lobelia fulgens and Verbascum nigrum, and in species of Begonia by Fritz Muller3 *. No less remarkable is another contrivance for the mutual fertilisation of different individuals of plants with hermaphrodite flowers,—Dimorphism4 (or Heterostylism), consisting in a difference between different individuals of the same species with reference to their reproductive organs. In one individual the flowers all have a long style and short filaments, while in another individual all the flowers have a short style and long filaments, as in Linum perenne, Primula sinensis, and other species of Primula. It sometimes happens also, as in Lythrum Salicaria and many species of Oxalis5, that the reproductive organs in the flowers of different specimens of the same species exhibit three different relative lengths (Trimorphism), there being an intermediate length of style between the long-styled and the short-styled forms. In these cases of dimorphism and trimorphism Darwin and Hildebrand have shown that fertilisation is possible only (in the case of Linum perettne) or at least has the best result when the pollen of the long-styled flower is carried to the short-styled stigma of another plant,and vice versa6. Where there are three different lengths of style, fer- tilisation succeeds best when the pollen is carried to the stigma which stands at the same height in another flower as the anthers from which the pollen came. It will be seen that this is but an expansion of the same rule. 1 [Ueber die Befruchtung von Corydalis cava, Jahrb. fur wiss. Bot. 1866.] 2 According to Fritz Muller (Bot. Zeit. 1868, p. 114), in some species of Oncidium the pollen- masses and stigmas of the same individual have a positively poisonous effect on one another. 3 Fritz Muller, Bot. Zeit. 1864, p.629. * [Darwin, On the Two Forms, or Dimorphic Condition, in the Species of Primula, Journ. Proc. Linn. Soc. Bot. 1862, p. 77; ditto, On the Existence of Two Forms, &c. of the Genus Linum, ibid , 1863, p- 69 ; ditto. On Trimorphism in Lythrum Salicaria, ibid. 1864, p. 169; ditto. On the Character and Hybrid-like Nature of the Offspring from the Illegitimate Unions of Dimorphic and Trimorphic Plants, Journ. Lin. Soc. 1868, p. 393.—Ed.] 5 Hildebrand, Bot. Zeit. 1871, Nos. 25, 26. 6 [Darwin has given the name of legitimate to the union of two distinct forms, illegitimate to the impiegnation of long- or short-styled plants by their own form pollen.—Ed.]$