Volume 4

The natural history of plants : their forms, growth, reproduction, and distribution / from the German of Anton Kerner von Marilaun ; translated and edited by F.W. Oliver, with the assistance of Marian Busk and Mary F. Ewart ; with about 2000 original woodcut illustrations and sixteen plates in colours.

  • Kerner von Marilaun, Anton, 1831-1898.
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: The natural history of plants : their forms, growth, reproduction, and distribution / from the German of Anton Kerner von Marilaun ; translated and edited by F.W. Oliver, with the assistance of Marian Busk and Mary F. Ewart ; with about 2000 original woodcut illustrations and sixteen plates in colours. Source: Wellcome Collection.

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    visit a flower, the anthers ai'e still full of pollen at the close of its flowering period, and being then displaced let fall their pollen upon the slightest vibration of the pendent blossom, or even when it is quite still. The pollen falls straight down and is caught by the stigma below. The process above described is only observed to take place in pendent flowers where the pollen is of floury consistency and the stamens are united into a conical cap. Flowers borne on horizontal stalks, and facing sideways, may exhibit the same phenomenon in connection with separate stamens. Only an important circumstance in this case is that some of the anthers should be exactly over the stigmas at the time of dehiscence. With a view to cross-fertilization, lateral flowers of the kind are protogynous, and have their anthers closed when the buds open; but later on the anthers dehisce, and a portion of the pollen then liberated falls out, owing to the contraction of the walls of the anthers, and besprinkles the stigma of the same flower. This method of autogamy has been observed in par- ticular in the flowers of Tofteldia and the Bog Asphodel (Narthecium). Even in upright flowers autogamy sometimes takes place in the second half of their time of flowering through a fall of pollen, and that without any change of position on the part of petals, stamens, or style. To make cross-fertilization possible, in the first instance, flowers of this kind are protogynous. Subsequently, after the dehiscence of the anthers, a portion of the crumbly pollen becomes detached, and is deposited on the stigma below. In the case of erect flowers with funnel-shaped corollas, the pollen slips down the smooth sloping wall of the funnel to the stigma, and it is not essential for the anthers to stand vertically above the stigma, since the corolla acts as a sort of conduit for the pollen. The Lilac (Syringa) is an example of the plants of this category. It is also remarkable for the fact that, though its flowers are only protogynous for a very short time, yet, for one or two days after the dehiscence of the anthers, autogamy cannot take place, because the anthers face outwai'ds. So long as the anthers are in this position the pollen cannot be transferred without extraneous aid to the corolla- tube; it is not till later on, when the anthers get covered all round with pollen, owing to the gradual shrinkage of their walls, that some of the pollen drops on to the stigma standing underneath in the tube of the funnel. Very often in erect or obliquely ascending flowers autogamy is brought about by an elongation of the filaments during the period of flowering, the result being that the anthers, which are originally lower down than the stigmas, are elevated to the same level as the latter, and are thus enabled to deposit their pollen upon them. Most of the species belonging to this group are protogynous; the filaments are erect, and are either adherent or else parallel to the ovary or style. At first the anthers are so far from the stigma that the pollen would not of itself dust the stigma in the same flower, but the subsequent elongation of the filaments is so regulated as to carry the anthers to the same level as the stigma by the time they are coated with pollen. The anthers then adhere to the receptive stigmatic tissue, and autogamy is the result. The following are instances of plants