An analysis of the British ferns and their allies / By G.W. Francis.

  • Francis, George William, 1800-1865.
Date:
1842
Catalogue details

Licence: Public Domain Mark

Credit: An analysis of the British ferns and their allies / By G.W. Francis. Source: Wellcome Collection.

    29/122 (page 17)
    order, and which it will be recollected there, as here, are arranged in longitudinal lines. A transverse section of the stem shows that between the outer and inner cuticle is a circle (and in Equisetum fluviatile two circles, alternating with each other), of tubes, distinct from each other, but terminating at every joint of the stem ; fresh tubes of a similar character being found at every other joint. Around these tubes, and especially towards the outside of the whole stem, and seated immediately under the cuticle, are the sap vessels of the plant, which appear flat, spiral, perforated ducts, as in the other orders. The inner surface of the stem is frequently more silicious than the outer, forming a very beautiful object even to the naked eye. So abundant is this deposit in Equisetum hyemale, that, after the vegetable matter has been removed by maceration, the silex has been sufficiently abundant to retain the form of the plant. M. John, of Berlin, states that the stems contain full 13 per cent, of silica. The following interesting particulars of the silicious cuticle of Equisetum is given in Dr. Greville’s excellent “ Flora Edinensis,” p. 214. “ On subjecting a portion of the cuticle to the analysis of polarized light under a high magnifying power, Dr. Brewster detected a beautiful arrangement of the siliceous particles, which are distributed in two lines parallel to the axis of the stem, and extending over the whole surface. The greater number of the particles form simple straight lines, but the rest are grouped into oval forms, connected together like the jewels of a necklace, by a chain of particles forming a sort of curvi-linear quadrangle ; these rows of oval combinations being arranged in pairs. Many of those particles which form the straight lines do not exceed the 500th part of an inch in diameter. Dr. Brewster also observed the remarkable fact, that each particle has a regular axis of double refraction. In the straw and chaff of wheat, barley, oats, and rye, he noticed analogous phenomena, but the particles were arranged in a different manner, and “ displayed figures of singular beauty.” From these data, the learned Doctor concludes, “that the crystalline portions of silex, and other earths which are found in vegetable films, are not foreign substances of accidental occurrence, but are integral parts of the plant itself, and probably perform some important function in the processes of vege- table life.”—Brewster, MS. REPRODUCTION.—The reproductive organs are borne in a terminal spike or catkin, composed of hexagonal or octagonal shields ; from each side of which depend hollow, scale-like follicles, opening inwardly, and emitting green, ovate spores, to each of which is attached four club-shaped filaments. When the spores are immature, the filaments are twisted tightly round them, but when ripe they become exceedingly elastic and hygrometrical, so much so, that the irritability occasioned by a change of temperature or moisture, causes the spores first to burst the thecse which bear them, and afterwards to scatter themselves to a considerable distance. A valuable paper upon the formation of the spores, by Mr. Henderson, was read before the Linnsean Society, in June 1840 ; and will be found in their “ Transactions,” vol. xviii. p. 567. The experiments of this gentleman exactly