Art. LXXIV.—On the Root-stock of Marattia fraxinea, Smith.
[Read before the Wellington Philosophical Society, 29th August, 1877.]
The root-stock, or rhizome of Marattia, is described by Hooker, in the “Flora of New Zealand,” as “a large-rounded, hard, fleshy mass, as large as the head,” and, in the “Handbook of the New Zealand Flora,” as “a large tuberous rhizome.” Again, De Vriese and Harting, in their “Illustrated Monograph of Ferns,” published at Leyden, in 1853, describe it as “a succulent irregularly-shaped tuberous mass upon which the stems are articulated.”
As no additional information is given in the more recent accessible work on Ferns, “Species Filicum of Hooker and Baker,” I have been induced to place before the Society the result of observations made on the New Zealand species of this genus Marattia fraxinea, Sm., as to its method of reproduction by the root, which may add to our knowledge on this subject. The rhizome, or root-stock of the New Zealand species, is composed of an irregular agglomerated mass of thick fleshy scales, each scale being formed by the enlargement of a stipe base, the stipe separating by an articulation above the swelling, after the frond has performed its functions. The articulated surface of the scale shows a scar mark much resembling the imprint of a horse-hoof.
Such a root-stock approaches the scaly bulb more in structure than a fern rhizome, but without a central mass round which the scales might be arranged in order.
The continued addition of new scales outwards and upwards often raises the rhizome above the surface of the ground, but the frond-buds of those scales only which are in contact with the soil throw out independent roots.
This form of root-stock may therefore be named a scaly sub-ariel rhizome, without internodes.
The procedure in propagating in Marattia by scales is very similar to that of the common Potato. When the plant is grown from a detached scale, the buds may sprout from any part of its surface, differing in this respect from the potato in having neither points or eyes, and when a frond springs from the crown of the rhizome, or from a scale above the surface of the ground, it derives its nourishment through the parent scales.
The bud swells to a considerable size before the crozier bursts through the cuticular bark. During this process the latter is split and the edges carried upwards, forming the so-called adnate stipules of authors, and remain as a sharp ridge round the scar where the stipe articulated. The new stipe begins to swell at its base at a very early period, spreading over the adjacent surface, and forming a new scale.
The growth of the Marattia rhizome is remarkably slow, being under favorable circumstances only one inch diameter in one year, and as the height is less than the diameter it may be safely calculated that a Maori will consume in one day the growth of five years, which fact may account for this fern disappearing in New Zealand wherever the Maoris are numerous. The rhizome, by a process of renewal and movement, lives for an indefinite time, shifting its position in the ground by its growth outwards from a centre, the exhausted scales accumulating in a hard mass on the original site. In this way, like certain fungi, rings or detached clumps may be formed at equal distances from the centre, if no obstructiou exists. Before the exhaustion of the rhizome mass, adventitious frond-buds sprout from various parts of its surface above or beneath the soil.
Description of Plate XVIII.
Fig. 1.—Front view of a scale half the natural size. It is composed of cellular tissue filled with starch grains, fibro-vascular bundles, and covered by an adhering bark. The cut section shows numerous small orange-coloured spots, which exude on the surface, when newly cut, a viscid gum-resinous matter.
Fig. 2.—A scale after three months in the ground, showing the method of bud growth with roots proceeding from the bottom of the bud. Half the natural size.
Figs. 3 and 4 are two illustrations of the frond growth above ground, showing the croziers in two stages of development, and the formation of the adnate stipules. Half the natural size.
Fig. 5.—Root process, showing rootlets proceeding chiefly from the lower side of root; the whole very flexible. Half the natural size.
Figs. 6 and 7 A.—Sections of root enlarged. The chief component mass is cellular tissue and starch grains, with lacunæ. There is also a starshaped
shaped nuclei of fibro-vascular and scalariform bundles. The bundles distinctly wedge-shaped, the root thus showing a stronger affinity in structure to the Equisetaceœ than to Ferns, and presenting an additional reason to the difference in Sporangia, why Marattiaceœ should be separated from Ferns.
Fig. 7.—Starch grains of Marattia fraxinea, Sm.
Note.—I am also of opinion, although requiring longer observation to prove satisfactorily, that the rhizomes of the New Zealand Botrychium and Ophioglossum are built up, or added to, by a similar method to that of Marattia.