Part 11

(1.) Lepidodendron (Possil Ironstone series). Stem about ¾ of an inch in diameter. Secondary spirals 8 D, 13 S, 21 D. Divergence = 13/34 (or possibly 21/55).

(2.) Lepidodendron (Knightswood, near Glasgow, Mr. J. Young). Stem about 1½ inch in diameter. Secondary spirals 13 D, 21 S, 34 D. Divergence = 21/55.

(3.) Lepidodendron (Possil Sandstone series). Trunk about 2 feet long, with an average diameter of 20 inches. Steepest secondary spirals 55 S, 89 D. Divergence = 55/144.

(b.) Conjugate spirals.

(4.) Lepidostrobus ornatus (Bathgate coal-field). About ¾ of an inch in diameter. Secondary spirals 10 D, 16 S, 26 D, 42 S. Divergence = 13/(34×2) (Bijugate arrangement).

(5.) Lepidostrobus (Plean, Stirlingshire, Mr. Mackenzie). About ½ an inch in diameter. Secondary spirals 9 S, 15 D, 24 S, 39 D. Divergence = 8/(21×3) (Trijugate arrangement).

(6.) Knorria taxina (from collection of Dr. Rankin, Carluke). Somewhat compressed, 2-2½ inches in diameter. Secondary spirals 15 D, 24 S. Divergence = 15/(13×3) (Trijugate arrangement).

(7.) Lepidodendron (from Dr. Rankin's collection). About 1¼ inch in diameter. Secondary spirals 10 D, 15 S, 25 D, 40 S. Divergence = 5/(13×5) (Quinquejugate arrangement).

(8.) Lepidodendron (Dowanhill, Glasgow, Possil Sandstone series). Trunk about 1 foot long, and 1 foot in diameter. The upper portion exhibits secondary spirals 35 D, 56 S, 91 D; thus indicating a 7-jugate arrangement, with divergence = 8/(21×7). The arrangement on the middle and lower portion is indistinct and confused; so much so as to render any determination of the arrangement doubtful.

B. Series, ⅓, ¼, 2/7, 3/11, etc.

(9.) Lepidodendron (Messrs Merry and Cunningham's Clayband Iron-Pit, Carluke). Stem 2 inches in diameter. Secondary spirals 18 S, 29 D, 47 S. Divergence = 21/76.

C. Series, ¼, ⅕, 2/9, 3/14, etc.

(10.) Lepidodendron (R. B. Garden, Edinburgh, Museum). Stem somewhat flattened, 1-1½ inch in diameter. Secondary spirals 9 D, 14 S, 23 D, 37 S. Divergence = 13/60.

(11.) Lepidodendron (Redhaugh, near Edinburgh, Mr. Peach). Stem somewhat flattened, ¾ to ½ inch in diameter. Secondary spirals 9 S, 14 D, 23 S, 37 D. Divergence = 13/60.

D. Series, ⅕, ⅙, 2/11, 3/17, 5/28, etc.

(12.) Knorria taxina (Stockbriggs, Lesmahagow,--Hunterian Museum). About 1 inch in diameter. The specimen consists of a main stem and one of the branches into which it has forked. On the main stem the secondary spirals are 6 D, 11 S, 17 D. Divergence = 5/28 (series, ⅕, ⅙, 2/11, 3/17, 5/28, etc.)--On the branch the secondary spirals are 8 S, 13 D. Divergence = 8/21 (ordinary series, ½, ⅓, ⅖, ⅜, etc.)

E. Series, ½, ⅖, 3/7, 5/12, 8/19, 13/31, 21/50, etc.

(13.) Lepidodendron (from Dr. Rankin's collection). About ⅞ inch in diameter. Secondary spirals 12 D, 19 S, 31 D. Divergence = 21/50.

F. Series, ⅓, 3/10, 4/13, 7/23, 11/36, 18/59, etc.

(14.) Lepidodendron elegans (Possil Ironstone). About 1¼ inch in diameter. Secondary spirals 10 S, 13 D, 23 S, 36 D. Divergence = 18/59.

(15.) Lepidodendron (Possil Ironstone). About 2¼ inches in diameter. Secondary spirals 23 S, 36 D, 59 S, 95 D. Divergence = 47/154.

From the above it is evident that the phyllotaxis of Lepidodendron is extremely variable, as much so perhaps as that of those most variable plants, in this respect, the Cacti. It is also clear that what has been enunciated by Professor Haughton (Manual of Geology, Lond. 1866, pp. 243, 245) as the law according to which the leaves of palæozoic plants were arranged--viz. that of alternate whorls--does not apply to these ancient Lycopods. Lepidodendron aculeatum is noted by Naumann as exhibiting an 8/21 arrangement. (Poggendorff, Annalen, 1842, p. 5.) Professor Alexander Braun (Nov. Acta Ac. C. L. C. xv. 1, pp. 558-9), speaking of the excessive deviation from ordinary arrangements in Equisetaceæ (including Calamites), compares them in this respect with Lycopodiaceæ (including Lepidodendron), saying that in these two families "the utmost limits of the domain of all leaf-arrangement appears to be attained."

Lepidophyllum is certainly leaves of Lepidodendron, the different Lepidophylla belonging to different species of the genus. The slender terminal branches are noticed under the name of Lycopodites. In coal from Fordel Mr. Daw has detected innumerable bodies (Plate III. Figs. 1, 2, 3) which have been shown to be sporangia. (Balfour, Trans. Roy. Soc. Ed. xxi. 187.) On their under surface Mr. Carruthers has observed a triradiate ridge (Plate III. Fig. 4). (Geological Magazine, 1865, vol. ii. p. 140.) These sporangia have been found connected with the cone-like fructification called Flemingites, and resembling Lycopodium (woodcut 44, Fig. 4). Many forms of fossil plants, such as Halonia, Lepidophloios, Knorria, and Ulodendron, belong to the Lepidodendron group. Knorria is said to be the internal cast of a Lepidodendron.

Ulodendron minus and U. Taylori (Plate III. Fig. 11), found in ferruginous shale in the Water of Leith, near Colinton, exhibit beautiful sculptured scars, ranged rectilinearly along the stem. The surface is covered with small, sharply relieved obovate scales, most of them furnished with an apparent midrib, and with their edges slightly turned up. The circular or oval scars of this genus are probably impressions made by a rectilinear range of aerial roots placed on either side. When decorticated, the stem is mottled over with minute dottings arranged in a quincuncial manner, and its oval scars are devoid of the ordinary sculpturings. Bothrodendron is a decorticated condition of Ulodendron.

Calamites (κάλαμος, a reed) is a reed-like fossil, having a sub-cylindrical jointed stem (Fig. 45, a and b; Fig. 46; Plate IV. Fig. 4). The stem is often crushed and flattened, and was originally hollow. Calamites is thus defined by Grand d'Eury (Ann. Nat. Hist. ser. 4, vol. iv. p. 124):--Stem articulated, fistular, and septate; outer part comparatively thin, formed of three concentric zones--1, an exterior cortical layer now converted into coal; 2, a thin subjacent zone of vascular tissue, now invariably destroyed; 3, a sort of inner lining epidermis, which is carbonified. Cortical envelope marked interiorly with regular flutings, interrupted and alternate at the articulations. Inner epidermis smooth, or scarcely striated. Vascular cylinder thin; outer surface of bark more fully fluted and articulated than the inner surface.

Carruthers gives the following description of the structure of a species of Calamite which he examined:--The stem was composed of a central medulla, which disappeared with the growth of the plant, surrounded by a woody cylinder, composed entirely of scalariform vessels, and a thin cortical layer. The medulla penetrated the woody cylinder by a series of regular wedges, which were continued, as delicate laminæ of one or two cells in thickness, to the cortical layer. The cells of those laminæ were not muriform; their longest diameter was in the direction of the axis. The wedges were continuous, and parallel between each node. As the axial appendages were produced in whorls, the only interference with the regularity of the tissues was by the passing out through the stem at the nodes of the vascular bundles which supplied these appendages. As the leaves of each whorl were (with one or two exceptions) opposite to the interspaces of the whorls above and below, there was also at each node a re-arrangement of the wedges of vascular and cellular tissues.

Schimper considers Calamites as having an analogy with Equisetum in its fructification. He looks on them as fossil Equisetaceæ. Annularia and Sphenophyllum are considered as establishing a passage from the Equisetaceæ to the Lycopodiaceæ. Some gigantic fossil Equiseta had a diameter of nearly 5 inches, and a height of 30 or more feet. The branches, which adorned the higher part of them in the form of a crown, are simple, and have at their extremity a spike of the size of a pigeon's egg, and organised exactly like the spikes of living Equiseta. The subterranean rhizomes are well developed, and gave origin, like many Equiseta, to tubercles which had the form and size of a hen's egg.

The characters of Equisetum of the present day and Calamites, are exhibited in woodcut 47. They show a marked resemblance in the fructification. (See also page 31.)