E. Series, ½, 2/5, 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.
Fig. 45 a.