ture has not hitherto been determined. The different forms have been placed together as allied genera, and have been referred, by those who have specially studied them, to the phanerogamous Order Haloragaceae near to the Water Milfoil (Myriophyllum), with some species of which they agree very remarkably in the arrangement and aspect of their foliage and fruit.1

PLATE II.-FRUITS OF EQUISETUM AND CALAMITES.

Fig. 1. Equisetum arvense, L. 2. Portion of the sporangium wall. 3. Spore, with the elaters free. 4. Spore with the elaters clasping. 5. Longitudinal section of the part of one side of cone with three fruit-bearing scales supporting sporangia. 6. Transverse section of cone. 7. Calamites (Volkmannia) Binneyi, Carr., magnified three times. 8. Portion of the sporangium wall. 9. Two spores, one showing the bases of two elaters free, the remainder being removed in slicing the fossil, and the other showing the elaters clasping. 10. Longitudinal section of part of one side of cone with three fruit-bearing and four simple leaves. 11. Transverse section of cone, showing six fruit-bearing leaves and twelve protecting scales.

The determination of the internal structure of one of these fruits which I made, first from specimens collected by Mr. Binney, and have since confirmed from specimens which have been some years 1 Monographie des Sphenophyllum d'Europe. Par E. Coemans and J. J. Kickz. Bulletin Acad. Roy. de Belgique, 2nd Ser. vol. xviii. (1864), No. 8.

in the cabinet of Dr. Millar, has enabled me to refer these fossils with certainty to the cryptogamous Order Equisetacea as near allies of our living Horsetails.

This fruit, to which I have given the name Volkmannia Binneyi,' is a small slender cone, composed of whorls of imbricated scales (twelve in each), arranged like the successive whorls of leaves on the branch, so that the scales of one whorl are in a line with the spaces between the scales in the whorls above and below. The scales completely conceal the fruit-bearing leaves. These are stalked and peltate, arranged in whorls alternating with the scales, but having only six-half the number of the scales in a whorl. The sporangia, four in number, are borne on the under-surface of the peltate leaves; their walls are formed of elongated cells, which have in their interior a secondary deposit of cellulose proceeding in short truncate processes from the sides of the cell-walls which are in contact, and having the appearance of an incomplete spiral. The sporangia are filled with simple spherical spores, which in the closely-packed sporangium appear to be furnished with double cell-walls. In the half-empty sporangia the outer wall cannot be detected, but there appear instead a number of thread-like processes proceeding from the spore like the elaters in the living Horsetails.2

A comparison of this fossil cone with the fruit of Equisetum exhibits a remarkable agreement in every point of importance. In the form of the fruit-bearing leaves, the arrangement and structure of the sporangia, the form, size, and structure of the spores. even to the possession of hygrometric elaters, both fruits agree. The only difference is that in the modern plant all the leaves of the cone are fruit-bearing, while in the fossil every other whorl retains a form closely approaching that of the normal leaf of the plant. As these envelope and protect the fruit-bearing leaves, they may be held to give to the fossil a somewhat higher systematic position than is possessed by the living genus. This superiority is further exhibited when we contrast the complex structure of the stem, and the free leaves of Calamites with the fistular and sheath-bearing stems of Equisetum.

III. The stems, branches, and fruit of the genus Lepidodendron, are so abundant in the shales that cover the coal, that the external aspect of this tree has been for a long time well known. Specimens exhibiting structure are more rare, but these also have been met with, so that we know the internal organization as well as the external aspect of the fossil.3

The stem is composed of a central pith surrounded by a slender cylinder of scalariform woody tissue, and by a large cortical layer

1 Prof. Schimper has more recently described and figured the same fruits under the name of Calamostachys Binneyana in his Traité de Paléontologie Végétale, vol. i. (1869), p. 330.

2 Mr. Binney has beautifully illustrated the structure of the stem and fruit of Calamites in a series of drawings from specimens in his rich collection, published by the Palæontographical Society in the end of last year.

3 On some Fossil Plants, showing structure. By E. W. Binney. Quart. Journ. Geol. Soc. vol. xviii. (1862), p. 106, Pl. 4-6. Phil. Trans., 1865.

which is divided into two portions, an inner consisting of large spherical and thin-walled cells, and an outer made up of regularly arranged elongated cells with a small diameter. The vascular cylinder is penetrated by radiating meshes through which the vascular bundles passed that supplied the leaves. The outer surface of the stem is covered with the spirally arranged and beautifully marked stigmata of the fallen leaves. The stem branches repeatedly in a dichotomous manner. The younger branches are densely covered with small lanceolate leaves, having a single median vein.

PLATE III.-FRUITS OF SELAGINELLA AND TRIPLOSPORITES.

Fig. 1. Selaginella spinulosa, A. Braun. 2. Scale and sporangium from the upper portion of the cone. 3. Antheridian microspores from ditto. 4. Macrospore. 5. Scale and sporangium from the lower part of the cone containing macrospores. 6. Triplosporites Brownii, Brongn. 7. Three scales and sporangia of ditto. 8. Microspores from the sporangia of the upper part of the cone. 9. Macrospore from the sporangia of the lower part (drawn from Brongniart's description and measurements). 10. Scales and sporangia of a cone of Flemingites.

The fruit is a cone composed of imbricated scales arranged spirally on the axis like the true leaves, and bearing the sporangia on their

horizontal pedicels. Three different forms of fruit belong to this genus, or it should perhaps rather be called group of plants.

The first of these is the cone named by Robert Brown Triplosporites,1 and described by him from an exquisitely preserved specimen of an upper portion, in which the parts are exhibited as clearly in the petrified condition as if they belonged to a fresh and living plant. The large sporangia have a double wall, the outer composed of a compact layer of oblong cells placed endwise, or with the long diameter perpendicular to the surface; the inner is a delicate cellular membrane. The sporangium is filled with a great number of very small spores, each composed of three roundish bodies or sporules. Recently Professor Brongniart has described a complete specimen of this fruit, in which the minute triple spores are confined to the sporangia of the upper and middle part of the cone, but the lower portion, which was wanting in Mr. Brown's specimen, bears sporangia filled with simple spherical spores ten or twelve times larger than the others.

The structure of another form of cone (Lepidostrobus) has been expounded by Dr. Hooker. The arrangement of the different parts comprising it is precisely similar to what occurs in Triplosporites ; but the sporangia are filled with the minute triple spores throughout the whole cone.

The third form of cone, which I have described under the name Flemingites, differs from the other two in having a large number of small sporangia supported on the surface of each scale; and it agrees with Lepidostrobus in the sporangia containing only small spores.

In comparing these fossils with the living club-mosses, one is struck with the singular agreement in the organization of plants so far removed in time, and so different in size, as the recent humble club-mosses and the palæozoic tree Lepidodendrons.

The fruit of Triplosporites, like that of Selaginella, contains large and small spores, the microspores being found in both genera on the middle and upper scales of the cone, and the macrospores on those of the lower portion.

On the other hand, the fruits of Lepidostrobus and Flemingites agree with those of Lycopodium in having only microspores.

The size of the two kinds of spores also singularly agrees in the two groups. This is of some importance, for among the recent vascular cryptogams there is a remarkable uniformity in the size of the spores in the members of the different groups, even when there is a great variety in the size of the plants. Thus the spore of our humble Wall-rue is as large as that of the giant Alsophila of tropical

1 Some account of Triplosporite. By R. Brown. Trans. Linn. Soc. vol. xx. (1851), p. 469, Pl. 33 and 34.

2 Notice sur un fruit de Lycopodiacées fossiles. Par M. Brongniart. Comptes Rendus, vol. lxvii., Aug. 17, 1868.-Translated in Seemann's Journal of Botany, vol. vii. (1869) p. 1.

On the Structure and Affinities of some Lepidostrobi. By J. D. Hooker. Memoirs of Geol. Surv., Vol. ii., Pt. 2 (1848), p. 440, Pl. 3-10.

On an Undescribed Cone from the Carboniferous Beds. GEOL. MAG., Vol. II. (1865), p. 433. Pl. 12.

regions. So also the spores of Equisetum and Calamites agree in size, as may be seen in Plate II., Figs. 3, 4, and 9, where the spores of the two genera are magnified to the same extent. And a similar comparison of the macrospore and microspore of Triplosporites with those of Selaginella, and of the microspore of Lepidostrobus with that of Lycopodium, exhibits a similar agreement. This is made apparent by the drawings of the two kinds of spores of Selaginella on Plate III., Figs. 3 and 4, with those of Triplosporites, Figs. 8 and 9, which are drawn to the same scale.1

.

The fossils represented by the group of stems known under the name of Lepidodendron, and by the three fruits described, agree in all essential characters with the living Club-mosses, the only difference of importance being that the stem of the fossil has a higher organization suited to its arborescent habit. The vascular tissue continued to increase with the growth of the plant somewhat like an exogenous stem. In all the living vascular cryptogams, the vascular tissue is produced at once in its full extent except in Isoetes, which has a cambium layer surrounding the cylinder of wood in which as the plant grows new vascular tissue is developed. The zone of thinwalled spherical cells which surrounds the woody cylinder in Lepidodendron, and which is so rarely preserved, has been a true cambium layer like that in Isoetes. But for the existence of this small water-plant, the large trees of the coal-forests would present in the growth of their stems an inexplicable anomaly.

2

Sigillaria, a very abundant Carboniferous fossil, is a member of the same family as Lepidodendron. Its stem is rarely preserved so as to exhibit structure, the only specimen hitherto described being S. elegans, Brongn.; but its roots are frequently found in a very perfect condition. The name Stigmaria was given to the roots at a time when they were supposed to be independent plants. Their relation to Sigillaria was suggested by Prof. Brongniart from the correspondence in their structure, by Sir W. Logan from the position the two fossils occupied in the beds in which they occur, and the matter was finally set at rest when Mr. Binney observed the roots and stems in actual continuity.

As the structure and arrangement of corresponding parts in the same plant are uniform, as of the root, stem, branches, and axis of the cone, we may supply the want of information regarding the stem by that which can be obtained from the root.

The root is composed of a central medulla surrounded by a cylinder of scalariform tissue, and this again is invested by a large cellular layer. The vascular cylinder is broken up by meshes through which passed the vascular bundles to the rootlets. There are no traces whatever of medullary rays in the wood. The supposed medullary rays which have been described in Sigillaria are the accidental results of desiccation in particular specimens. The internal structure

1 I have given the precise measurement of these spores in a Notice of some Plant Remains from Brazil. GEOL. MAG., Vol. VI. (1869), pp. 153, 154.

2 Observations sur la Structure intérieure du Sigillaria elegans. Par A. Brongniart. Archives du Mus., Vol. i. (1831) p. 405.