Imagini ale paginilor

fronds, apparently bearing on parts of the main stem or petiole small rounded sporocarps. They are found abundantly in the Middle Erian of the State of New York, and also occur in Scotland, while one species appears to occur in Nova Scotia, as high as the Lower Carboniferous (Figs. 17, 18).

These organisms have been variously referred to Lycopods, to Algæ, or to Zoophytes, but an extended compari

[graphic][ocr errors][subsumed]

Fig. 18.-Ptilophyton Thomsoni (Scotland). a, Impression of plant in

vernation. 5, Branches conjecturally restored. C, Branches of Lycopodites Milleri, on same slab.

son of American and Scottish specimens has led me to the belief that they were aquatic plants, more likely to have been allied to Rhizocarps than to any other group. Some evidence of this will be given in a note appended to this chapter.



genus, which I have named Psilophyton * (Figs. 19, 21), may be regarded as a connecting link between the Rhizocarps and the Lycopods.

It is so named from its resemblance,

in some spects, to the curious parasitic Lycopods placed in the modern genus Psilotum. Several species have been described, and they are eminently characteristic of the Lower Eri. an, in which they were first discovered in Gaspé. ical species, Psilophyton princeps, which fills many beds of shale and sandstone in Gaspé Bay and the head of the neighbouring Bay des Chaleurs with

its slender stems and Fig. 19. -- Psilophyton princeps, restored creeping, cord-like rhi

(Lower Erian, Gaspé). a, Fruit, natural size. b, Stem, natural size. C, Scalari- zomes, may be thus deform tissue of the axis, highly magni- scribed : fied. In the restoration, one side is represented in vernation and the other in fruit, Stems branching


The typ

*“Journal of the Geological Society," vols. XV., xviii., and xix., “Re. port on Devonian Plants of Canada," 1871.

[ocr errors]


dichotomously, and covered with interrupted ridges. Leaves rudimentary, or short, rigid, and pointed ; in barren stems, numerous and spirally arranged ; in fertile stems and branchlets, sparsely scattered or absent; in decorticated specimens, represented by minute punctate scars. Young branches circinate ; rhizomata cylindrical, covered with hairs or ramenta, and having circular areoles irregularly disposed, giving origin to slender cylindrical rootlets. Internal structure-an axis of scalariform vessels, surrounded by a cylinder of parenchymatous cells, and by an outer cylinder of elongated woody cells. Fruc- FIG. 20, -- Sphe

nophyllum tification consisting of naked oval spore- tiquum (Erian,

New Brunswick). cases, borne usually in pairs on slender,

See pp. 61, 67. curved pedicels, either lateral or terminal.

This species was fully described by me in the papers referred to above, from specimens obtained from the rich exposures at Gaspé Bay, and which enabled me to illustrate its parts more fully, perhaps, than those of any other species of so great antiquity. In the specimens I had obtained I was able to recognise the forms of the rhizomata, stems, branches, and rudimentary leaves, and also the internal structure of the stems and rhizomata, and to illustrate the remarkable resemblance of the forms and structures to those of the modern Psilotum. The fructification was, however, altogether peculiar, consisting of narrowly ovate sporangia, borne usually in pairs, on curved and apparently rigid petioles. Under the microscope these sporangia show indications of cellular structure, and appear to have been membranous in character. In some specimens dehiscence appears to have taken place by a slit in one side, and, clay having entered into the interior, both walls of the spore-case can be seen. In other instances, being flattened, they might be mis



taken for scales. No spores could be observed in any of the specimens, though in some the surface was marked by slight, rounded prominences, possibly the impressions of the spores within. This peculiar and very simple style

[ocr errors][merged small]

FIG. 21. Lepidodendron and Psilophyton (Erian, New Brunswick).

A, Lepidodendron Gaspianum. B, C, Psilophyton elegans.

of spore-case is also characteristic of other species, and gives to Psilophyton a very distinct generic character. These naked spore-cases may be compared to those of such lycopodiaceous plants as Psilotum, in which the scales are rudimentary. They also bear some resemblance, though on a much larger scale, to the spore-cases of some Erian ferns (Archæopteris), to be mentioned in the sequel. On the whole, however, they seem most nearly related to the sporocarps of the Rhizocarpeæ.

Arthrostigma, which is found in the same beds with Psilophyton, was a plant of more robust growth, with better-developed, narrow, and pointed leaves, borne in a verticillate or spiral manner, and bearing at the ends of its branches spikes of naked sporocarps, apparently similar to those of Psilophyton but more rounded in form. The two genera must have been nearly related, and the slender branchlets of Arthrostigma are, unless well preserved, scarcely distinguishable from the stems of Psilophyton. *

If, now, we compare the vegetation of these and similar ancient plants with that of modern Rhizocarps, we shall find that the latter still present, though in a depauperated and diminished form, some of the characteristics of their predecessors. Some, like Pilularia, have simple linear leaves; others, like Marsilea, have leaves in verticils and cuneate in form ; while others, like Azolla and Salvinia, have frondose leaves, more or less pinnate in their arrangement. The first type presents little that is characteristic, but there are in the Erian sandstones and shales great quantities of filamentous and linear objects which it has been impossible to refer to any genus, and which might have belonged to plants of the type of Pilularia. It is quite possible, also, that such plants as Psilophyton glabrum and Cordaites angustifolia, of which the fructification is quite unknown, may have been allied to Rhizocarps. With regard to the verticillate type, we are at once reminded of Sphenophyllum (Fig. 20), which

* Reports of the auther on “Devonian Plants,” “Geological Survey of Canada,” which see for details as to Erian Flora of northeastern America.

« ÎnapoiContinuați »