From the disappearance of many of those anomalous types of the Coal Measures which so puzzle the botanist, and the extensive introduction of types that still exist, we can better conceive of the general features and relations of the flora of the Oolite than of those of the earlier floras. And yet the general result at which we arrive may be found not without its bearing on the older vegetations also. Throughout almost all the families of this Oolitic flora, there seems to have run a curious bond of relationship, which, like those ties which bound together some of the old clans of our country, united them, high and low, into one great sept, and conferred upon them a certain wonderful unity of character and appearance. Let us assume the ferns as our central group. Though less abundant than in the earlier creation of the Carboniferous system, they seem to have occupied, judging from their remains, very considerable space in the Oolitic vegetation; and with the ferns there were associated in great abundance the two prevailing families of the Pterides,—Equiseta and Lycopodia,—plants which, in most of our modern treatises on the ferns proper, take their place as the fern allies. (See [Fig. 148.]) Let us place these along two of the sides of a pentagon,—the Lycopodia on the right side of the ferns, the Equiseta on the left; further, let us occupy the two remaining sides of the figure by the Coniferæ and the Cycadaceæ,—placing the Coniferæ on the side next the Lycopodia, and the Cycadaceæ, as the last added keystone of the erection, between these and the Equiseta. And now, let us consider how very curious the links are which give a wonderful unity to the whole. We still find great difficulty in distinguishing between the foliage of some of even the existing club mosses and the conifers; and the ancient Lepidodendra are very generally recognized as of a type intermediate between the two. Similar intermediate types, exemplified by extinct families, united the conifers and the ferns. The analogy of Kirchneria with the Thinnfeldia, says Dr. Braun, is very remarkable, notwithstanding that the former is a fern, and that the latter is ranked among conifers. The points of resemblance borne by the conifers to the huge Equiseta of the Oolitic period seem to have been equally striking. The pores which traverse longitudinally the channelled grooves by which the stems of our recent Equiseta are so delicately fluted, are said considerably more to resemble the discs of pines and araucarians than ordinary stomata. Mr. Francis does not hesitate to say, in his work on British Ferns, that the relation of this special family to the Coniferæ is so strong, both in external and internal structure, that it is not without some hesitation he places them among the fern allies; and it has been ascertained by Mr. Dawes, in his researches regarding the calamite, that in its internal structure this apparent representative of Equiseta in the earlier ages of the world united "a network of quadrangular tissue similar to that of Coniferæ to other quadrangular cells arranged in perpendicular series," like the cells of plants of a humbler order. The relations of the Cycadacean order to ferns on the one hand, and to the Coniferæ on the other, are equally well marked. As in the ferns, the venation of its fronds is circinate, or scroll-like,—they have in several respects a resembling structure,—in at least one recent species they have a nearly identical form; and fronds of this fern-like type seem to have been comparatively common during the times of the Oolite. On the other hand, the Cycadaceæ manifest close relations to the conifers. Both have their seeds originally naked; both are cone-bearing; both possess discs on the sides of their cellules; and in both, in the transverse section, these cellules are subhexagonal, and radiate from a centre. Such were the very curious relations that united into one great sept the prevailing members of the Oolitic flora; and similar bonds of connection seem to have existed in the floras of the still earlier ages.
IMBRICATED STEM.
(Helmsdale.)
(Helmsdale.)