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The United States Coal Flora compared to that of Europe.

§ 41. For the Thalamophytes or marine plants, no point of comparison is found in the European coal flora. The species described in this volume are as yet the only representatives of marine plants found in the coal measures of any country.

§ 42. With few exceptions, the
Calamariae are the same on both continents. All our Calamites except two, insufficiently defined from poor specimens, are European. The, number of species of Calamites is, however, uncertain, as the authors generally differ on the value of the specific characters of these plants. Calamodendron which I have placed in this order belongs to the upper coal measures of Europe, the Permo-Carboniferous and Permian the characters of the plants are recognized mostly from anatomical analysis which we are unable to do here. Of Asterophyllites, three species pertain as yet exclusively to the American flora, and three species also of Sphenophyllum. Annularia species are identical, excepting Annularia inflata, which may be a mere form of Annularia longifolia. I believe, therefore, that when the species of the Calamariae are defined by more complete specimens, scarcely any difference will be remarked between the European and the American representatives of this order.

The genus
Trochophyllum, hypothetically added to this division is formed of two exclusively American plants.

§ 43. In the Ferns, the differences are very great, one third only of the two hundred ninety-four species described from the U. S. Coal Measures being considered identical with those of Europe. This difference seems at first peculiar and might be supposed to result essentially from uncertain determinations, if it were not rendered evident by a number of peculiar distinct types. Merely quoting the more remarkable ones, we have:
Neuropteris laciniata, Neuropteris Rogersi, Neuropteris Clarksoni, Neuropteris Desorii, Neuropteris rarinervis, Neuropteris Agassizi, Neuropteris anomala, Neuropteris verbenaefolia. Neuropteris fimbriata was considered for years a type peculiar to America, but a relative species has been found more recently in the anthracite of the Alpine mountains of Savoy. In Odontopteris, we have: Odontopteris Newberrii, Odontopteris cornuta, Odontopteris heterophylla, Odontopteris Worthenii, Odontopteris subcuneata, Odontopteris gracillima; and then Lesleya grandis, Dictyopteris rubella, all the Megalopteris,*
* Saporta (in letter) says that fragments of large leaves probably referable to this genus have been discovered in France.
Taeniopteris Neriopteris, Orthogoniopteris, Danaeites, Idiophyllum especially, whose characters are without analogy to any coal plant of Europe. In the genera Alethopteris, Pseudopecopteris, Pecopteris, Sphenopteris and Archaeopteris, one half of the species are identical, and most of those considered as distinct have characters striking enough to have been recognized as specific by Schimper, Grand'Eury and other European authors.

The more marked difference is in the species of the genus
Rhacophyllum, of which nineteen are described from American specimens, four of which only are European. These plants appear to have been either parasitic upon other Ferns or sometimes merely protophylles, like the foliaceous patches preceeding the unfolding of stems and fronds of some Ferns. A number of these vegetable organisms are found exclusively in nodules or iron concretions wherein the more delicate parts of plants have been preserved. This may account for the great number of species we have of this genus, and also for the separate fruiting fragments of Ferns described under the name of Sorocladus and of rhizomas, none of which have been discovered in Europe.

The preponderance of Fern-trees in the U.S. coal flora, seen by remains of
Stemmatopteris, Caulopteris, and Megaphytum, was probably caused by peculiar differences in the atmospheric circumstances. Of these genera we have twenty-four species, two of which only, Caulopteris Cistii and Megaphytum McLayi, are identified from Europe.

§ 44. The
Lycopodiaceae have, here as in Europe, entered to a great extent into the composition of the coal. The number of species of this class, recognized in the American coal measures is increased by fructifications, some of these of peculiar conformation, which for the genera Lepidophyllum, Lepidocystis, Sporocystis, have scarcely been described by European authors.

The genus
Lepidodendron is represented in Schimper's Veget. Paleont. by fifty-nine species, deducting the synonyms, thirty to forty in number. Of the species, twelve are identified in the U.S. Coal measures; besides twenty-nine described as new.

For this genus and for
Sigillaria also, the characters we have for determination are merely taken from the scars left on the bark, as points of attachment of the leaves. As they are variable in their characters at different ages, it has been asserted, perhaps with reason, that the number of species is by far too widely increased. I have already remarked on the subject, p. 364. I have only to add, that from the number of species published in these two genera from the European coal flora, it would be rational to come to a contrary conclusion. Schimper, after carefully reducing the number of species by elimination of those considered as synonyms, has still, for Lepidodendron, seven to eight per cent. of the species of the whole coal flora, and for Sigillaria ten per cent., while the Lepidodendron make only six and a half [per cent.] and the Sigillaria eight per cent. of the species described in this flora.

I believe, however, that for these two genera, still more than for the Ferns, the number of species may be reduced hereafter by comparison of American with European specimens, although we have, as for the Ferns, some peculiar types which, without analogy to any of those recognized in Europe, evince the continental character of each flora. Of this kind are
Lepidodendron Brittsii, Lepidodendron latifolium, Lepidodendron squamiferum, Lepidodendron corrugatum, Lepidodendron costatum, Lepidodendron turbinatum, Lepidodendron Worthenii, Lepidodendron diplotegioides, and also (though contested) the common Lepidodendron clypeatum.

Our species of
Lycopodites are also mostly distinct, especially Lycopodites strictus and Lycopodites annulariaefolius. One, Lycopodites Ortoni, belongs to the group of Lycopods with dimorphous leaves (Selaginella), represented in Europe by four different species.

Ulodendron the species are identical except one.

has three identical species, one related and two of peculiar types; while of the Lepidophloios, only two of the eight species described here are identified in Europe.

It is especially in the fructifications of the
Lycopodiaceae: Lepidostrobus, Lepidophyllum, Lepidocystis and Sporocystis, that we have here a number of greatly diversified forms most of them unknown in Europe. These vegetable remains have been obtained mostly in the nodules of Mazon Creek, the shale of the Morris coal, those of Cannelton, and in the intra conglomerate shale (the Campbell's ledge) of Pittston. Of eleven species of Lepidostrobus, and five of Lepidophyllum, three only are European. All the species of Lepidostrobus (Macrocystis) and all those of Lepidocystis and Sporocystis are exclusively American.

The number of fructifications of the
Lycopodiacece, is comparatively far above that of the species of Lepidodendron. The very distinct and peculiar characters of these remains forces upon us the conclusion that the trees of this class of plants were more diversified in genera and species than is generally believed.

§ 45. What is said for the
Lycopodiaceae may be repeated for the Sigillariae, except for the fructifications, of which as yet scarcely anything is known. Possibly the species of Lepidostrobus (Macrocystis) may be referable to Sigillariae. If this were ascertained, the group should be definitely placed with the Lycopodiaceae. But as yet we have no positive proof of the relation. Remains of Macrocystis at Cannelton correspond in abundance to those of Sigillaria monostygma only; for this locality has merely rare specimens of a few other Sigillaria and Lepidodendron.

The number and proportion of species of
Sigillaria to the flora is remarked above. Of the fifty species described here half of them are European. As essentially distinct types besides Sigillaria monostigma we have: Sigillaria reticulata, Sigillaria stellata, Sigillaria Schimperi, Sigillaria corrugata, Sigillaria Massiliensis, Sigillaria acuminata, Sigillaria Pittstoniana and Sigillaria Lacoei.

Remains of
Stigmaria are found everywhere in abundance, as said already, from the lowest to the upper coal strata, over the whole extent of the coal measures. The flora of the Michigan coal is as yet known to me only by the communication of a large number of specimens of Stigmaria. Most of the species or varieties are common to the coal flora of both continents.

The genus
Spirangium is represented in the U.S. Carboniferous by four distinct species, two of which have been found in the sub-conglomerate ledge of Pittston. Until now it has no representatives in that of Europe where plants of this kind appear later, mostly in the Trias.  Spirangium carbonarium, Schp., only, is from the New Red or Lower Permian of Saxony. The author remarks on it that the existence of this vegetable type positively dates from the Permian.

Cordaiteae are particularly interesting on account of its now generally acknowledged relation to the Gymnosperms.

Until 1877, when the flora of Grand'Eury was published, the
Cordiateae were known merely from fragments of leaves, and their affinities were not clearly defined. From the remains described in that work and from the numerous specimens discovered in the U.S. Coal measures, the characters of these plants and their distribution have been more distinctly exposed. The species are difficult to separate. Of thirty referable to this order, and described here as stems, leaves, flowers and fruits, eight only are identified with those of Europe. The differences in typical characters between the plants of both continents are still more striking in this order than in the Sigillariae. Cordaites grandifolius, Cordaites Lacoei, Cordaites diversifolius, Cordaites gracilis, Cordaites radiates, Cordaites costatus, Cordaites serpens, are quite as distinct as species as Cordaistrobus and Desmiophyllum are as genera.

As yet ripe or full grown fruits of Cordaites still attached to stems, have only been found in the U. S. Coal measures.

§ 46. The seeds are described as
Cardiocarpus, Rhabdocarpus, Trigonocarpus and Carpolithes. Those referable to Cardiocarpus are generally small, locally distributed, and of difficult determination. They represent mostly new species. Of the twenty-two described here eighteen are of the sub-conglomerate measures, and of these only five are identified with European ones. Of over fourteen species of Rhabdocarpus three are European, and of Trigonocarpus, mostly sub-conglomerate, we have fifteen species, five of which only are European. This genus, like Cardiocarpus, is in the U.S. Coal measures especially represented in the Sub-conglomerate.

§ 47. After marking the relation and differences in the plants of the Carboniferous of both continents, can we positively assert that the flora represents the vegetation of one and the same epoch ? The climatic circumstances, temperature, atmospheric humidity, etc., being identical at that time over the whole Northern hemisphere, is it not fair to suppose that the plants should be exactly the same here as they were in Europe ?

The geographical distribution of the plants does not merely depend upon the atmosphere. The nature of the land, its mineral compounds, the origin of the vegetable types, their deviations and modifications in passing to species or genera, the transfer of seeds, and a quantity of other causative agents modify the characters of the vegetation and its distribution even at short distances. For example, the bed of coal shale at Morris is the equivalent of that of Mazon Creek; the formation is identifiable over the interval of ten or twelve miles which separates the localities where plants have been most searched for and collected. Now from Mazon Creek we have eighty-five species not seen at Morris, while thirty-five found at Morris have not been seen at Mazon Creek. Setting aside the species of general distribution, the two localities have only fifteen species in common.

The most common vegetable types of the Coal epoch are all identical on both continents. As we have seen above, very few of the American genera are not represented in Europe, and vice versa. Of the species described from the U.S. Carboniferous, as indicated by the table, one hundred and ninety-two, or one-third, are European.

This is sufficient to prove a most intimate correlation of the floras of both continents at the Carboniferous age.