Sept. 2o, 1883] 



NATURE 



505 



most of the plants included in the genera Psaronius, Caulopteris, 

 and Protopteris, are also tree-ferns. 



There yet remains another remarkable group of ferns, the 

 sporangia of which are known to us through the researches of 

 M. Renault. In these the fertile pinnules are more or less com- 

 pletely transmuted into small clusters of oblong sporangia. In 

 one case M. Renault believes that he has identified these organs 

 with a stem or petiole of a type not uncommon at Oldbam and 

 Halifax, belonging to Corda's genus Zygopteris. Renault has 

 combined this with some others to constitute his group of 

 Botryopttridles, an altogether extinct and generalised type. This 

 review shows that whilst forms identifiable with the Hymeno- 

 phyllacea and Marattiacca existed in the Carboniferous epoch, 

 and we find here and there traces of affinities with some other 

 more recent types, most of the Carboniferous ferns are generalised 

 primaeval forms which only become differentiated into later ones 

 in the slow progress of time. 



Equistiacea and Asterophyttitta, Brong. Calamaria-, End- 

 licher. Equise/inee, Schimper. 



Confusion culminates in the history of this variously-named 

 group. Hence the subject is a most difficult one to treat in a 

 concise way. The confusion began when Brongniart separated 

 the plants contained in the group into two divisions — one of which 

 {Equise'tace's) he identified with the living Equisetums, and the 

 other (Asterophy/htees) he regarded as being Gymnospermous 

 Dicotyledons. To Schimper belongs the merit, as I believe it 

 to be, of steadily resisting this division ; nevertheless, palceo- 

 botanists are still separated into two schools on the subject ; 

 Dawson, Renault, Grand-Eury, and Saporta adhere to (he 

 Brongniartian idea, whilst the British and German paleontolo- 

 gists have always adopted the opposite view, rejecting the idea 

 that any of these plants were other than Cryptogams. 



A fundamental feature of the entire group is in the fact that 

 their foliar appendages, however morphologically and physio- 

 logically modified, are arranged in nodal verticils. This appears 

 to be the only characteristic which the plants possess in 

 common. 



Catamites and Calamodcndron. In his "Prodrome" (1828), 

 and in his later "Vegetaux Fossiles,' Brongniart adopted the 

 former of these generic names as previously employed by Suckow, 

 Schlotheim, Sternberg, and Artis. It was only in his "Tableau 

 des Genres de Vegetaux Fossiles" ("Dictionnaire universe! 

 d'Histoire Naturelle," 18 9) that he divided the genus, intro- 

 ducing the second name to repre-ent what he believed to be the 

 Gymnospermous division of the group. A long series of inves- 

 tigations, extending over many years, has convinced me that no 

 such Gymnospermous type exists. 1 The same conclu-ion has 

 more recently been arrived at by Voin c. M. D. Stur, : after 

 studying many continental examples in which structure is 

 preserved. What I regard as an error appears to have had 

 an intelligible origin — the fertile source of similar errors in other 

 groups. 



Nearly all the Calamitean fossils found in shales and sand- 

 stones consist of an inorganic, superficially fluted substance, 

 coated over with a thin film of structureless coal (see " Histoire 

 des Vegetaux Fossiles," Vol. i., PI. 22), the latter being exactly 

 moulded upon and following the outlines of tlie inorganic fluted 

 cast thai underlies it. Brongniart and those who adopt his 

 views believe that the external surface of this coal-film exactly 

 represents the corresponding external surface of the original 

 plant. Hence the conclusion was arrived at that the plant had a 

 very large central fistular cavity surrounded by a very thin layer 

 of cellular and vascular tissues as in some living Equisetums. On 

 the other hand, Brongniart also obtained some specimens of 

 what he primarily believed to be Calamites, in which the central 

 pith was surrounded by a thick layer of woody tissue arranged 

 in radiating laminated wedges, separated by medullary rays. 

 The exogenous structure of this woody zone was too obvious to 

 escape his practised eye. But, not supposing it possible that 

 any Cryptogam could pos-ess a cambium-layer and an exogenous 

 mode of development, Brongniart came to the conclusion that 

 the thin-walled specimens found in the shales and sandstones 

 were true Equisetacca-, those with the thick woody cylinders 

 being exogens of another type. His conclusion that they were 

 Gymnosperms was a purely hypothetical one, justified by no one 

 feature of their organisation. 



My researches, based upon a vast number of specimens of all 

 sizes, from minute twigs little more than the thirtieth of an inch in 

 diameter, to thick stems at least thirteen inches across, led me to 



1 " Memoirs" i. ix and xii. 



2 " Zur Morphologie der Calamarien.' 



the conclusion that we have but one type of Calamite ; and that 

 the differences which misled Brongniart are merely due to varia- 

 tions in the mode of their preservation. 1 It became clear to me 

 that the outer surface of the coaly film in the specimens pre- 

 served in the shales and sandstones did not represent the outer 

 surface of the living plant, but was only a fractional remnant of 

 the carbon of that plant which had undergone a complete meta- 

 morphosis ; the greater part of what originally ex i ted bad dis- 

 appeared, probably in a gaseous state, and the little that remained, 

 displaying no organic structure, had been moulded upon the under- 

 lying inorganic cast of the medullary cavity. This cast is 

 always fluted longitudinally and constructed transversely at inter- 

 vals of varying lengths. Both these features were due to 

 impresions made by the organism upon the inorganic sand or 

 mud filling the medullary cavity whilst it was in a plastic state, 

 and which subsequently became more or less hardened ; the 

 longitudinal grooves being caused by the pressure of the inner 

 angles of the numerous longitudinally vascular wedges, and the 

 transverse ones partly by the remains of a cellular nodal dia- 

 phragm, which crossed the fistular medullary cavity, and partly 

 by a centripetal encroachment of the vascular zone at each of 

 the same points. 5 



My cabinets contain an enormous number of sections of these 

 plants in which the minute-t details of their organisation are 

 exquisitely preserved. These specimen*, as already obferved, 

 show their structure in every stage of their growth, from the 

 smallest twigs to stems more than a foot in diameter. Yet the-e 

 various examples are all, without a solitary exception, constructed 

 upon one common plan. That plan is an extremely complicated 

 one ; far too complex to make it in the slightest decree probable 

 that it could coexist in two such very different orders of plants 

 as the EijuisetacctT and the Gymuospervne : yet, though very 

 complex, it is, even in many of its minuter details, unmistakably 

 the plan upon which the living Equisetums are constructed. The 

 resemblances are too clear as w< 11 as too remarkable, in my mind, 

 to leave room for any doubt on this point. The great differences 

 are only such as necessarily resulted from the gradual attainment 

 of the arborescent form so unlike the lowly herbaceous one of 

 their living representatives. On the other hard, no living Gym- 

 nosperm possesses an organisatr n that in any solitary feature 

 resembles that of the so called Calamodendra. The two have 

 absolutely nothing in common ; hence the conclusion that these 

 Calamodendra were Gymnospermous plants is as arbitrary an 

 assumption as could possibly be forced upon science ; an assump- 

 tion that no arguments derived from the meiely external aspects 

 of structureless specimens could ever induce me to accept. 



These Calamites exhibit a remarkable morphological charac- 

 teristic which presents itself to us here for the first time, but 

 which we shall find recurs in other Palaeozoic forms. Some of 

 our French botanical friends group the various structures con- 

 tained in plants into several " Appartik,"* distinguished by the 

 functions which those structures have to perform. Amongst 

 others we find the " Appareil de sou/ient," embracing those hard 

 woody tissues which may be regarded as the supporting skeleton 

 of the plant, and the "Appareil conducteur," which M. van 

 Tieghem describes as composed of two tissues : " Le tissu crible 

 qui transports essentiellement les matieres insolubles, et le tissu 

 vasculaire qui conduit l'eau et les substances dissoutes." Without 

 discussing the scientific limits of this definition, it suffices for my 

 present purpose. In nearly all flowering plants these two 

 " Appareit 's" are more or less blended. The supporting wood 

 cells are intermingled in varying degrees with the sap-conducting 

 vessels. It is so even in the lower Gymnosperms, and in the 

 higher ones these wood cells almost entirely replace the vessels. 

 It is altogether otherwise with the fossil Cryptogams. The 

 vascular cylinder in the interior of the Calamites, for example, 

 consists wholly of barred vessels, a slight modification of the 

 scalariform type so common in all Cryptogams. No trace of 

 the " Appareil de soutiens " is to be found amongst them. The 

 vessels are, in the most definite sense, the " Appareil 's conduc- 

 teurs " of these plants ; no such absolutely undifferentiated unity 

 of tissue is to be found in any living plants other than 

 Cryptogams. 



But these Calamites, when living, towered high into the air. 

 My friend and colleague, Professor Boyd Dawkins, recently 

 assisted me in measuring one found in the roof of the Moorside 

 colliery near Ashton-under-Lyne by Mr. George Wild, the very 

 intelligent manager of that and some neighbouring collieries. 



1 " Memoirs"!, and ix. 



2 See *' Memoir" i. PI. xxiv. Fig. 10, and PL xxvi. Fig/24. 



3 Van Tieghem, "Traite - de Botanique." p. 679. 



