73 



MARIOPTERIS. 



The fronds of Mariopteris are distinguished from those of 

 Pecopteris by the fact that the leaflets are often lobed or toothed, 

 and generally contracted at the base, and especially by the nerva- 

 tion. The axis of the frond also forks repeatedly. 



Frontispiece — Manopteris muricata (Schlotheim). A very 

 common fossil, and one which, like the fronds of many other 

 Carboniferous plants, is very variable. In this variety most of the 

 leaflets are simple, but a few are lobed. The photograph shows the 

 shape of the leaflets and the characteristic nervation. From the (?) 

 Yorkshire coalfield. Natural size. 



Page 49. Mariopteris muricata (Schlotheim). Another 

 variety in which the leaflets are narrower and nearly all lobed. 

 From the (?) Yorkshire coalfield. Slightly reduced. 



THE EQUISETALES. 



The Equisetales, of which our modern Horsetails f£'^w/j^/«^«) are 

 now the sole survivors, were a great and important group in Car- 

 boniferous times. The Palaeozoic Calarnites were unlike the 

 Horsetails in habit, for the Calamites were large forest trees often of 

 considerable height. In other features however, such as the segment- 

 ation of the stem into nodes and internodes, and in the fact that the 

 leaves and branches sprang only from the nodes, a considerable 

 resemblance exists between the ancient and modern representatives 

 of this group. 



Page 50. Calamites Britannicus, Weiss.* This specimen 

 shows the external surface of the bark of a Calamite, which is very 

 rarely preserved. Two constrictions or nodes are seen, and two 

 internodes. The surface of the internodes is smooth, but ornamented 

 by short grooves, mostly directed transversely. The uppernode bears 

 the scar of a branch. No leaves are seen on this specimen. From the 

 Yorkshire coalfield. Slightly reduced. 



Page. 51. Calamites sp. Transverse section ot a petrified 

 stem of a Calamite. As a rule the casts of Calamite stems are pith- 

 casts, which are formed by the filling up of the hollow pith cavity 

 by mud or sand, which, when set hard, gives us a shale or sandstone 

 cast. The next three photographs show such pith-casts. Where, 

 however, the stem is preserved as a petrifaction, the internal 

 anatomy can be studied. This photograph shows a cross section 

 of such a stem. The clear space in the centre is the pith-cast 

 filling the central, hollow portion of the pith. Part of the pith itself 

 is preserved outside this cast, and next we see a ring of dark, wedge- 

 shaped vascular bundles, the wood, each with a large, circular canal 

 at its inner extremity. Between the bundles thin walled medullary 

 rays are seen. Outside the wood the cortex is visible, which exter- 

 nally is strengthened by a thin layer of bark. The whole structure 

 of the stem recalls that of a modern Horsetail. From the Lancashire 

 coalfield. X about 10. (Photomicrograph by Mr. Tarns.) 



Page 52. Calamites Suckowi, Bronguiart.* A pith-cast show- 

 ing five nodes, and portions of six internodes. In this species 

 the internodes are often broader than long, and the nodes do not 

 bear any branch-scars. The internodes are ridged and grooved 

 longitudinally, as is the case in all Calamitean pith-casts. Usually 

 the ridges and grooves of successive internodes alternate. Below 



