An important section of the carboniferous plants is embraced under the generic name of _Calamites_. They had smooth jointed stems, like reeds, and terminated beneath in an obtuse curved point (Fig. 8), from which there sprang broad leaflets or rather rootlets. After many years of research our knowledge of these plants is still very scanty. Some of them have exhibited a highly-organized internal structure, from which it appears that they consisted--first, of a soft central cellular pith; second, of a thick layer of woody tissue; and third, an external cylinder of strong bark, ribbed longitudinally, and furrowed transversely. They have been ranked with the common horse-tail of our ponds, but they would rather appear to belong to a higher family. The breadth of the stem is very various, some specimens being a foot or more in diameter, others scarcely half an inch. From the discoveries of Professor Williamson and Mr. Binny of Manchester, it seems not unlikely that what we call calamites may be really the inner core of a plant not yet named, just as a set of fossils were long called _sternbergiæ_, before they were discovered to be really the pith of coniferous trees. With regard to the branches of the calamites, Brongniart's conjecture may be true, that they exist among the group of plants called _asterophyllites_. It is not unlikely that many dissimilar plants have been grouped together as calamites, and, on the other hand, that plants allied to the typical species have been thrown into separate genera. For it requires but a slight acquaintance with the vegetable kingdom to know how many forms analogous parts of the same plant may assume, and how impossible it would often be to guess the real relationship of such varieties if they were not found growing together on one plant. [Illustration: Fig. 8. Terminal portion of a calamite stem.] [Illustration: Fig. 9.[18]] [Footnote 18: The fossil given in Fig. 9 is named by Lindley (_Foss. Flo._ t. 15, 16), _Calamites nodosus_. He admits, however, that it was not found in actual contact with a calamite stem. It has exactly the contour of an asterophyllite, and might, perhaps, be referred to that genus. It is inserted here that the reader may see the general form of the asterophyllites, and the close relationship that subsists between these plants and the calamites.]