THE CARBONIFEROUS AND PERMIAN FLORAS. 489 



of plants, and also of securing their foot-hold by numerous 

 cord-like roots proceeding from various heights on the lower 

 part of the stem. The fruit was a long cone or spike, bearing 

 spore-cases under scales" (Dawson, Acadian Geology, p. 441). 

 Besides the true Calamites, the Carboniferous Rocks have also 

 yielded the remains of the genus Equisetites, which differed 

 from the Calamites, and agrees with the existing Horse-tails 

 in having sheaths at the joints. 



Calamites often attain a comparatively gigantic size twenty 

 feet or more in length ; and though they generally occur as 

 prostrate and flattened stems, they are not uncommonly found 

 in an erect and uncompressed condition, standing as they grew. 

 The fossils known as Asterophyllites have been referred to 

 Calamites, of which they were at one time supposed to consti- 

 tute the foliage ; but this opinion has been shown to be pro- 

 bably incorrect. 



c. Calamodendron. A good deal of the confusion which has 

 prevailed as to the true nature of Calamites appears to have 

 arisen out of the problematic fossils now generally referred to 

 the genus Calamodendron. As ordinarily found, Calamodendra 

 present themselves in the form of jointed and longitudinally- 

 ribbed cylindrical steins, which are hardly separable from 

 Calamites, except that they show no " areoles," or points 

 whence leaves or branchlets have been given off. From the 

 examination, however, of complete specimens, it has been 

 shown that Calamodendron, as thus constituted, is really nothing 

 more than the cast of the pith or medullary cavity of a com- 

 plex woody stem, thus resembling in its nature the fossils 

 known as Sternbergia. Round the internal axis thus consti- 

 tuted there is found in perfect examples a thick woody envel- 

 ope, composed of ligneous wedges arranged concentrically and 

 separated by intervening tracts of cellular tissue (or " medul- 

 lary rays "). The external surface of the stem is not known, 

 but the woody wedges are stated to consist of " elongated 

 cells, and porous, discigerous, or pseudo-scalariform tissue." 

 The affinities of Calamodendron are uncertain. It is regarded 

 by different authorities as belonging to the Gymnospermous 

 Exogens or to the Acrogens, or as a connecting form between 

 these groups. In any case, it is necessary to distinguish very 

 carefully between Calamodendron and Calamites, the latter 

 being clearly separated by the absence of a woody envelope, 

 and the presence of whorled leaves or branchlets at the arti- 

 culations of the stem. 



d. Lepidodendroids. Under this head we have to consider 

 the genera Lepidodendron and Lepidophloios, generally regarded 



