FOSSIL PLANTS OF THE CARBONIFEEOUS SYSTEM. 733 



ofi from that part of the primary one which happens to be nearest 

 the secondary rachis to be supplied. 



Fossil plants, allied to Lyoopodiums, also occur in the Coal- 

 measures. Brongniart believes they are more abundant in the ancient 

 beds than in the superior beds of the greater part of the coal for- 

 mation. These have been included under the genera Lycopodites, 

 Selaginites, and Lepidodendron (Ximg, a scale, and dhdgov, a tree), 

 (figs. 911, 912). The last mentioned appear to occupy an intermedi- 

 ate place between Coniferse and Lycopodiacese. Their leaves are 

 arranged in the same manner as some of 

 the Coniferse, and their scars are similar. 

 Their branches bifurcate like Lycopodiacese. 

 They occur in the form of dichotomous 

 trunks, 20 to 45 feet high, with linear or 

 lanceolate leaves (fig. 912), like those of 

 some species of Lycopodium and Eutassa. 

 Schimper enumerates 59 species of Lepido- 

 dendron, all arborescent and carboniferous. 

 The stem consists of a thin cuticle, a double 

 cellular zone, a vascular cylinder, and a pith. 

 The vascular cylinder consists of polygonal 

 tubes marked with lines, while the pith is 

 composed of fusiform cells. The stems are 

 marked with rhomboid and orbicular scale- 

 like scars (fig. 911)i Their cone-Uke firuit 

 occurs in a fossil form, called Lepidostrobus 

 (fig. 913). It consists of a central axis 

 bearing scales, which cover sporangia. In 

 the interior of these there are spores con- 

 sisting of 3 or 4 angular sporules. There 

 is a single sporangium on each scale, and all the sporangia are filled with 

 microspores. In Lepidostrobus we do not meet with two kinds of spores. 



In Triplosporites, another Lycopodiaceous plant, there is a single 

 sporangium on each scale. The sporangia in the upper portion of the 

 cone contain microspores, while those at the lower part have macro- 

 spores, in the same way as occurs in the genus Selaginella (p. 278). 

 riemingites is another fruit of the same kind. It is a cone with a 

 double series of small sporangia on each scale. The sporangia of 

 riemingites occur sometimes abundantly in coal (Trans. Roy. Soc. 

 Edin., xxi. 187). It is conjectured that in some cases the mass of 

 the coal is formed by sporangia of plants allied to Ferns and Lycopods. 

 The various forms of Lepidophyllum are said to be the leaves of 



Fig. 913. Lepidostrobus ornatus, after Lindley and Hutton, from the Bensham coal- 

 seam of tlie Jarrow colliery, showing central axis with leaflets. It is the fructification of a 

 Lepidodendron. 



Pig. 913. 



