PLAXTS OF THE COAL. 



367 



found in great abundance, and known under the name of Lepidostrobus 

 (scale - cone), has shown that they bear in the axils of their scales 

 spores like club - mosses, 

 and not seeds like coni- 

 fers. Also, like club-moss- 

 es, there are in these 

 plants two kinds of spores* 

 — microspores and macro- 

 spores. This would again 

 ally them with conifers, 

 for these organs may be 

 said to represent the sta- 

 mens and pistils of higher 

 plants (Fig. 497). The ex- 

 ternal appearance and in- 

 florescence, therefore, in- 

 dicate that they are Lyco- 

 pods, with very strong 

 coniferous affinities. 



This conclusion is en- 

 tirely borne out by the 

 internal structure. Fig. 

 498 represents an ideal 

 cross and longitudinal sec- 

 tion of the stem of a Lep- 

 idodendron. It is seen 

 that the stem consists of 

 a dense outer bark or rind, 

 inclosing a great mass of 

 loose cellular tissue or in- 

 ner bark, through the center of which runs a comparatively small fibro- 

 vascular cylinder, with very distinct pith. Bundles go from the cylin- 

 der outward to form the venation of 

 the leaves. Xow, the structure of a 

 club-moss is almost the same, except 

 that the fibro- vascular cylinder is solid, 

 and there is, therefore, no pith. The 

 presence in Lepidodendron of a dis- 

 tinct pith is an important character, 

 placing it far above modern Lycopods, 

 and allying it most decidedly with Ex- 

 ogens. 



Fig 



-Lepidodendron compared with Club-Moss: a. club- 

 moss; b, b'. scales enlarged; c, microspores; d, macro- 

 spores; a 1 , lepidostrobus; y and z, the scales containing 

 spores; m, microspores; n, macrospores (after Balfour). 



Fig 



Ideal Section of a Lepidoden- 

 dron: a. pith; b. vascular cylinder: c, 

 inner bark; d, rind; e, bases "of leaves; 

 /, vascular threads going to the leaves. 



* Williamson, Nature, vol. viii, p. 498. 



