314 



LYCOPODIUM 



genera Lycopodium (Fig. 179) and Selaginella (Fig. 180). The 

 Quillwort (Isoetes lacmtris, Fig. 178), which occurs submerged 

 in mountain tarns, is a peculiar member of this group, many of 

 whose features recall those of the fossil Clubmosses (Lepido- 

 dendron and Sigillaria, Fig. 177). Fragments of the stems of 



the former with, or often 

 without, the leaves, are 

 very common in the Coal 

 Measures, and are readily 

 identified by their charac- 

 teristic markings (Fig. 

 175, C). 



The small spirally ar- 

 ranged leaves of Lyco- 



,, , podium densely clothe the 



I A stems, which are either 



erect, as in the Fir Club- 

 moss (L. selago), or pros- 

 trate, except for the 

 cone-bearing shoots, as in 

 the Bear's Foot (L. clavatum, 

 Fig. 179, A). The stems, 

 as well as the occasional 

 adventitious roots, exhibit 

 forked branching, and 

 never contain more than a 

 single stele, 1 whose detailed 

 structure is often some- 

 what complex. The sessile 

 leaves are attached by a 

 broad cushion -like base, 

 and are traversed by but 

 a single median vein (Fig. 179, B) ; the same was the case in 

 Lepidodendron , the persistent leaf-cushions affording the dis- 

 tinctive markings above referred to. The British species of 

 Lycopodium are found in moist upland pasture, except for 

 L. inundatum, which occurs in lowland bogs. 



1 A single stele was likewise found in Lepidodendron where, however, it 

 became enveloped by a broad zone of secondary wood and phloem. 



FIG. 177. Restoration of various fossil 

 Clubmosses (Lepidodendron and 

 Sigillaria). (After Grand Eury.) 



