422 
ELEMENTS OF GEOLOGY. 
or cicatrices, left after the fall of the fronds. These scars 
resemble those of Caulojyteris. 
1^0 less than 130 species of ferns are enumerated as having 
been obtained from the British coal-stfata, and this number is 
more than doubled if we include the Continental and Amer¬ 
ican species. Even if we make some reduction on the ground 
of varieties which have been mistaken, in the absence of their 
Fig. 451. 
Liviug tree-ferns of different genera. (Ad. Brong.) 
Fig. 450. Tree-fern from Isle of Bourbon.—Fig. 451. Cijathea glauca, Mauritius.— 
Fig. 452. Tree-fern from Brazil. 
fructification, for species, still the result is singular, because 
the whole of Europe affords at present no more than sixty- 
seven indigenous species. 
Lyco^odimQedd — I^epidodendron ,—About forty species of 
fossil plants of the Coal have been referred to this genus, 
more than half of which are found in the British coal-meas¬ 
ures. They consist of cylindrical stems or trunks, covered 
Avith leaf-scars. In their mode of branching, they are always 
dichotomous (see Fig. 454). They belong to the Lycopodia- 
cem^ bearing sporangia and spores similar to those of the liv¬ 
ing representatives of this family (Fig. 457); and although 
most of the Carboniferous species grew to the size of large 
trees, Mr. Carruthers has found by careful measurement that 
the volume of the fossil spores did not exceed that of the re¬ 
cent club-moss, a fact of some geological importance, as it 
may help to explain the facility with which these seeds may 
