CHAPTER XXI 



HORSETAILS AND CLUBMOSSES 



THE Ferns (Filicales) alone of the three existing groups of 

 Pteridophyta are widely represented at the present day. Not 

 only are they almost ubiquitous in their distribution, but they 

 comprise a large number of families and genera. The Bracken 

 in North Temperate zones, and Gleichenia in the Tropics, illus- 

 trate, moreover, the important role played by Ferns in many 

 types of vegetation. 



The Horsetails (Equisetales) and Clubmosses (Lycopodiales) , 

 on the other hand, which, like the Ferns, have been traced 

 back in the fossil state to very early periods of the earth's history, 

 are now only represented by a few very distinct genera. These 

 groups flourished vigorously, however, at the period when the 

 Coal Measures were laid down ; then they comprised woody 

 plants which, in great part, attained to the dimensions of trees 

 (Fig. 177), at least sixty feet high in the case of Catamites. These 

 features have been lost by the living forms of the present day, 

 which are herbaceous and of small dimensions. It is, indeed, 

 probably correct to regard the remote past as the age of trees 

 and the present rather as that of herbs. 



By contrast with Ferns the leaves of Horsetails and Club- 

 mosses are remarkably small and simple in form, so that the 

 habit of the plant is here determined mainly by the character 

 and extent of branching of the stem (Fig. 174, B and C ; 

 Fig. 180, A). The Horsetails (Equisetum) are switch-plants 

 (Fig. 174, B and C) whose green, longitudinally furrowed, stems 

 bear whorls of brownish scale-leaves fused to form a toothed 

 sheath (SI.) around each node. The branches are likewise 

 whorled (Fig. 174, B), and, since they arise relatively late, have 

 to pierce their way through the bases 'of the fused leaves. The 



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