154 LEriDODENDREiE. 



in the axil of more or less modified leaves, which may he aggre- 

 gated into strobili, or occupy a similar position to the sterile leaves. 

 In some extinct genera the mature sporangium is enveloped by an 

 integument, and thus was of the nature of a seed. 



The living Lycopods belong to the following genera, of which 

 Lycopodhm (the Club - mosses), Phylloglossum, Psilotnm, and 

 Tmesipteris are isosporous, while Selaginella and Isoetes are 

 heterosporous. In Palaeozoic times this group was a very large 

 and diversified one, and then attained to its maximum development ; 

 the chief geriera being Lepidodendron, LepidopMoios, Sigillaria, 

 and Bothrodendron. 



All these Palaeozoic types are characterised by an arborescent 

 habit, and the power of secondary growth in thickness. 



In the Mesozoic and Tertiary rocks the Lycopods are much less 

 abundant, the genus Lycopodites being the chief representative, 

 including plants more closely resembling the recent genera than 

 the arborescent Palaeozoic types. 



In the Northern Permo-Carboniferous continent the Lycopods 

 formed one of the most important elements in the flora. It is 

 interesting to note that, while this group appears to have been 

 entirely absent from the Southern type of vegetation in India and 

 Australasia, it was well represented in Southern Africa and 

 South America, where Lycopods occur in association with the 

 Glossopteris flora. These Southern Lycopods were, however, all 

 identical generically, and some of them specifically, with those 

 found in Europe, North America, and Northern Asia. All the 

 more important Palaeozoic genera mentioned above have now 

 been recorded from either Southern Africa or South America. 



Family LEPIDODENDRE.E. 



Arborescent Lycopods, dichotomously branched. Stem clothed 

 with leaves or with an armour of persistent, spirally arranged, 

 prominent leaf-bases. Leaf-bases approximate, more rarely distant 

 and separated by bands of bark. The leaf-base consists of a leaf- 

 cushion and a leaf - scar. The leaf - cushions are fusiform or 

 rhomboidal. The leaf -scar varies in shape, but is usually more 

 or less transversely elongate, and bears three prints, the central one 



