XVj LEPIDODENDRON 95 



apart and the original surface-features become obliterated by 

 vertical cracks and by the exfoliation of the superficial tissues^. 



Some species of Lepidodendron produced branches charac- 

 terised by spiral or vertical series of scars ; these in older shoots 

 were replaced by depressions having a diameter of several inches 

 and comparable in appearance, as also perhaps in manner of 

 formation, with the scars left on the stem of a Kauri Pine 

 (Agathis australisY on the abscission of lateral branches by a 

 natural process. These shoots, known as Ulodendron, are 

 described in a subsequent section. (Page 128.) 



A fully-grown Lepidodendron must have been an impressive 

 tree, probably of sombre colour, relieved by the encircling felt of 

 green needles on the young pendulous twigs. The leaves of 

 some species were similar to those of a fir while in others they 

 resembled the filiform needles of the Himalayan Pine {Pinus 

 longifolia). The occasional presence of delicate hyphae in the 

 tissues of Lepidodendron demonstrates susceptibility to fungal 

 pests. 



Architecturally, if one may use the term, Lepidodendron 

 owed its power of resistance to the bending force of the wind 

 to its stout outer bark formed of thick-walled elements produced 

 by the activity of a cylinder of cortical meristem (figs. 148, 172, 

 etc.). The vascular axis, of insignificant diameter in proportion 

 to the size of the stem (figs. 152, 153, 172, 181, A), must have 

 played a subordinate part, from a mechanical point of view, as 

 compared with the solid mass of wood of a Pine or an Oak. 



Within the compass of a text-book it is impossible, even if it 

 were desirable, to include an account of the majority of the 

 species of the widely distributed Palaeozoic genus Lepidodendron. 

 In spite of the great number of known species of this common 

 member of Carboniferous floras, our knowledge of the type as a 

 whole is deficient in many points, and such information as we 

 possess needs systematising and extending by comparative 

 treatment based on a re -examination of available data. 



In order to appreciate the meaning of certain external 



' A good example of an old Lepidodendron stem (L. aculeatum) is figured by 

 Zalessky (04) PI. i. fig. 3. 



