i 3 6 STUDIES IN FOSSIL BOTANY 



admirable account of the anatomy. 1 Subsequent 

 investigations, especially those of Williamson and 

 Bertrand, aided by the discovery of a few additional 

 specimens, have rendered Lepidodendron Harcourtii 

 one of the best known among fossil stems. Mr. 

 Watson regards this species as a Lepidophloios. The 

 largest specimen hitherto found has a diameter of over 

 8 cm. (not counting the leaf-bases), while its stele, 

 or rather the wood, which is alone perfect, is rather 

 more than a centimetre in diameter. The wood forms 

 a broad continuous ring, enclosing a parenchymatous 

 pith (see Fig. 56). The outer edge of the wood is 

 crenulated, having a large number of prominent angles, 

 with furrows between them. It is at the prominent 

 angles that the narrow spiral tracheides are placed ; 

 all the interior of the wood is made up of uniform, 

 scalariform elements. Hence it is evident that the 

 whole ring of xylem was centripetally formed, the 

 development having started at the external angles. It 

 appears from M. Bertrand's researches that these angles 

 formed a prominent network on the surface of the 

 woody cylinder ; from the lower corners of the meshes 

 the leaf-trace bundles, or rather their xylem-strands, 

 passed out. The attachment of the strands was at the 

 sides of the tracheal prominences, and not at their 

 extreme points. The phloem, of which the preservation 

 is very imperfect, appears to have formed a narrow 

 continuous band round the wood (see Fig. 56, B). 



The leaf- traces passed very gradually outwards 

 through the cortex to the leaves, one bundle entering 

 each leaf. Hence a large number of the outgoing 



1 Histoire des vtgttaux fossile, vol. ii. 1837. 



