8 WATSON, Two Species of Lepidodendron Harcourtii. 



(Hick, '92), (Weiss, :02). This meristemic condition is 

 most marked at the inner edge of the middle cortex, and 

 has given rise to a radially arranged tissue of an irregular 

 description {Fig. 2, Plate T). This zone also occurs in 

 L. vasculare, Binney, where it is described by Hovelacque 

 as "La zone rayonnee de l'ecorce interne" (Hovelacque, '92). 

 This meristemic middle cortex is very characteristic of the 

 Lepidodendraceae, and has been described in many 

 species. 



In L Hickii this belt is 4 mm. wide in a stem 

 23 mm. in diameter. 



The condition of preservation does not warrant 

 further remarks. 



(5) Outer cortex 



In the series A 169, 170, and 171 (the only sections 

 in which the middle cortex is preserved), there is a sudden 

 change from the large-celled loose tissue of the middle 

 cortex to a firmer tissue, composed of smaller, thicker- 

 walled, and somewhat tangentially elongate cells. 



The cells of the inner part of the outer cortex are 

 slightly elongated vertically, as seen in radial sections, 

 and in some sections seem to have extremely thin walls. 

 {Fig. 1, Plate I.) 



This fact is noted by Williamson, and must have 

 some significance. I was at first inclined to regard it as 

 due to an accident of preservation, but as it occurs only 

 in those sections in which histological details are good, I 

 now think that it may be natural. 



These cells are seen in transverse section to pass 

 imperceptibly into others of similar shape and dimensions, 

 which have thick walls. 



These cells are really slightly longer than the thin- 

 walled cells, but otherwise do not differ from them. 



