116 



LYCOPODIALES 



[CH. 



by their darker colour from the bulk of the parenchymatous 

 tissue d. 



This section also illustrates another characteristic feature of 

 Lepidodendron, namely the presence of a ligule and a ligular 

 pit: the former is represented by a carbonised patch of tissue and 

 the latter extends from the surface of the cushion at b, just 

 above the leaf-scar, almost to the level of the leaf-trace, It A 

 comparison of this section with figs. 146 and 147 will make 

 clear the relation of the several parts of the cushion and leaf-scar. 



The gaps gg, seen in fig. 148, A and B, mark the position of 



Fig. 150. Lepidodendron vasculare. Leaf-cushions in longitudinal section, 

 (From a specimen in Dr Eidston'a Collection.) 



the delicate meristematic zone or phellogen which arises close 

 to the bases of the leaf-cushions; the phellogen has already pro- 

 duced a few rows of radially disposed elements, represented by 

 short radial lines in the drawing, which constitute secondary 

 cortical tissue. 



In older shoots the amount of the secondary cortical 

 tissue developed on the inner side of the phellogen is consider- 

 able (cf figs. 152, 153). 



