120 



LYCOPODIALES 



[CH. 



cushions; it consists largely of secondary cortex composed of 

 radially disposed phelloderm cells and tangentially placed 

 secretory strands (represented by the discontinuous black lines 

 in the drawing) : the dotted region in the central part of the 

 axis is composed of primary cortical parenchyma, and the two 

 spaces surrounding the steles contain portions of the lacunar 

 middle cortex. Each stele posseses a narrow crescentic zone 



Fig. 153. Lepidodendron vasculare. 

 (From a specimen (16 x 7-5 cm.) in the Manchester Museum.) 



of secondary xylem ; the amount is greater in the case of the 

 right-hand stele, of which a small piece is shown on a larger 

 scale ; the striking contrast in size between the outer and more 

 internal secondary tracheae is no doubt the expression of some 

 unfavourable condition of growth. The position of the secretory 

 zone beyond the secondary xylem is shown at sc, fig. 152, A. 



