LEPIDODENDRON 149 



to the two lateral prints on the leaf-scar, called the 

 parichnos (cf. Fig. 62). This structure is common to 

 the Lepidodendreae in general. 



We have so far considered the anatomy of the stem 

 in its primary condition ; in most of the specimens the 

 structure is modified by the appearance of secondary 

 tissues, namely, of periderm in the outer cortex, and of 

 new wood and bast around the stele. In L. selaginoides 

 even the smallest twigs found (which, however, are 

 not usually less than 1 cm. in diameter) may show 

 both these new formations, while in some of the other 

 species, as we have seen, the secondary wood and bast 

 appear to have been limited to the main stem and its 

 principal branches. 



The periderm began to appear early ; in some of 

 the younger specimens its first origin can be traced. 

 It was developed from a zone of cells of the outer 

 cortex, lying immediately within the leaf-bases, between 

 which it was only separated by a few cells from the 

 outer surface of the stem. This zone of tissue became 

 meristematic ; its elements divided tangentially, and 

 acted as a phellogen, producing a very large quantity of 

 secondary cortical tissue (see Fig. 5 9, pd, and compare 

 Fig- S8)- There has been some difference of opinion as 

 to the position of the phellogen in the older specimens, 

 but there is now little doubt that it lay in the outer 

 part of the secondary zone, so that the larger portion of 

 the new tissue was produced on its inner side, and a 

 smaller portion towards the exterior. Thus the greater 

 part of the secondary cortical zone, as it was produced 

 on the inside of the generative layer, is to be regarded 

 as phelloderm. Whether the smaller outer portion 



