156 



ANCIENT PLANTS 



Fig. 114. Sphenophyllum, Transverse Section with Secondary Wood w. At c the 

 cork formation is to be seen. (Microphoto.) 



out radially through the wood, such as are found in all 

 other zones of secondary wood, and in this arrange- 

 ment of soft tissue the plants are unique. 



Beyond the wood was a zone 

 of soft tissue and phloem, which 

 is not often preserved, while out- 

 side that was the cork, which 

 added to the cortical tissues as 

 the stem grew (see fig. 114, c). 

 Petrified material of leaves 

 and roots is rare, and both are 

 chiefly known through the work 

 of the French palaeobotanist 

 Renault. The leaves are chiefly 

 bands of sclerized strengthening 

 the structure of aerial, not 



Fig. 115. Group of Wood Cells 

 w, showing their shape and the 

 small soft - walled cells at the 

 angles between them p 



remarkable for the 



tissue, and generally had 



submerged leaves. The roots were simple in structure, 



