THE ANATOMY OF WOODY PLANTS 



addition there can be made out other small cells which are not so 

 markedly thickened. Finally, the tissues include cells with walls 

 which are distinctly thin the wood parenchyma. In the case of 

 the cells with moderately thickened walls, where the bottom (or 

 top) is included in the plane of section, scalariform thickenings can 

 readily be distinguished. The thin-walled elements, when the lower 



FIG. 30. Longitudinal section of the primary wood of a lepidodendrid. 

 planation in the text. 



Ex- 



or upper wall is exposed in the preparation, show it to be without 

 scalariform sculpture. 



A highly important light is thrown on the facts recorded at 

 the end of the preceding paragraph by the longitudinal section of 

 the same primary wood exhibited in Fig. 30. Here may be seen 

 a number of long structures with thick walls and scalariform 

 sculpture. These are tracheids of the primary wood. Here and 

 there may be distinguished other structures of similar length, 



