208 



THE ANATOMY OF WOODY PLANTS 



low magnification shown in the photomicrograph the inner zone 

 of the transfusion sheath appears merely as a dark boundary sur- 

 rounding the fibrovascular bundle proper. The conducting strand 

 of the leaf is represented by the xylem alone, the phloem having 

 disappeared during fossilization. In Fig. 155 the central region of 

 the foregoing is represented under a higher degree of magnification. 



FIG. 155. Portion of leaf of Prepinns statenensis, more highly magnified 



The tracheary character of the transfusion sheath can now clearly 

 be discerned, as well as the fact that it contains no cells of the 

 nature of parenchyma. The narrowness of the cells constituting the 

 inner transfusion sheath is also now quite apparent. In Fig. 156 

 are shown the various structures of the fibrovascular bundles lon- 

 gitudinally and on a still higher scale of magnification. The outer 

 transfusion sheath is composed of elements with distinct and 

 rather large bordered pits which abut inwardly on the narrow 

 thick-walled cells of the inner transfusion sheath, in turn connected 



