XXXIl] 



PROTOPITYS 



211 



form of the bordered pits on the radial walls of the tracheids 

 (fig. 462, D). The centre of the stem is occupied by a parenchy- 

 matous pith, elliptical in transverse section, enclosed by a band 



be- 





I 



CD 











no 



FIG. 462. Protopitys Buchiana. A, B. Central region of the stem showing 

 the pith, the primary xylem (black in fig. A) and (A) the inner part of the 

 secondary xylem; a, shoulders of xylem at the leaf -gaps; It leaf - trace ; 

 px protoxylem. C. Secondary, a; 2 , and primary xylem, x 1 . D. Radial 

 longitudinal section of the secondary xylem. E. Scalariform tracheid of the 

 primary xylem. F. Pits on the medullary-ray cells. (After Solms-Laubach.) 



of primary xylem composed of large polygonal tracheids (fig. 462, 

 C, x l ) characterised by a delicate scalariform pitting on all their 

 walls (fig. 462, E). The primary xylem forms a narrow layer on 

 the sides of the ellipse, 1 3 elements broad (fig. 462, A, B), but 



142 



