296 PITYEAE [CH. 



tracheids (fig. 490, A). In the piece of stem shown in the figure 

 the breadth of the wood from the flattened and crushed pith to 

 the broken outer edge is 6 cm. The medullary rays are numerous, 

 uniseriate, rarely 2 cells in breadth; the pits on the radial walls 

 of the ray-cells, 7 10 in the field, are apparently simple, oval, 

 and oblique : the rays are generally 3 4 cells in depth but may 

 be deeper. There are 1 3 rows of hexagonal alternate rows of 

 pits on the radial walls of the tracheids. The primary xylem 

 consists of groups, varying in size and sometimes reduced to a 

 very few elements, in contact with the secondary xylem, usually 

 though probably not invariably endarch. In the two narrow 

 radially elongated and partially destroyed primary strands shown 

 in fig. 490, B, the protoxylem, px, is on the inner edge. The 

 leaf-trace passes through the secondary wood as a single strand. 



FIG. 490. Mesopitys Tchihatcheffi. A, transverse section showing rings of 

 growth in the wood. B, primary xylem with protoxylem, px, and the 

 edge of the secondary xylem, x 2 . (Kidston collection, 2156.) 



In the section reproduced in fig. 490, A, the crushed and flattened 

 pith measures 9 by 2 mm. ; it consists of thin-walled parenchyma 

 with a few scattered thicker- walled cells. 



Nothing is known as to the structure of the cortical tissue or 

 leaves. 



Antarcticoxylon. Seward. 



Antarcticoxylon Priestleyi Seward. The specimen on which 

 this genus was founded was discovered by Mr Raymond Priestley 1 

 in a boulder, probably derived from the Upper Beacon sandstone, 



1 Seward (14) p. 17, Pis. iv. vnt 



