470 BOTANICAL GAZETTE [December 



elongation is variable, as is also the height and the depth of the cell, 

 which latter, however, approximates that of the ray with which it is 

 associated. The pitting on the walls is very characteristic, espe- 

 cially in horizontal contact with the parenchyma cell of the ray. 

 Second, the interspersed type of ray tracheid, as shown in fig. 2, 

 where the tracheary cells occur in the midst of the radial prolonga- 

 tion of rays one cell high. They may be found singly, or in groups 

 separated from other cells or groups of cells of similar structure 

 by one or more parenchyma cells. Fig. 2 shows two tracheid 

 cells occurring together with parenchymatous ray cells on either 



Fig. 3. — Radial section (second growth wood) showing most common form in 

 which vertical wood tracheid is bent and prolonged along the ray to act as ray tracheid; 

 note diversity of pitting in walls of tracheary cell. 



side. In these the pitting is very characteristic, especially in the 

 radial end walls. Miss Holden has spoken of such rays as these 

 as "secondary rays." 



X In contrast to the foregoing, the marginal structures on the 

 rays of the wood of second growth 5. washingtoniana show great 

 variation. True ray tracheids in accordance with the previous 

 descriptions do not occur. On the margins of the rays, however, 

 there is a peculiar adaptation in the termination of the vertical 

 wood tracheids directly at the ray, with the development of com- 

 municating pits in the contiguous walls of the tracheids and the 



