Supposed Hybrid of the Black and Shingle Oaks 323 



IMBRICARIA 



Transverse (plate XIII, fig. 1; plate XIV, figs. 1, 4). The pith 

 cells are generally roundish, rather loosely packed together, and 

 fairl} uniform in size. The broad pith rays are from three to 

 seven cells in width in the first year's growth and broader in the 

 older stems. The narrow rays, mostly a single cell in width, are 

 poorly defined and inconspicuous. Extending out from between 

 the groups of protoxylem next the pith are rays which begin with 

 a width of three or four cells, but which quickly narrow to the 

 dimensions of the ordinary narrow ray. In older stems secondary 

 broad rays develop by the coalescence of narrow rays.'' In 

 the broad rays the cells are rectangular, narrow, elongated 

 radially, with oblique tangential walls. In the narrow rays the 

 cells are sometimes squarish in the spring wood, and come to be 

 elongated radially in the summer wood. Protoplasmic connections 

 appear rather conspicuously between the pith cells, between the 

 ray cells, and between the two. Wood parenchyma is rather 

 sparingly distributed among the tracheids and wood cells of the 

 spring wood, and occurs in the summer wood as occasional wavy 

 tangential bands. The cells are larger than the wood cells, are 

 thin walled, roundish, and fairly uniform in size. The wood 

 fibers are triangular to septagonal, largely pentagonal, and vary 

 somewhat in size. In the spring wood they are thin walled and 

 are distributed without special grouping among the large vessels 

 and tracheids. In the summer wood they are massed in blocks 

 of considerable size which are penetrated by occasional tracheids, 

 and bounded by the medullary rays and bands of wood paren- 

 chyma. A fairly distinct radial arrangement of the fibers can 

 be made out, which becomes definite with the squarish cells at 

 the outer margin of the sharply defined growth ring. Tracheids 

 are fairly numerous in the spring wood, where they vary consider- 

 ably in size and shape, being irregularly distributed among the 

 wood parenchyma cells and wood fibers between the large vessels. 

 In the summer wood they are less numerous, are circular in form, 

 and are usually found close to the cells of the pith rays. They 

 are thick walled, with numerous oval bordered pits. The vessels 

 are almost wholly confined to the spring wood where they are 



" Eames, Botanical Gazette, vol. xlix, pp. 161-167, 1910. 



