The Biology of Polyporus Pargamenus Fries 115 
branching toward the periphery of the growth ring. The 
pith-rays are exceedingly numerous and vary in size from 
those too small to see with the unaided eye to great broad 
ones. 
Microscopically the wood of the chestnut oak is seen to 
consist of (a) hoth uniseriate and multiseriate pith-rays, 
(b) pitted vessels, (¢) metatracheal zonate parenchyma with 
simple pits, and (d) wood prosenchyma of two distinet types, 
one having thin walls and bordered pits, and the other having 
thick walls and simple pits.” The pith-rays are exceedingly 
numerous and constitute about one-fifth of the cellular sub- 
stance of the wood. Large pith-rays are often from twenty 
to thirty cells wide and from three to six times as high, and 
appear as long, well-defined lines in transverse sections. The 
pith-ray cells occur in from one to many rows closely packed 
together. Individually they are arranged end to end with 
their long axes in a radial direction. In a transverse section 
these radial rows of parenchyma cells appear as narrow but 
more or less distinct lnes, the larger ones extending from 
the pith to the periphery of the stem. Where these cells 
are in contact with one another or with wood parenchyma 
fibers the pits are simple, but if they le next to the vessels 
or tracheids the portion of the converging pits in the vessel 
walls is bordered, and that of the ray éclle is simple. 
The vessels or trachex make up chiefly the inner and more 
porous part of the growth ring. In the early wood they are 
round or elliptical and from 2—5 rows deep. Small vessels 
in the late wood are often polygonal and sometimes so 
small that their diameters hardly exceed those of the wood 
parenchyma elements. Radial rows of small vessels, which 
oceur in the late wood, are wavy or slightly branched and 
surrounded by numerous wood parenchyma cells which often 
form narrow ‘tangential bands. The vessels are composed of 
comparatively queen -walled tube-like segments arranged longi- 
tudinally end to end, the cavities of the vessels communicate 
* The description of the anatomical structure of this wood is based 
partially upon that given by Sudworth and Mell (1911, pp. 15-21; 
38-39). 
