482 BOTANICAL GAZETTE [DECEMBER 
tangential line made up of several rows of radially flattened wood 
fibers which mark the outer boundary of the late wood. The 
early wood of the next annual ring lies immediately outside of 
this dense tissue, and it begins with a more or less continuous 
row of pores. The portion of the ring formed in the beginning 
of the year’s growth is thus considerably more porous than that 
produced at the end of the season. The pores are slightly less 
numerous and smaller in diameter in the late wood than in the 
early wood, but they are so nearly uniform in size throughout 
the annual rings of growth that with the unaided eye they do 
not materially assist in defining the inner and outer boundaries of 
growth rings. 
The annual rings do not differ in the three sycamores except 
that in the eastern species they are less clearly defined than in the 
other two. The width of these annual layers of growth varies 
considerably. The annual diameter increment of the eastern 
species for trees of about go years of age and growing under average 
soil and site conditions is approximately 0.2 in. per year. On an 
average the western species grow much more slowly. 
PITH RAYS 
_ The numerous broad pith rays constitute the most striking 
character of sycamore wood; they are conspicuous (pl. XXXII, pr ) 
both in the transverse and radial sections. In the distinctness of its 
pith rays sycamore woods have a general resemblance to beech, the 
large pith rays of the latter, however, being less numerous. The 
rays of sycamore wood are very conspicuous in quarter-sawed 
boards, giving the cut surface a “silver grain” effect similar to 
quarter-sawed oak. In tangential or “bastard cut” boards the 
pith rays are least conspicuous, although clearly visible to the 
unaided eye. With the hand magnifier they appear as numerous 
and evenly distributed, short, vertical lines. 
As stated, the size of the pith rays is one of the chief distinguish- 
ing characters of the sycamore woods. In gross structure (as 
seen with the hand lens) the rays are decidedly larger and 
usually darker in the common sycamore than in the other two 
species. 
