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cross-section are approximately square or oblong, those in the summer 
wood being much thickened, leaving an irregular-shaped opening. The 
thickness varies from .00454 mim. in the spring wood to .0106 mim. in the 
summer wood. The length and width of the tracheides also vary, those 
in the spring wood being 6.444 mm. in length by .05606 mm. in diameter, 
those in the summer wood being 6,735 mm. by .033388 mm., being very 
slightly longer but decreased considerably in diameter, the decrease in 
width being accompanied by a greatly increased thickness. These figures 
are taken from the early spring and the late summer tracheides. 
The resin ducts occur singly in both the spring and summer zones. 
The medullary rays are somewhat obscure, one row of cells in width 
and 2 to 17 cells in height, except those which contain resin ducts, which 
widen and have a greater height. 
In the longitudinal sections, the walls show striations which are fairly 
prominent, but have very little bowing apart of the walls. 
Pinus palustris requires a drained soil in which to grow, its seed 
years occur at longer intervals, and thus it has a more limited distribu- 
tion than P. taeda. It also has a lesser height and diameter, but has a 
finer grain, and greater weight. The zones of the spring and summer 
wood are distinct from each other, showing in well-marked lines, the 
summer wood appearing oily and compact as against the lighter line of 
the spring wood. The summer zone varies from about one-third to one- 
half of the annual ring. The two zones are so distinct that unless the 
thickness of the walls be noted carefully, the only difference between the 
limits of the summer wood is that the first growth shows an irregular line, 
whereas, the end of the zone for the year’s growth forms a clean-cut ring. 
The tracheides in transverse section are approximately square or ob- 
long, With approximately round or elliptic openings left in the summer 
wood. Those in the spring wood average 4.4555 mm. in length by .04356 
mm. in diameter, and the walls .00643 mm. in thickness. The summer 
tracheides average 4.8533 mm. in length by .0409 mm. in diameter, and 
the walls .01363 mim. in thickness. There is only a slight difference between 
the tracheides of the spring and summer zones in length and diameter, but 
the thickness of the walls is more than doubled. 
The resin ducts occur singly, near to, and in, the summer wood. 
The medullary rays are conspicuous, being one row of cells, rarely 
more, in width. They vary from 2 to 28 cells in height, except those con- 
taining resin ducts, which are much larger. 
