No. 467.] STUDY OF THE SALICACEE. | 825 
Tangential.— Rays very numerous, resinous, medium to high, narrow, 
I-seriate. The cells (1) chiefly uniform, rather narrowly oblong and equal in 
the same ray, but in different rays sometimes varying to broadly oblong. 
Cells (2) not readily distinguishable except by their less resinous contents 
and somewhat more variable form and unequal size, usually giving the ray 
a diminishing terminal width. 
6. P. grandidentata Michx. 
Transverse. — Growth rings narrow, uniform ; the limiting wood paren- 
chyma with thin-walled cells in 1 to 3 rows, often very resinous. Vessels 
numerous throughout the growth ring but usually much smaller near the 
outer limits of the ring; 1-to 4- more rarely 5-compounded. Medullary 
rays prominent but narrow, ı cell wide and distant upwards of 10 or some- 
times 12 rows of cells ; somewhat resinous. 
Radial.— Ray cells straight. Cells (1), the upper and lower walls thin 
and entire or obscurely pitted ; the terminal walls thin, straight, or curved, 
finely pitted. Cells (2), the upper and lower walls rather thin and not obvi- 
ously pitted; the terminal walls often strongly curved, rather thick, and 
conspicuously pitted ; the pits on the lateral walls oval or round in radial 
series. Isodiametric, thin-walled idioblasts, containing each a single crystal 
of calcium oxalate of the quadratic system, often form extensive, longitu- 
dinal series adjacent to vessels. 
Tangential. — Medullary rays numerous, narrow and high, strictly 
I-seriate, resinous. The cells ( 1) chiefly uniform in the same ray and nar- 
rowly oblong, equal; but between different rays varying to oblong. Cells 
(2) not very readily distinguishable, but usually less resinous and often 
variable from narrowly oblong to oval so as to give the same ray a con- 
spicuously unequal width. 
7. P. wislizent Watson. 
Transverse. — Growth rings broad ; the limiting wood parenchyma spar- 
ingly resinous in 1 to 3 rows. Vessels at first, predominant, gradually 
diminishing in size and number toward the outer limits of the growth 
ring ; 1- to 3-, more rarely 4- to 5-compounded. Medullary rays prominent, 
narrow, one cell wide, distant upwards of 10 rows of cells, numerous, 
sparingly resinous. i 
Rie — Ray cells straight, equal to about 14 wood cells but becoming 
very short toward the outer limits of the growth ring. Cells (1), the upper 
and lower and terminal walls rather thin, rather obscurely and finely pitted ; 
the pits on all the walls becoming much more prominent in the outer region 
of the growth ring. Cells (2), the upper, lower, and termina walls not et 
different from (1); the pits on the lateral walls forming a coarse sieve-pla 
Structure. 
