No. 467.] STUDY OF THE SALICACEE. 831 
4. S. nigra Marsh. 
Transverse.— Growth rings broad, the inner region of the growth ring 
usually more dense; the limiting wood parenchyma sparingly resinous, in 
1 to 2 rows of cells. Vessels numerous, large, rather broad, and oval, grad- 
ually diminishing in size and number toward the outer region of the growth 
ring and finally becoming few, narrow, and rather small; 1- to 3-com- 
pounded or in the outer portions of the ring often 8-compounded and nar- 
row. Rays rather numerous, not very prominent, very sparingly resinous, 
1 cell wide, and distant upwards of 8 rows of wood cells. 
Radial.— Medullary rays locally resinous. Cells (1), the upper and lower 
walls rather thin and usually not obviously pitted ; the terminal walls chiefly 
thin and devoid of pits. Cells (2), the upper and lower walls thin and devoid 
of pits; the terminal walls strongly but finely pitted ; the pits on the lateral 
walls forming a strong sieve-plate structure. 
Tangential.— Rays very numerous, medium, sparingly resinous, ı-seriate, 
and broad. Cells (1), variable, unequal, oblong and narrow or more often 
broad and oval or squarish; unequal. Cells (2) less resinous, variable but 
chiefly narrowly oblong, unequal, and differing in both height and width. 
5. S. alba Linn. 
Transverse.— Growth rings very broad, the limiting wood parenchyma 
I to 2 cells thick, resinous. Vessels strongly predominant throughout ; 
large, oval, often oblong, chiefly single but often 2- to 3- or more rarely 4- 
compounded ; not diminishing sensibly toward the outer face of the growth 
ring. Medullary rays numerous, somewhat resinous, I cell wide, distant 
upwards of 8 rows of wood cells. 
Radial.— Rays sparingly resinous. Cells (1), the upper and lower walls 
thick, and strongly pitted throughout, the terminal walls generally curved 
and strongly pitted. Cells (2), the upper and lower and terminal walls 
strongly pitted; the pits on the lateral walls forming a strong sieve-plate 
structure; often approximating in height and general character to cells (1). 
Tangential.— Rays resinous, numerous, narrow, medium. Cells (1) uni- 
form in the same ray but variable in different rays, and ranging from nar- 
rowly oblong to oblong; chiefly equal. Cells (2) less resinous, uniform but 
unequal, differing greatly in height. 
6. S. lasiandra Benth. 
Transverse.— Growth rings broad; the limiting zone of un. 
chyma continuous, conspicuous and resinous, I to 2 cells thick. — 
strongly predominant, radially and somewhat tangentially 2- to 5com 
pounded, steadily diminishing in size to the outer limits of the growth ring 
