834 THE AMERICAN NATURALIST. Vor. XXXIX. 
resinous ; the structure rather dense throughout. Vessels not predominant ; 
at first very numerous and very resinous, quickly diminishing in number 
and thence constantly diminishing in size and number, and always distant, 
to the outer face of the growth ring; rather small, oval, sparingly 2- or 
more rarely upwards of 4-compounded ; everywhere numerous. Resinous 
wood parenchyma cells numerous throughout ; associated with vessels and 
scattering throughout the growth ring, often forming more or less definite 
and extensive tracts. Medullary rays very numerous, resinous, I cell wide, 
distant upwards of 10 rows of cells. 
Radial.— Ray cells very resinous. Cells (1), the terminal walls very 
thick and very strongly pitted ; the upper and lower walls sparingly if at all 
pitted except in the later portions of the growth ring. Cells (2), often 
predominant ; the upper and lower walls thin and not pitted except in the 
later portions of the growth ring; the terminal walls strongly pitted ; the 
pits on the lateral walls forming a coarse sieve-plate structure. 
Tangential.— Rays very numerous, medium, narrow, resinous. Cells (1) 
uniform, oval, and chiefly equal throughout. Cells (2) variable, oblong, 
often very narrow and unequal, often several times higher than broad, the 
walls commonly thinner. 
12. S. lasiolepis Torr. 
Transverse— Growth rings broad; the limiting wood parenchyma 1 to 
4 cells thick, sparingly resinous. Vessels at first not strongly predominant ; 
oval or oblong, steadily diminishing in size and finally much reduced ; 
chiefly single throughout, but sparingly 2- to 3-compounded. Medullary 
rays numerous, locally resinous, 1 to 2 cells wide, distant upwards of 6 rows 
of wood cells. | 
Radial. — Medullary rays resinous. Cells (1), the upper and lower walls 
sparingly and unequally pitted, often devoid of pits; the terminal walls 
strongly but finely pitted. Cells (2), the upper and lower walls chiefly 
rather thin and devoid of pits; the terminal walls strongly pitted ; the pits 
on the lateral walls forming a coarse sieve-plate structure often coalescing 
into a Coarse scalariform structure. 
Tangential. — Rays very numerous, medium, resinous, I- to 2-seriate. 
Cells (1) variable, oval to oblong, and conspicuously unequal. Cells (2) 
less resinous, variable, and unequal, often high. 
13. S. sessilifolia Nutt. 
Transverse — Growth rings broad ; the limiting wood parenchyma 1 to 
2 rows of cells broad, occasionally resinous and confluent with resinous 
wood parenchyma in the adjacent spring wood. Vessels numerous and 
predominant throughout ; radially oval and variable in size ; I- to 2-, more 
