No. 467.] STUDY OF THE SALICACEE. 827 
smaller in the outer limits of the growth ring; 1-to 4-compounded. Medul- 
lary rays narrow but rather prominent and somewhat resinous ; one cell 
wide, numerous and distant upwards of 12 rows of cells. 
Radial— Ray cells straight. Cells (1), the upper and lower walls thin 
and not obviously pitted except in the outer limits of the growth ring; the 
terminal walls straight or curved, and finely pitted. Cells (2), the upper 
and lower walls usually thick and more or less strongly pitted ; the terminal 
walls rather thick and strongly pitted ; the lateral walls with round or spar- 
ingly angled and radially seriate pits. 
Tangential.— Rays rather numerous, resinous, high, narrow, strictly 1- 
seriate. Cells (1) chiefly uniform, narrowly oblong and equal, in a few rays 
becoming broader and oblong, somewhat unequal. Cells (2) not readily 
distinguishable. 
11. P. heterophylla Linn. 
Transverse.— Growth rings medium, rather uniform ; the limiting wood 
parenchyma not very prominent, usually one cell thick and often forming a 
discontinuous zone. Vessels numerous and large, oval or round, often in 
series continuous and compounded with those of the previous year, dimin- 
ishing steadily in size toward the outer face of the growth ring ; chiefly 
single but often 2-, or on the outer face of the growth ring sometimes 3- 
compounded. Medullary rays not very prominent, 1 cell wide, rather 
numerous and distant upwards of 6 or more rarely 10 rows of cells. 
Radial.— Medullary rays non-resinous. : Cells (1), the upper and lower 
walls, as also the terminal walls, usually rather thick and strongly pitted. 
Cells (2), the upper and lower walls somewhat thinner, less strongly pitted ; 
the terminal walls strongly pitted; the lateral walls with round, oval, or 
sparingly angled pits. 
Tangential.— Medullary rays numerous, rather high, non-resinous, nar- 
row, 1 cell wide. Cells (1) chiefly uniform in the same ray, oblong and 
equal, but between different rays varying from narrowly oblong to rather 
broadly oblong. Cells (2) not distinguishable from the first. 
2. Salix. 
Radial.— Ray cells (1) usually low and thick-walled, several times 
longer than high ; the upper and lower and terminal walls commonly pitted. 
Cells (2) often thin-walled, marginal, and interspersed, commonly predom- 
inant, very variable, short, and often several times higher than long ; the 
pits on the lateral walls more definitely angled, forming more extensive and 
finer sieve-plates, and sometimes merging into definite scalariform struc- 
ture. 
Tangential.— Ray cells clearly distinguishable as of two kinds. 
