IOWA ACADEMY OF SCIENCES. 
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P. dumetorum var. scandens, Gray. 
Figure 3. plate vii. 
In this species the '‘palisade” cells are long with j^apillate 
projections, giving the cells an irregular outline. The cell 
avity is long and narrow, with quite long, slender canals, 
extending from sides; at the upper end of the cell the cavity 
divides into two branches which terminate in the end of the cell; 
the cell and the cell-cavity is light brown in color, the cavity 
being somewhat darker than the rest of the cell. In the ‘ ‘ sub- 
palisade ” portion but two layers of cells occur. The endosperm 
is composed of cells much broader than those of P. Virginianum 
and are quite irregular in form. Measurements — achenium 
142u; “ palisade” cells, 122. lu; “sub-palisade,” 13. 2u; papillate 
projection, 9.9u. 
P. Hydropiper, L. 
Figure 1, plate ix. 
In specimens of P. Hydropiper the “palisade” cells are long 
and narrow, very irregular and truncate at ends. The cell- 
cavity is very narrow and extends the whole length of the cell. 
The cavity has minute canals which extend out from sides: the 
cavity also truncate at ends. The cell is colored light brown 
while the cavity is deeper in color. The “palisade” cells resem- 
ble very much those of P. Virginianum. The “sub-palisade,” 
however, are much smaller with more numerous indistinct layers, 
there being at least six layers well defined. The endosperm 
cells also are small and quite irregular. Measurements — ache- 
nium, 132u; “palisade” cells, 92. 4u; “sub-palisade,” 39. 6u. 
P. erectum, L. 
Figure 5, plate vii. 
In this species the “palisade” cells are much broader than in 
any other Polygonum studied. The cells have irregular papil- 
late projections as in P. dumetorum var. scandens. The cell-cavity 
is narrow with long canals extending from it; the cavity branches 
are forked. In P. erectum the Avhole cell is of a light brown 
color, while the cavity is colorless. The ‘ ‘ sub-palisade ” portion 
consists of two layers of isodiametric cells. The endosperm has 
long, narrow, regular cells. Measurements — achenium, 82. 5u, 
“palisade,” cells, 60u; “sub-palisade,” 22. 5u; papillate projec- 
tion, 3.3u. 
P. Persicaria, L. 
Figure 6, plate viii. 
In this species the “palisade” cells are long, narrow and trun- 
cate. The cell cavity extends the whole length of the cell; at the 
