cena 
NortH Haven Sand Prarns 593 
are small over the ridges but large in the grooves and probably 
function as bulliform cells. Stomata occur in the center of each 
groove. Central portion between the vascular bundles is com- 
posed of large pith-cells. Certain cells or vessels, as in the leaf, 
contain a reddish or brown substance. These are called tannin 
cells by Holm, who has figured the stem in transverse section and 
described in detail the structure of the whole plant of this as well 
as of other North American species included by him in the same 
genus (/imbristylis).* 
Carex PennsyLvanica.— Leaf is conduplicate on drying. 
Epidermis consists of small colorless cells larger on upper than on 
lower surface, and much enlarged over the keel, probably having 
the function of bulliform cells; outer walls are thick while the 
partition walls between the cells are thin. There are eleven mes- 
tome bundles, five on each side of the median one, which is 
slightly larger than the other mestome bundles, and is provided 
with a sheath of small parenchyma-cells replaced on the upper 
side by sclerenchyma-cells and on the lower by a large strand of 
stereome which forms the keel. The mestome bundles have 
sheaths of small parenchyma-cells and six of them are reinforced 
by strands of stereome both above and below. Between each pair 
of bundles (five on each side of keel) is a strand of large colorless 
thin-walled cells (parenchymatous tissue) which is probably for 
the storage of water.+ Stomata occur on lower surface. 
Carex MuHLensercit. — Epidermal layer of upper surface is 
composed of rather large colorless cells, uniform in size except 
where partially interrupted over some of the stereome strands op- 
posite the mestome bundles. The cells of the lower epidermis 
are much smaller. The bundles are small and the material 
studied had one bundle in the keel and nine on each side, making 
nineteen in all. Subepidermal strands of stereome occur on the 
keel, and above and below some but not all of the mestome 
bundles. Each bundle is enclosed in a green parenchyma sheath 
inside of which is a stereome sheath with cell lumina nearly closed. 
Between the mestome bundles are very large strands of water- 
eats 
*Holm, T. Am. Jour. Sei. IV. 7: 435-450, f 7-74. 1899. 
t Beal, W. J. The bulliform or hygroscopic cells of grasses and sedges compared. 
Bot. Gaz. 11: 321-326, f. 20. pl. 10. 1886. 
