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IOWA ACADEMY OF SCIENCES. 
bundle, smaller than the mid-bundle but open superiorly and 
inf eriorly, i. e. , the leptome and hadrome are in contact with 
the stereome, but this bundle differs from the first described, in 
that it has interiorly only a single row of stereome running 
from the bundle to the epidermal cells, while in the first one 
there is a large amount of stereome on inferior surface. The 
stereome beneath this second bundle conforms with that found 
in the other primary bundles of this species. All these primary 
bundles are surrounded by two sheaths: an outer, thin- walled 
colorless row of cells, the parenchyma sheath and inside] this a 
thick- walled row of cells, sometimes incomplete, the mestome 
sheath. The bundle on the other side of the central bundle is 
one of the secondary type. No stereome occurs in connection 
with these bundles; they are entirely closed, that is, wholly 
surrounded by chlorophyll- be ar ing parenchyma . These bundles 
are enclosed by a mestome sheath but the parenchyma sheath 
is absent. The leptome and hadrome fill the entire space inside 
the mestome sheath unless possibly a few thick- walled cells 
between them. 
Stereome . — This occurs only above and below the primary 
bundles, and on the margins of the leaf. 
Colorless parenchyma occurs below the stereome of all pri- 
mary bundles, and forms a sheath for the 'whole primary mes- 
tome bundle. 
Mesophyll . — This surrounds not only the secondary bundles 
but occurs between all the primary and secondary bundles. 
BROMUS INERMIS. 
(PI. V, Fig. 4; PL vii, Fig. 10.) 
Epidermis.— ixi this species we find large, regular, and well 
developed epidermal cells with a thick cuticle; the cells are 
smaller and the cuticle thicker under and above the mestome 
bundles than elsewhere. The epidermal cells are slightly 
longer on superior surface of leaf than on inferior surface. 
Trlchomes absent. Stomata occur on both surfaces of leaf, but 
especially between the buliiform cells. 
Bulliform cells . — These are large, varying in number from 
three to seven, only present on superior surface of the leaf. 
Mestome bundles . — These number thirty-five, and are of three 
types, as in some specimens of Bromus asper. First, those 
of the primary type; these are open both on anterior and 
inferior surfaces of the leaf, i. e., the leptome is in direct con- 
tact with the stereome and the hadrome, separated from it only by 
