IOWA ACADEMY OP SCIENCES. 
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colorless parenchyma cells. These primary bundles are enclosed 
by the parenchyma and mestome sheaths. Those of the sec- 
ondary type are entirely closed and surrounded by chlorophyll- 
bearing parenchyma. Third is an intermediate type, open only 
interiorly; the leptome is in contact with the stereome, while 
the hadrome is surrounded by chlorophyll-bearing parenchyma 
cells. These intermediate bundles occur in only two places in 
the leaf, — one is found in the carene and one at the margin of 
the leaf. 
Carene . — The carene -consists of one mestome bundle. A 
large bundle open above and below, i. e., the leptome and 
hadrome are in contact with the stereome. The pitted ducts 
are irregular. The stereome is more abundant above than 
below the bundle. This is true of all the open bundles in this 
species; the leptome is separated from the hadrome by a layer 
of thick-walled parenchyma cells, while the whole bundle is 
enclosed in both parenchyma and mestome sheaths. On one 
side of this primary bundle a secondary bundle occurs; this is 
entirely closed by chlorophyll-bearing parenchyma cells. Lep- 
tome and hadrome are present with a few thick -walled cells 
between them, and the whole enclosed by a mestome sheath. 
On the opposite side of the primary bundles is one of the inter- 
mediate type. 
Stereome . — This occurs on the margin of leaf above and below 
the primary bundles, and above the intermediate bundles. 
Colorless parenchyma is more or less developed below all the 
bundles of the primary type. 
Mesophyll is found between all bundles, surrounding the sec- 
ondary and below the intermediate bundles. It consists of elon- 
gated cells filled with chlorophyll. 
BROMUS SEC-ALINUS. 
(PI. vi, Fig. 2; PL viii, Fig. 9.) 
Epidermis . — In this species, the epidermal cells are large and 
regular on inferior surface with an occasional cell projecting 
outwardly. On the superior surface of the leaf the cells are 
somewhat smaller and of same general shape. The leaf is 
somewhat involute. Small trichomes in the shape of conical 
projections are present on the inferior surface of the mestome 
bundles. Epidermal cells are smaller where it covers the 
primary mestome bundles in this species, as in all studied. 
Stomata present on both surfaces. 
