120 
IOWA ACADEMY OP SCIENCES. 
parenchyma enclose the leptome and hadrome. They alternate 
with the primary bundles, except at the margins of the leaf, 
when three occur in succession on one side of the large pri- 
mary bundle in the carene. Two of the secondary bundles are 
present; on the opposite side of the primary bundle in the 
carene, a bundle occurs which is intermediate between the pri- 
mary and secondary bundles; this intermediate bundle is open 
interiorly only, i. e., the leptome only is in contact with the 
stereome. This is the only bundle of this type found in this 
species, but it was constant in all the asper sections examined. 
The primary bundles are enclosed by thick-walled cells, the 
mestome sheath; outside of this is a row of thinner- walled cells, 
the parenchyma sheath. In the bundles of the secondary and 
intermediate types, the mestome sheath occurs, while the 
parenchyma sheath disappears. 
Carene . — The carene consists of only one bundle, which is the 
primary type; this conforms to the description given to others 
of this kind, except that it is the largest bundle. The 
hadrome is separated from the sterome by colorless parenchyma 
cells, while a single row of thick walled sells, resembling stere- 
ome, separates the leptome from the hadrome. Two large 
pitted ducts and two spiral ducts with an intercellular space are 
present. The bundle is enclosed by mestome and parenchyma 
sheaths. Trichomes in the shape of conical projections occur 
on the inferior surface of leaf above the primary mestome 
bundle. To one side of this a secondary bundle occurs, with 
pitted and spiral ducts. On the opposite side of the primary 
bundle the intermediate bundle occurs. This is open interiorly 
only. The leptome is in contact with the stereome by means of 
two rows of colorless parenchyma cells, while the mestome 
sheatn surrounds the mesophyll. In other respects it is the 
same as the secondary bundle. 
Stereome . — Stereome occurs both on superior and inferior 
surfaces of the primary bundles. None is present in the 
bundles of the secondary type and only a very little on the 
inferior side of the intermediate bundle. Stereome occurs in 
groups of from four to six cells on the margins of the leaf. 
The walls of the stereome are frequently stratified. 
Colorless parenchyma is found beneath ail the primary bundles; 
it fills the space between the hadrome and the stereome, while 
a single row of cells enclose the whole mestome bundles. In the 
bundles of the secondary type it disappears entirely. 
