124 
IOWA ACADEMY OP SCIENCES, 
Bulliform cells . — These occur only on superior surface of leaf 
and vary in number from three to seven. These cells are large 
and well marked, especially the central cells of the group; the 
outer are smaller and blend with the epidermal cells. The cuti- 
cle is not so strongly developed over the bulliform cells as else- 
where. 
Mestome bundles . — These number from thirty -three to thirty- 
five and are of three types. First, primary, in which superior 
and inferior surfaces of leaf are open, i. e., the leptome is in 
direct contact with the stereome and the hadrome separated 
from it only by the uncolored parenchyma cells. From thir- 
teen to fifteen of these bundles are present, varying in size 
from the carene to the tip of leaf. In the secondary type, lep- 
tome and hadrome are entirely surrounded by chlorophyll 
parenchyma. The bundles in this type number from fifteen to 
seventeen; they alternate regularly with those of the primary 
type except between the sixth or seventh primary bundles 
counting from the mid-rib where two of the secondary type 
occur in succession. Only two bundles of the intermediate type 
occur. These are found near the margins of the leaf. They 
have leptome in contact with stereome only. Surrounding all 
the bundles occur both parenchyma and mestome sheaths. 
Carene . — Only one bundle present in the carene. It is of the 
first type and is remarkable for the large amount of stereome 
on the superior surface of leaf. The leptome and hadrome are 
separated from each other by two rows of thick- walled paren- 
chyma cells. The leptome is separated from stereome only by 
the parenchyma and mestome sheaths, while the hadrome is 
separated from the stereome by a large number of colorless 
parenchyma cells. On either side of the carene, the small sec- 
ondary bundles occur. In these the leptome and hadrome seem 
to be in direct contact with each other. Both sheaths are 
present. 
Stereome . — No stereome occurs around the secondary bundles. 
It is abundant on superior and inferior surfaces of the primary 
type and on superior surface of the intermediate bundles. A 
group of Ihese cells also on margins of leaf. Stereome cells 
are marked with small canals. 
Colorless parenchyma . — This occurs beneath all primary 
bundles, while a sheath encloses all the bundles. 
Mesophyll . — This surrounds all the secondary bundles and 
occurs between the other two types, and on inferior portion of 
the intermediate type. 
