IOWA ACADEMY OF SCIENCES. 
139 
These different types do not always occupy the same relative 
position in the leaves of the different species. 
In the species studied, these bundles are found to occur in 
three distinct sizes with constant positions. This would have 
afforded a basis of nomenclature for the bundles but for the 
fact that it does not hold good for other genera, and hence is 
not used. However, for convenience in locating the structural 
types described above, their position in the leaf is indicated by 
the parenthesis “(carene)” which is the largest vein in the leaf 
and always central; “(vein 2)” the next smaller veins, occur- 
ring at nearly regular intervals between the carene and the 
edge of the leaf (PI. xvi, Pig. 2); and “(vein 3)” the smallest 
veins, which occur in groups of three to six between the medium 
veins (vein 2) and also between them and the carene. 
ERAGROSTIS REPTANS NEES. 
(PI. xvi, Fig. 1; PI. xviii, Figs. 17 and 18.) 
Epidermis — This, the smallest of the species studied, pre- 
sents the most striking variations from the general type, espe- 
cially in the epidermal characters. The walls of the epidermal 
cells on the superior surface are quite thin, while those of the 
inferior surface are thicker. The inferior epidermal cells are 
nearly equal in size, as are those of the superior surface, but 
these latter are much larger in proportion than those of any 
other species. Stomata occur frequently on both surfaces, on 
either sideof the mestome bundles. Trichomes are long, slender, 
pointed, one -celled hairs, occurring in single rows on all bundles. 
The two adjacent epidermal cells, in some cases, extend 
obliquely upwards beside the base of the trichome. 
Bulliform cells . — The bulliform ceils are two or three in num- 
ber, and in some cases not easily distinguishable from the epi- 
dermal cells. 
Mestome l)undles . — The mestome bundles are thirteen in num- 
ber, and are all of the intermediate type. The chlorophyll- 
bearing parenchyma sheath is composed of four or five large 
^ cells and is open below. Leptome, hadrome and thick- walled 
parenchyma are well developed in all the bundles. In the 
bundles of the carene and vein 2 the mestome sheath is inter- 
rupted above by the stereome, but in the other bundles (vein 3) 
it is continuous. 
The carene bundle differs from the other bundles only in 
being slightly larger, and in having the leptome entirely sur- 
rounded by thick- walled parenchyma. 
