404 BOTANICAL GAZETTE [NOVEMBER 
they belong to the strata that cover the mesophyll or the stereome. ! 
Those covering the mesophyll are either developed as bulliform cells 
(S CG in fig. 2) with nearly straight walls, or as ordinary epidermis | 
cells with numerous stomata (.S, in fig. 2). The cells of the stomatif- : 
erous strata have distinctly undulate cell walls, and these strata form 
longitudinal bands on both sides of the bulliform cells. Very differ- 
ent from these strata are those which cover the stereome (A, in fig. 2). 
Here we find cells of very different size, short and almost fusiform, or 
rather long, but all showing numerous foldings of the cell walls. Two 
forms of epidermal expansions are to be found here, viz., some which 
are short, one-celled and thorn shaped, and small hairs consisting of 
two cells (#7, in fig. 2). This structure is to be found on the entire 
surface of the leaf in regular alternation and with almost the same 
number of rows in each stratum (fg. 2). There is in this way nothing 
to indicate the median part of the blade, for it shows no larger devel- 
opment of the bulliform cells, and, as will be shown later, the median 
mestome bundle and its surroundings do not show any histological 
difference from those of the lateral parts of the blade. 
If we consider the epidermis of the inferior face of the leaf we find 
only a few differences from that of the superior one. The hairs seem 
here to be most frequent in the stomatiferous strata ; the cells which ae: 
round the stomata are exceedingly thick walled, and no proper bulli- 
form cells are developed, so that the stomatiferous strata occupy the 
entire space between those which cover the stereome. As shown 1 
Jig. 3, the epidermis of the inferior face shows a certain development 
approaching that of bulliform cells, but widely different from 4 
Purshii, which exhibits true bulliform cells on the inferior face of the 
ade. ‘ 
The mestome bundles are of a very uniform development, and, as 
Stated above, the median bundle is not more prominent than the 
others. Only two forms may be distinguished, but the difference 
relatively smaller than we have seen in the other genera described . 
our previous articles upon this subject. Both forms of mestome bun se 
dles are surrounded by a completely closed and colorless parenchy i 
sheath (P, in fig. 5), inside of which is a mestome sheath of a i 
walled cells. The larger bundles show the presence of a single Be : 
of thick walled mestome parenchyma, separating the leptome from me oe 
hadrome; and in the smaller bundles this parenchyma is absent. 
smaller bundles appear to be the more numerous. 
