Feb. 1,1925 
Vegetative Organs of Sugar Cane 
213 
The cells of the outer epidermis of 
the sheath resemble those of the stem 
(pi. 13, C). They are very thick- 
walled, undulated and pitted. The 
short cells are very conspicuous and in 
specialized regions, as for example at 
the blade joint, they are more numer¬ 
ous than elsewhere. The cells above 
the veins are always long and narrow 
and possess a nearly closed lumen; 
those between the veins are broader, 
but otherwise structurally the same. 
The epidermal cells of the sheath 
joint and the flanges of the blade joint 
are thin-walled and irregular in shape. 
Stomates and hairs are well developed. 
The former occur in longitudinal rows 
next to the veins. The hairy covering 
is most extensive above the sheath 
joint (pi. 14, B) and at the flanges of the 
blade joint. Above the sheath joint 
the number of hairs decreases greatly, 
coincident with a change in their 
character. Instead of the extremely 
long and delicate hairs which are 
characteristic of the regions referred to 
above, short and strongly lignified setae 
interspersed witl + wo-celled appressed 
hairs are found. 
THE LIGTJLE 
The ligule contains no vascular tis¬ 
sue but is made up altogether of elon¬ 
gated parenchyma cells which are com¬ 
paratively thin-walled and of cellulose. 
Both inner and outer epidermis are 
suberized. The outer epidermis, the 
one next to the sheath, is covered with 
numerous long hairs which, arising at 
the base of the ligule, are adnate to 
the epidermis (pi. 13, C) and become 
free at the apex where they form a 
minute fringe. The hairs are com¬ 
monly strongly lignified at the base. 
The outer epidermal cells are fairly 
thick-walled and slightly undulated; 
the inner ones are broad, especially at 
the base, the walls are thin and more 
undulate than those of the outer epi¬ 
dermis. All epidermal cells are of one 
type, silicified cells as well as stomates 
being absent. The ligule has a pro¬ 
tective function in that it prevents the 
entrance of water between stem and 
sheath. 
THE LEAF BLADE 
The tissues of the blade are con¬ 
tinuous with those of the sheath and 
in general show similar structure. Dif¬ 
ferences such as are found are consistent 
with the chief role of the blade as an 
organ for assimilation and aeration. 
The vascular bundles are of three 
ranks (pi. 16, C): (a) small round 
bundles, (6) medium large oval bun¬ 
dles, and (c) large rhomboid bundles. 
The small and medium large bundles 
alternate with one another, whereas 
the large bundles, corresponding with 
the more prominent veins of the leaf, 
appear at wider intervals. The large 
bundles are always bound on either 
side by a small round bundle. The 
small bundles are always close to 
the lower epidermis, whereas the other 
two types occupy the middle of the 
blade. In the region of the midrib 
(pi. 16, B) however, a layer of colorless 
parenchyma is interpolated between 
the bundles and the upper epidermis. 
This layer increases in thickness, press¬ 
ing the vascular tissue gradually 
toward the lower surface, while the 
scattered sclerenchyma groups on the 
upper surface unite to form a solid 
band. The resulting tissue area has 
the form of a half moon, or triangle, 
the lower surface of which is studded 
with vascular bundles, while the upper 
surface, which contains no bundles, is 
reinforced by a solid layer of scleren¬ 
chyma. 
The bundles of the blade differ pri¬ 
marily from those of the stem in that 
they possess a chlorophyll-bearing bun¬ 
dle sheath and an inner sheath in the 
region of the phloem (pi. 1, D). The 
vascular tissue itself differs in the lack 
of a protoxylem lacuna except in the 
very large veins, and in a greater devel¬ 
opment of the xylem (pi. 17, A). 
The chlorophyll-bearing bundle 
sheath, which forms a continuation of 
the sclerenchyma sheath of the stem 
and leaf sheath bundles (pi. 17, B), 
is made up of uniform large and 
spherical cells which vertically have 
the form of short cylinders (pi. 18, 
B, C). In the region of the phloem 
pole of the large bundles the sheath 
cells become smaller or may even be 
wanting. Through the gap, which is 
formed thereby, the fibers of the inner 
sheath become continuous with the 
fibers of the hypodermal sclerenchyma. 
But while the fibers of the inner sheath 
appear, in some instances at least, 
ontogenetically the same as those of the 
hypodermal sclerenchyma, they differ 
structurally in that the former possess 
numerous pits. In small bundles, 
where the cells of the inner sheath are 
undifferentiated as yet, the phloem is 
separated from the chlorophyll-bearing 
sheath by a layer of parenchyma cells, 
which differ from the phloem cells 
only by their larger size. 
The xylem of the large bundles 
consists of two large vessels connected 
by a more or less extensive band of 
small pitted elements, most of which 
are narrow vessels. In the small 
bundles there are only a few rela- 
