.Feb 1, 1925 
Vegetative Organs of Sugar Cane 
211 
celled parenchyma instead. A cross 
section through the sheath joint just 
above the insertion on the stem (pi. 
15 ; D), shows an increase in the num¬ 
ber of bundles over that of the sheath 
proper, and their partial radial dis¬ 
placement. As a result of these 
changes, no longer are there rows of 
superimposed bundles, but more or 
less definite .tangential bands, with 
each band containing bundles of a 
different magnitude. The bundles of 
the inner band, that is, the ones clos¬ 
est to the inner epidermis, are the 
largest and most widely spaced, and 
are often compound. They constitute 
the large leaf-traces which, as may be 
seen from a study of the course of the 
vascular bundles, penetrate far into 
the stem and extend to a depth of 
several internodes. Often, just before 
passing out into the leaf, two or even 
more bundles fuse more or less com¬ 
pletely, which accounts for the presence 
of the compound bundles in the sheath 
joint. The second circle contains 
smaller bundles which penetrate less 
deeply and are much shorter in vertical 
extent. Finally, the outer circle is 
formed by small groups consisting 
mostly of collenchyma (pi. 13, E). 
The structure of the large bundles 
resembles somewhat that of the bundles 
found in the intercalary zone of the 
stem. On the xylem pole of the 
bundle there is a large collenchyma 
cap which is separated from the bundle 
itself by a single layer of parenchyma. 
The xylem is composed of spiral ele¬ 
ments which partly surround the 
phloem. The smaller bundles have 
increasingly larger amounts of collen¬ 
chyma, and the smallest may be 
exclusively collenchyma. Both below 
and above the sheath joint the collen¬ 
chyma terminates and is replaced by 
sclerenchyma. The supernumerary 
bundles gradually disappear, and be¬ 
tween the radial rows of bundles the 
parenchyma exhibits partial disinte¬ 
gration with the formation of the 
typical air cavities. 
In the growing cane, the lower, 
older leaves are progressively shed, 
constituting the so-called process of 
“self cleaning” typical of this group of 
cane varieties. In the mature plant 
there is a naked stalk with a tuft of 
large leaves at the apex. The leaves 
become detached from the stem in the 
region of the sheath joint, which, as 
previously discussed, is anatomically 
different from the other regions of the 
leaf, in that the sclerenchyma fibers 
are replaced by the much softer 
collenchyma. The sheath joint may 
in this connection be considered the 
abscission zone of the leaf. 
The apex of the sheath also under¬ 
goes modifications before it merges 
into the blade. As the leaf sheath 
approaches the blade joint it becomes 
narrower and thicker, thereby crowd¬ 
ing the vascular bundles more and 
more together. The air cavities be¬ 
tween the bundles disappear, being 
replaced by parenchymatous tissue. 
The sclerenchyma groups near the 
outer epidermis , gradually enlarge, 
while the vascular bundles at the same 
time move closer to the center of the 
sheath. The sclerenchyma groups of 
the inner epidermis also enlarge con¬ 
siderably and gradually unite into a 
solid tangential band (pi. 15, C). 
While these changes are going on, 
the tangential band of sclerenchyma 
becomes separated from the inner 
epidermis by a progressively widening 
band of parenchyma (pi. 15, C). 
The part of the sheath just above 
the insertion of the ligule has been 
referred to as the blade joint (pi. 1, C 
and fig. 5). The flanges of this joint 
are brownish in color, strongly pubes¬ 
cent, and of a soft texture. The vascu¬ 
lar tissue in this region resembles that 
found in the sheath joint. As in the 
latter the large bundles inclose much 
collenchyma, whereas the xylem con¬ 
sists entirely of spiral vessels. The 
vascular tissue of the median blade 
joint, which becomes continuous with 
the bundles of the midrib of the blade, 
does not show the modifications ex¬ 
hibited by the flanges. If there are 
any noticeable changes they are in the 
direction of increased lignification and 
the formation of ever broadening 
lignified bundle caps. In the transi¬ 
tion region from the median part of the 
blade joint to the flanges, there is 
noticeable a gradual transformation 
of the sclerenchyma into collenchyma; 
one frequently observes bundles which 
have thick collenchyma caps, of which 
half of the cells consist of lignified 
sclerenchyma. 
The inner epidermis of the sheath 
differs fundamentally from the outer 
epidermis in that the cells of the 
former are large, uniformly rectangular, 
and of one type, since the short 
silicified cells are wanting (pi. 5, B). 
Hairs and stomates are only sparingly 
developed, except just above the in¬ 
sertion point of the ligule, where they 
form a dense fringe. This same type 
of epidermal cell is found on the inner 
surface of the ligule (the side which 
is opposite the stem). The cells 
just below the ligule are broad and 
more or less irregular, whereas above 
the ligule they show a transition to 
the cells of the leaf blade, and become 
long, narrow, and thick walled. 
