Feb. 1, 1925 
Vegetative Organs of Sugar Cane 
217 
cells which separate the groups of pro- 
toxylem are elongated, rectangular, 
and profusely pitted; those at the 
periphery of the pith are sclerenchvma- 
tous pointed, and sparingly covered with 
narrow slanting pits. The thickening 
and lignification 6f these scleren- 
chymatous cells begin soon after the 
protoxylem is formed and while the 
large vessels are still meristematic. 
The first of these cells to become ligni- 
fied are those adjacent to the pit 
and the process of maturing is thence 
continued in centrifugal direction (pi. 
20, B, and pi. 23, A). The order of 
development differs therein from that 
of the protoxylem, which is in the 
direction of the root axis. 
The structure of the protoxylem of 
the root is peculiar in that it lacks 
annular and spiral elements. The 
first-formed cell is a narrow element 
with scalar if or m or spiral-reticulate 
wall thickening; the second protoxy¬ 
lem cell is similar though often much 
larger than the first one and is usually 
scalariform. Quite frequently the 
larger of the two protoxylem cells 
develops first and only later a small 
cells is added centrifugally. 
The groups of phloem alternate 
with the protoxylem. They are al¬ 
ways small and rarely contain more 
than eight elements. The cells of the 
phloem are pentagonal or square in 
cross section and are readily recognized 
by the slightly thickened refractive 
walls (pi. 23, B). 
In old roots all the cells of the vascu¬ 
lar tissue, with the exception of the 
phloem, become lignified and thick- 
walled. Similar changes take place 
in the layer of cortical cells which 
border on the endodermis. Concom¬ 
itant with these changes is a disinte¬ 
gration of the cortical tissue. The 
radial strips of tissue which remain 
are attached to the exodermis on the 
one hand and the sclerotic layer of 
inner cortical cells on the other (pi. 
21, B). Occasionally certain cells 
of the inner cortex do not lignify so 
that the radial strips of cortex become 
attached to the endodermis directly. 
ONTOGENY 
Material for study was selected from 
the apical region of a large, actively 
growing cane. The stem portion 
measured 9 cm. and contained 14 
internodes of which the upper 10 were 
crowded into a space of only 10 mm. 
(fig. 7). The relative length of the 
leaf sheath and blade of the first 14 
leaves follows on page 218. 
