510 Tansley and Chick. — On Schizaea malaccana. 
Fig. 8. Longitudinal section passing through side of leaf showing a stomatal 
row with the alternation of stomata and inter-stomatal cells, and the armed 
longitudinally elongated mesophyll cells, x 60. 
Fig. 9. Transverse section of stele of root with inner layer of cortical cells. 
Px. proto xylem, phloem, per. pericycle, end. endodermis. x 200. 
Fig. 10. Median longitudinal section of apex of small stem showing apical cell 
and common origin of endodermis, pericycle, xylem and phloem from middle 
segment ( m .) of the anticlinal series of three formed by division of primary segments 
of apical : 0. outer, m. middle, i'. i r . anticlinally divided inner segment, formed by 
periclinal division of primary segment of apical cell; me. external segment of m. 
( = common mother-cell of endodermis and pericycle), mi. internal segment of m. 
( = common mother-cell of xylem and phloem), e. endodermis,/. pericycle, ph. 
phloem, x. xylem, h. mucilage-forming hair, x 200. 
Fig. 11. Transverse section of stele of large stem in meristematic region, close 
behind the apex, showing clear differentiation of the three layers, derived from 
the three series of cells shown in Fig. 10. The central cells, forming the young 
pith, p. , have mostly completed their divisions. The nuclei of those to the left 
(unshaded) have already entered the resting condition in which they take up 
haematoxylin much less readily. The middle zone, which is the initial zone 
of the vascular ring and its sheath, is thin- walled, and its inner division, v. r., 
still often only two cells thick, corresponds to the mother-layers of xylem and 
phloem. At l. and r. the middle zone is thicker owing to the formation of a 
leaf-trace and of a root respectively. The outer division of the middle zone 
is the sheath-layer, or coleogen, col., the mother-layer of endodermis and pericycle. 
This is still undivided except about the line l. Its cells are thin-walled and have 
darkly staining nuclei. Their common origin with the mother-layer of the 
vascular ring is extremely obvious. The outer zone, of which only the inner 
layers are shown, of larger thick-walled cells with resting (unshaded) nuclei, forms 
the young cortex, cor. Its divisions are practically complete, x 2 50. 
Fig. 12. Transverse section of young stele of same stem further back than 
in Fig. 11, showing coleogen divided into endodermis, end., and pericycle, per., 
and origin of sieve-tubes. The cells of the young phloem, ph., whose walls 
are darkly shaded, already show the peculiar light blue colour with fuchsin- 
iodine-green characteristic of the walls of sieve-tubes in this plant. Some 
of them still possess nuclei. At A the differentiation of the stele is not so far 
advanced, and the accurate radial seriation of the mother-cells of endodermis, 
pericyle, xylem and phloem is well seen. This seriation can also be traced in 
other parts of the section where the mother-cells of xylem and phloem have 
already divided. 
e.r., e.r., two endodermal cells belonging to two endodermal rods (proving the 
early differentiation of the internal endodermal structures) one of which dies out 
almost at once, while the other is continuous with an internal endodermis also 
dying out below, x 240. 
Fig. 13. Transverse section of stele of same stem further back than in Fig. 12, 
showing completed differentiation of pericycle and endodermis and of phloem-ring, 
broken by departure of a leaf-trace ; also progressing differentiation of xylem-ring, 
x., exhibiting its endarchy. end. p., endodermal pouch, enclosing here one file of 
cells. 1 . t., leaf-trace with xylem not yet differentiated, x 175. 
