EQTJISETINEM. 
399 
forms a leaf-sheath, and the corresponding internode or joint of the stem. The 
above-mentioned divisions take place in the three segments during their arrange- 
ment into a transverse disc, each segment becoming converted into a mass of cells 
consisting of from four to six layers. As soon as the transverse zone is formed, 
the formation of the leaves commences by the growth of the outer cells of the 
segments. They form an annular ridge; one of the upper transverse cell-layers of 
the whorl of segments projects out- 
wardly, forms the apex (the circular 
apical line) of the ridge (Figs, 279, 280, 
bs), and those of its cells which lie 
most externally (the apical cells) divide 
by walls inclined alternately towards 
and from the axis. The circular apical 
line becomes more and more elevated, 
and thus the annular ridge becomes a 
sheath enveloping the end of the stem. 
This same layer, of which the outer- 
most cells form the apical line of the 
annular ridge, produces in the interior 
of the sheath a meristem in which the 
fibro-vascular bundles of the leaf-sheaths 
arise. The lower transverse cell-layers 
of the whorl of segments grow only 
slightly outwards and upwards, become 
divided by vertical and afterwards rapidly 
by transverse walls, to produce the 
tissue of the internode, which passes 
gradually into that of the leaf. A ver- 
tical layer of this tissue forming a hollow 
cylinder (Fig. 280, v v) is distinguished 
by numerous vertical divisions; it forms 
a ring of meristem (procambium, thick- 
ening-ring in Sanio's sense), in which 
the vertically descending fibro-vascular Fig. 280. — Left half of a radial longitudinal section beneath the 
„ - , , J ~ apex of an underground bud of /:"yz<2ji'i'«w ^£'/w^^^^'^^V^; in September ; 
bundles 01 the mternOde are lOrmed. /^-lower part of the vegetative cone, <J'<^" 5"' leaves, *j their aplcal 
1 ji r 1 • cells, r' r" r'" the cortical tissue of the corresponding internodes ; 
1 heSe bundles lOrm the prolongations ^ pith, w v thickening ring, s S layer of cells from which the 
1 . I 1 fibro-vascular bundles of the leaf-tooth arises. 
01 those ot the leaf-teeth, which they 
meet, as shown in Fig. 281,^/, at an obtuse angle, and coalesce to form curved 
* common' bundles. The layers of cells which lie outside the ring of meristem 
that gives rise to the bundles produce the cortex of the internode, in which air- 
conducting canals soon arise. Even at an early period the first rudiments of the 
sheath-teeth appear as protuberances at regularly distributed points, each of them 
ending in one or two apical cells (Fig. 282) \ 
* On the original number and subsequent increase of the sheath-teeth, &c„ compare Hofmeister 
and Reess, /. c. 
