SPOROPHYTE. 19 
Only rarely do two elements lie adjacent radially. The walls are thick, 
but not lignified, and are beset with deep pits with rounded, flaring aper- 
tures. They are best seen in the very young regions (figs. 107, 110) 
where lignification is just beginning to occur in the xylem (see table below). 
The phloem forms a continuous ring, one to three cells in thickness. 
The cells are angular and appear in cross-section to be empty; their ends 
(fig. 65) acute, but not finely tapering. These are sieve-tubes, but the 
sieve-plates are only found with some difficulty. I could not demonstrate 
callus, either with azoblue or coralline soda. 
TABLE 5.—Measurements in millimeters of cells of various tissues in the stem. 
Length. Radial diameter. Tangential diameter. 
Tissue — 
Aver. | Max.| Min. | Aver. | Max.| Min. Aver, | Max.| Min. 
Epidermis.............. O.1 0.16 | 0.064)/0.02 0.03 |0.014 |0.035 |0.0372/0.032 
Outer sclerotic cor- 
TOK ccc chetsuewuasacsans R2OG- | ics c sees ctmasines -037 L047 O32? | Meannacastss| Veawcecallenees oo04 9 
Inner sclerotic cor- 
LO Xinaictiw viens dswe sionwie - 336 -44 -21 | .O51 F066" |) 6O32) “lassnsoevennlersinoiealaaisnonenss 
Starchy cortex........ 142 .246) .088] .042 05 5032. |insissabwnclsendeciine [ud naonveies 
Outer endodermis...) .063 .078! .057| .00825] .009 | .00714 0214] .O14 
Outer pericycle.......| .o1g47) .16 | .127| .o157 | .o178} .or4 032 | .o178 
Outer protophloem..) .678  J.......0.Jecseeeees GOOSO2| sheer lanenerhc oz: Mablaa needs Meagemnct eames ois 
Outer phloem..........)-s:eeeeee get | Teh | <O164 | 2025 | sO13 — leevensensed|severione|svaeesaens: 
Outer conjunctive 
parenchyma........ SLOP || sarewrw se lonsseniins LOUDF | decoder eens sceerone | Seauee rents lnatismase leweaaeetesee 
Kylem.....csecceereeeeee[eereeeeeees 4.4 | 1.6 | .06 -078 | .032 057 | .02 
Inner phloem.......... i cieiisig'd vise all w han aineleisl \oawaas eee -O155 O21 OLZ4 fercereeeeee|eceererenleseeeereces 
Inner endodermis...| -°99 -149| .082] .0083 | .or4 | .0071 022 | .0178 
Starchy medulla... - 166 -204) .105) .034 SO3Q || 6OZ5- [carnvvjearies| sicasanione fiereos seney 
Between phloem and xylem lie the thin-walled, angular, starch-laden cells 
of conjunctive parenchyma (figs. 63, 64, 81). They are about twelve 
times as long as wide, and have tranverse or oblique end-walls. Some of 
these cells may extend in between the xylem tracheids, and rarely such an 
extension joins with the inner conjunctive parenchyma, completely inter- 
rupting the xylem. Sometimes the conjunctive parenchyma is interrupted 
and a sieve-tube lies directly against a scalariform tracheid. 
With the above exception the xylem is a continuous ring of larger and 
smaller scalariform tracheids, with thick, lignified walls (figs. 63, 67, 97). 
The middle lamella is clearly discernible. In places this ring includes but 
one radially widened xylem element; in other places it may be three cells 
thick. There are no spiral elements in the stem. The tracheids are of 
the usual long, pointed type (figs. 78, 79; see table above). 
The inner tissues so closely resemble the outer that they may be described 
simply by comparison (figs. 63, 64). Conjunctive parenchymas show no 
difference. The inner phloem is mostly one, often two, cells thick, and the 
sieve-tubes are narrower than the outer ones (see table above). Proto- 
