ig ee ee 
a 
1904] CHRYSLER—CENTRAL CYLINDER 173 
collateral structure. The meristeles unite at the next node and a 
single strand turns outward, leaving a wide gap in the vascular ring. 
Again the meristeles separate widely, owing no doubt to the fleshy 
nature of the stem which by this time has begun to show its habit of a . 
horizontal somewhat swollen rhizome. As the stem turns upward 
into the air the meristeles approach one another and some of them 
become amphivasal. At about this point the internal endodermis 
disappears, but the external layer becomes strongly cutinized. The 
amphivasal strands resume their collateral structure at a slightly 
higher level; medullary strands are absent in most plants. 
TRILLIUM GRANDIFLORUM.—The subterranean stem is a vertical 
rhizome which becomes thicker and more ovoidal as the plant grows 
older, owing to deposition of stores of starch. In the young stem 
the central cylinder is a solid mass of vascular tissue for a few inter- 
nodes. The first leaves have three traces; the median trace is much 
the largest, and as it leaves the central cylinder the latter becomes 
somewhat crescent-shaped; the lateral traces are very delicate and 
by their departure leave no indentations in the stele. After exit 
of the traces of the third or fourth leaf, however, there is intrusion of 
fundamental tissue into the central cylinder, since the angles of the 
crescent above referred to curve around and finally close in on the 
side next the trace. This condition is shown in jig. 20; tis the median 
trace, t, is one of the lateral traces whose gap was narrower than 
that of the median trace and had already closed at this level. The 
writer fails to see how the thin-walled tissue inside the stele can be 
regarded as anything but a portion of the fundamental tissue inclosed 
by approximation of the vascular tissue at the sides of the gap. The 
appearance above described may be masked by the overlapping of 
two foliar gaps on opposite sides of the stele; in such a case the stele 
is broken into two halves (fig. 21),.a condition which has frequently 
been described for various ferns. In the upper part of the rhizome 
the stele becomes complicated by bridges of vascular tissue reaching 
from one side of the stele to the other; also certain of the leaf traces 
tun for a short distance in the medulla before turning outward. It 
should be remarked that these medullary strands are amphivasal. 
In some Seedlings the stele retains its solid or protostelic character 
for many internodes, and it is possible that the diversity noticed in 
