ec od 
1898-99.] |. MORPHOLOGY OF THE CENTRAL CYLINDER IN THE ANGIOSPERMS, 621 
becomes tubular, as in the young stems of the ranunculaceous species 
described above. The tube has, likewise, both an internal and external 
phlceoterma, and the stelar tube is characterized by the same foliar gaps, 
around the margins of which the internal and external phlceotermas 
communicate. When the young stem has reached a length of from four 
to eight centimetres, the foliar gaps begin to overlap, and the two 
concentric strands which are at present in the mature stem make their 
appearance. When the stem passes out of the mud into the water 
to form the well-known floating shoots, the xylem degenerates and is 
represented merely by a cavity in each of the two stelar strands. 
Photograph 22, plate 10, represents a section through the young tubular 
stelar system of Svrasentza purpurea, at a point where a leaf-trace is 
being given off, and is subtended by its corresponding foliar gap. It 
will be obvious from the above description and the accompanying 
photograph that the young stelar system of Srasenia purpurea is 
primitively tubular. 
Two species of Nuphar have also been examined in this connection. 
Nuphar luteum, var. Kalmtanum, is very favorable for study on 
account of the relative simplicity of its stelar system. The young 
epicotyledonary central cylinder is here also, at first, a pithless strand, 
and only after the exit of several leaf-traces does it become tubular with 
a pith of fundamental tissue. The stelar tube is provided with an 
internal as well as an external phlceoterma. Photograph 22, plate Io, 
represents a section through the young rhizome at a point where a leaf- 
trace has just been given off and a second one is in the act of making 
its exit from the tubular central cylinder. In the older rhizome, the 
foliar gaps begin to overlap, so that in a transverse section the stelar 
tube seems to be broken up into two or more segments, each surrounded 
by its own phlceotermal sheath. The number of fibro-vascular segments 
become subsequently increased by the fact that several leaf-traces are 
given off to each leaf. Finally the stelar tube becomes entirely 
unrecognizable by reason of the increasing complexity in the arrange- 
ment of the vascular strands. 
The stelar development of Vuphar advena is very similar to that of 
the species just described. In this case, the epicotyledonary fibro- 
vascular strand passes quite rapidly into the tubular condition. The 
fibro-vascular cylinder has likewise internal and external phlceotermas 
which communicate through the foliar gaps. Very soon the leaf-traces 
to the individual leaves become numerous, and the stelar tube is 
consequently interrupted by a large number of foliar gaps. The com- 
plexity is subsequently further increased by the appearance of an 
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