The Hymenophyllacece. 115 
partly becomes attached to the two incurved free edges of the xylem 
arch and partly is scattered in the central parenchyma (Fig. 28 B). 
A B C 
Fig. 28. Trichotnanes radicans. 
Diagrams, (from Boodle). 
A. Strand of petiole, x 95. 
B. Strand of petiole just above point of departure of axillary 
branch, x 95. 
C. Relations of strands of petiole and axillary branch to stele 
of rhizome shown in longitudinal section. X about 6. 
These three centres of differentiation are in relation to the supply of 
the two rows of pinnae and the rachis respectively. The whole 
structure I should regard as a modification of the type of petiolar 
strand found in T. reniforme by the differentiation in the rachis of 
the frond of more or less separate water channels, which are not, 
however, continued down so far as the base of the petiole. The 
stem-like structure of the strand below the junction of the leaf 
and branch-traces might of course be explained by the hypothesis 
that this basal portion is really a stem-structure on which the leaf 
is inserted, but this consideration, even if valid, will not apply to 
the structure of the petiolar strand above its junction with the 
branch strand. The whole of the phenomena, taken in conjunction 
with those seen in T. reniforme, appear to lend decided support to 
the interpretation of leaf-strand and stem-stele as primitively 
identical structures. 
T. Prieurii has an upright stem with a two-fifths phyllotaxy. 
The structure of the stem-stele, leaf-trace and petiolar bundle does 
not differ very much from that of T. radicans except that the 
central parenchyma of the petiolar stele is replaced by sclerenchyma, 
which, with the protoxylem, is decurrent into the stele of the stem, 
but eventually dies out. There may be two, three, or four proto- 
xylems in the petiole. The decurrency of sclerenchyma in the 
