The Schizeeaccae . 
*53 
the spiral elements of the two lateral protoxylems disappear, and 
finally the prominence on the lower side becomes narrower, the 
two spiral protoxylem-strands being replaced by a single strand of 
narrow scalariform elements which are probably continuous with 
the peripheral protoxylem of the stele. The phloem, which in the 
petiole is continuous round the whole strand, with large metaphloem 
elements localised between the angles, is evenly distributed round the 
xylem at the base of the leaf-trace. It is not quite easy to explain 
Fig. 48. 
Fig. 47. 
Fig. 47. Lygodium japonicum. T. S. of petiolar strand. After Prantl. 
Fig. 48. Schizcea clcgans. T. S. of petiolar strand. After Prantl. 
this peculiar type of petiolar strand, but I am certainly inclined to 
regard the rounded form of the xylem and the continuous phloem, 
both characters especially marked at the base of the leaf-trace, as a 
primitive character, just as I regard the somewhat similar structure 
of the base of the leaf-trace in Tricliomaues radicans in the same 
light. It may here be noted that the leaves of some species of 
Lygodium, though constructed on the same general plan as those 
of Gleichenia, show more tendency to true dichotomy in their 
branching and in the lobing and venation of their laminae. 
The genus Schizcea consists of small ferns, mostly characteristic 
of shady forests, and largely tropical. The fronds of many species 
are truly dichotomous. The stele of the rhizome is of peculiar 
type. The thin ring of xylem surrounded by phloem, pericycle and 
endodermis, encloses a parenchymatous pith which does not, as in 
most ferns, resemble the cortex histologically, but is usually thin- 
walled, like xylem-parenchyma ; in 5. digitata it is sclerotic, though 
even here it differs from the sclerotic cortex. In some species also it 
contains, locally, tracheids mixed with the parenchyma, occasionally 
so many that the stele is, at certain levels, little removed from a 
protostele of the Lygodium- type. There seems in fact little doubt 
that the stele of Schizcea is derived from such a protostele, most 
of the central tracheids being replaced by parenchyma in relation 
