Sinnott. — The Evolution of the Filicinean Leaf trace. 177 
one-half of the Dennstaedtia or Loxsoma bundle, and composed of a mass 
of metaxylem with an adaxial incurving or hook at each end, in the con- 
cavity of which occurs an endarch protoxylem group. This double trace, 
the £ Onoclea type ’ of Bertrand and Cornaille, is characteristic of the great 
mass of smaller and simpler Mixtae as well as of Onoclea (Text-fig. 8). In all 
ferns examined where this trace was present the important fact was noticed 
that the adaxial (lateral) protoxylem group of each bundle, whenever it was 
distinguishable reasonably early on the course of the trace through the 
cortex, was always mesarch and near the outside of the bundle (Text-fig. 7 
Fig. 6. The base of the leaf-trace of Plagiogyria. 
Fig. 7. The base of a leaf-trace of the Onoclea type. 
Fig. 8. The petiolar bundle of the Onoclea type. 
Fig. 9. The base of the leaf-trace of Cyathea Macarthuri , showing the method of formation of 
a many-bundled arch. 
and PI. XI, Fig. 17), becoming endarch only by the gradual disappearance of 
the metaxylem between it and the adaxial parenchyma. Several instances 
were observed where the other protoxylem (median or abaxial) was also 
mesarch, but never in such a striking way. This condition of mesarchy 
was apparent even in such delicate ferns as the three species of Phegopteris 
which were examined. It is important in connexion with our hypothetically 
primitive leaf-trace, for two such Onoclean bundles as shown in Fig. 17, if 
closely approximated by their adaxial faces, would produce a triangular 
mesarch bundle very similar to that which we have considered ancestral for 
the group. 
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