260 BOTANICAL GAZETTE [APRIL 
is in the position of the protoxylem. In the petiole of every living 
genus of ferns except Lygodium, the first-formed tracheids are 
endarch, and the upward development of the filicinean leaf seems 
to be uniformly marked by the disappearance of its centripetal 
wood. At the base of the leaf trace in many ferns a mesarch 
condition still persists. Here the protoxylem is usually simply 
mixed indiscriminately in the metaxylem, but in those rather rare 
cases where it shows a definite attachment either way, it almost 
always becomes continuous with the centrifugal wood. The base 
of the leaf trace of Thamnopteris, a primitive osmundaceous fern, 
as described by Kipston and GwyNNE-VAUGHAN (3), is a good 
example of this. Endarchy and the attachment of the protoxylem 
to the centrifugal wood are therefore distinctive characters of the 
advanced filicinean foliar bundle. 
The close affinity of the Cycadofilices to the ferns is manifest 
in the structure of the leaf trace as well as in many other char- 
acters, and there seems good reason to believe that the foliar 
strand in this group of early seed plants has been derived from a 
bundle very similar to that of Clepsydropsis or Asterochlaena. 
The most primitive genera of the Cycadofilices and those which 
approach the ferns most closely in all their characters are Cala- 
mopitys, Lyginodendron, and Heterangium. In Calamopilys, which 
is a very ancient form, going back to the Devonian, the base of the 
leaf trace, while still one of the bundles which surrounds the pith, 
is a single strand, with a cluster of protoxylem mixed with pater” 
chyma at its center. In most species the centripetal wood becomes 
reduced at the very base of the bundle, and in C. Beinertiana, %® 
described by Scorr (5), it is actually broken through, the Pr 
toxylem becomes continuous with the centrifugal wood, and an 
endarch condition results. As the single mesarch trace leaves 
the stele, its protoxylem group divides into two parts, which lie 
near the outer face of the bundle, and each of these soon divides 
again into two. The trace on becoming free splits equally in 
two diarch, mesarch, and concentric strands, which pass out through 
the cortex. In the base of the petiole these split up into an arc of six 
bundles. The primitive monarch condition is therefore present e 
the very base of the trace; this soon takes on the diarch structure 
