D aval lias and the Petiole of Lygodium . 
499 
[A photograph of the petiolar trace of L . scandens giving off the trace 
to a primary branch is shown in Plate XIV, Photo 9.] 
Lygodium JAPONICUM. All branches of the leaf except the lowest 
terminate in a suppressed growing point, and bear a pair of secondary 
branches just below the apex (Text-fig. 2, A). The petiolar trace (Text- 
fig. 2, C ; Plate XIV, Photo 10) agrees in general plan of construction 
with that of Lygodium scanderis . The lateral protoxylems appear to be 
quite exarch ; they very early become crushed by the surrounding paren- 
chyma. The median protoxylem is single, and in several cases was obviously 
mesarch with a closed ring of centrifugal metaxylem on its abaxial side 
(Text-fig. 3, A ; Plate XlV, Photo 10)* In other cases the persistent 
centrifugal elements are confined to a small group immediately abaxial 
to the actual protoxylem and separated by parenchyma from the xylem 
D 
Text-fig. 3. Lygddiiuit jdpomaim. Diagrams showing position of abaxial protoxylem. 
teeth on one or both sides (Text-fig* 3, B, c, D, e). The actual proto- 
xylem elements are very soon crushed by the surrounding cells of the 
xylem parenchyma, which become somewhat enlarged. Often all the 
centrifugal tracheae become crushed at the same time as, or shortly 
after, the actual protoxylem ; in this case the extremity of the median 
lobe is occupied by a little bay of parenchyma, which includes the crushed 
protoxylem and centrifugal elements and separates the two teeth composed 
of scalariform elements. In fact the lobe appears to be bifid and to possess 
two protoxylems. 1 The actual protoxylem is, however, always single, and 
is usually more or less attached to one of the teeth of small metaxylem 
elements (Text-fig. 3, D andE). 
All the actual protoxylem elements are annular or spiral, but these die 
out when traced down to the brown basal part of the petiole, although the 
1 Cf. Boodle, 1. c., PL xix, Fig. 4 . 
