V ascular System of Matonia pectinata. 
507 
Fig. 15. Diagrams of a 
series of transverse sections 
through the node of a tri- 
cyclic rhizome. A. Inter- 
node shortly before node; 
dorsal protoxylems dividing 
up preparatory to formation 
of leaf- trace. Second cylin- 
der with one dorsal proto- 
xylem. Third with none. 
B. Second cylinder with 
three protoxylems. C. Two 
dorsal protoxylems of 
second cylinder have divid- 
ed to form four. Proto- 
xylem of right lateral loop 
branching. D . Second 
cylinder in connexion with 
right lateral loop. Two 
protoxylems in lateral loop. 
E. The two protoxylems 
of right lateral loop in con- 
nexion with a branch from 
right outer protoxylem of 
dorsal group of second 
cylinder. F. Two central 
protoxylems of dorsal group 
of second cylinder now in 
compensation-tongue, which 
has filled gap in outer cylin- 
der. Right outer proto- 
xylem remains in edge of 
gap of second cylinder. 
Two protoxylems in left 
lateral loop of leaf-trace. 
G. The two protoxylems ot 
left lateral loop in con- 
nexion with a branch from 
left outer protoxylem 
originally derived from 
dorsal group of second 
cylinder (now in edge of gap of second cylinder), 
seen in median dorsal position in outer cylinder, 
protoxylem in edge of gap. 
left lateral loop 
Two median dorsal protoxylems of this group 
II. Protoxylems of left lateral loop have joined 
edge of gap, second 
cylinder 
) mid-dorsal band 
\ first cylinder 
edge of gap, second 
cylinder 
N.B. These figures are taken from a series through a very young node in which the protoxylems 
are the only parts of the vascular tissue differentiated. The main arch of the leaf-trace, which 
would be attached between B and C , is not yet laid down, the forward extensions of the lateral 
loops (seen in C to F) being the only part of the attachment of the trace to the stele as yet formed. 
The protoxylems of the left lateral loop (that nearest the apex of the stem and therefore the 
youngest) are not yet formed in C to E, but only in F, where the loop is in immediate connexion 
with the upstanding flange on the edge of the gap of the second cylinder. 
