66 
A: G. Tansley. 
relic of the time when, according to our basal hypothesis, the 
structure of the fronds of ferns was but little differentiated from 
the structure of their stems. 
Fig. 16. Stauropteris oldhcimia. Part of the axis whose main strand is 
represented in Fig. 15. Two tetrarch branch-traces are seen in the cortex 
with a small monarch trace to one side, x 20. 
Fig. 17. Stauropteris oldhamia. Xylem of the strand of a large axis in 
the act of giving off branch traces : evidently an earlier stage of the condition 
shown in Fig. 16. Scott Collection, x 20. 
Fig. 18. Stauropteris oldhamia. Tetrarch, triarch and monarch branchlets 
of the frond. Scott Collection, x 20. 
The four masses of xylem making up the “ cruciate ” strand of 
the axis of Stauropteris, the two side pieces (which may be regarded 
as four wings) of Zygopteris, and the wings of the C-type are to be 
regarded as specialised parts of the rachis-strand developed to 
supply the demands of the branches or pinnae ; or, to put the same 
fact in another way, as the sympodial bases of the branch-traces. 
