A natomy of the Ophioglossaceae . III. 11 
explanation, and this interpretation seems justified in the light of comparison 
with the other types of trace described above. 
The main stages in the departure of one of the earlier and smaller 
traces from this rhizome are represented in PL I, Photos 14-17. The 
rhizome at this level was medullated and mesarch, though with the internal 
xylem only moderately developed. As the xylem of the trace becomes 
evident as a bulge on the stele (Photo 14), the protoxylem has an arc of 
metaxylem to the outside, and this appears almost completed on the 
adaxial side of the trace, which is still continuous with the xylem of the 
stele. Thus as the xylem of the trace becomes separate (Photo 15), it 
exhibits a complete ring of radiating rows of tracheides, the single group of 
protoxylem being in connexion with the abaxial portion of the ring, while 
a little parenchyma is present immediately internal to the protoxylem. 
The adaxial xylem at this level appears to be related to the outer xylem of 
the stele, and is in any case much more strongly developed than the inner 
xylem of the stele. At this stage the stele and leaf-trace are enclosed in 
a common endodermis and the phloem is still continuous. Photo 16 shows 
the same trace further removed from the stele. It still has a single group 
of protoxylem, the xylem being almost equally developed abaxially and 
adaxially. The interpretation given of the adaxial completion of the xylem 
in this trace is confirmed by the corresponding behaviour of the phloem, 
which is seen to form a complete tube, while the endodermis was also com¬ 
plete. A little further out (Photo 17) the small trace had passed into the 
clepsydroid stage; the endodermis and phloem were still complete. The 
xylem appeared dumb-bell shaped in cross-section, the protoxylem had 
divided into two groups, and the metaxylem elements were continuous 
across the constricted portion between the two halves. Shortly after this 
the division of the trace took place; the xylem of each half was a complete 
ring, and the phloem was complete around it. 
The departure of the larger leaf-traces from the full-sized portion 
of this rhizome was essentially similar, though the trace may be mesarch at 
its origin, and thus have some inner xylem enclosed by the adaxial extension 
of the outer xylem. One of the larger traces in the clepsydroid stage is 
represented in PI. I, Photo 18. While corresponding essentially to the 
large trace shown in Photo 6, this trace, which is at a somewhat earlier 
stage, has no evident remains of inner xylem. The two poles of protoxylem 
are clearly evident, and the adaxial arc of xylem is actually thicker than 
the abaxial portion. A little later the metaxylem develops in the centre 
of the trace connecting the abaxial and adaxial portions, and the trace then 
divides (cf. Text-fig. 8, e). In PI. I, Photo 19 the left half of this trace is 
shown with its protoxylem in two groups preparatory to the next division. 
The trace shown departing from the moderately small rhizome in 
PL III, Photo 51 agreed with those just described in having the xylem of 
