CYCADOFILICES FROM THE CALCIFEROUS SANDSTONE SERIES. 819 
(Pl. IIL. fig. 16, prx.). The trace B is shown at a lower level in Pl. III. fig. 17, and 
at a still earlier stage in Pl. III. fig. 18. In this last figure the trace is just leaving 
the zone of secondary wood ; a few of the elements of the latter tissue still may be seen 
on the outer margin of the trace (PI. III. fig. 18, x). The peculiar fashion in which 
the xylem of the petiole strand is connected together is clearly shown in Pl. III. fig. 
17. The trace passes slowly outwards as we ascend, but unfortunately the soft nature 
of the inner cortex of the stem has allowed the latter to be easily crushed, and the 
petiole-traces have suffered disintegration along with the inner cortex. All that can be 
said of the petiole-trace in this region is that it certainly does not divide into small 
strands during its passage through the cortex into the free petiole. he protoxylem 
elements lie abaxially in the trace (PI. III. figs. 16 and 17, prz.). 
Opposite the point of emission of a petiole-trace from the central axis of the stem, 
the sclerotic hypoderma thins out and finally disappears. Concurrently as the hypo- 
derma dies out, the external part of the cortex becomes enormously developed until it 
becomes almost as large as the stem itself (Pl. I. fig. 4, pet. b.). In the figure shown 
the petiole base is detached from the stem, and in fact this section is cut some distance 
above the point where the trace enters the petiole. It imdicates, however, the great 
development of buttressing tissue round the petiole base. 
It will also be noticed that at this point the petiole has no sclerotic hypoderma. This 
fibrous zone, however, again appears higher up the petiole, but at that level the diameter 
of the whole rachis is much reduced. In other words, the base of the petiole is greatly 
dilated, and in that region the sclerotic outer cortex disappears. As a result of the soft 
nature of the petiole base the rachis is almost always torn from the stem or laterally 
displaced. The petiole shown in Pl. I. fig. 4 really departed opposite the gap seen at 
A in the outer cortex of the stem. The dilatation of. the petiole base occurred both on 
the upper and under sides. 
It is interesting to note that certain fern- like i impressions of Carboniferous age have 
similar dilatations where the pinnz join the rachis, and this also happens where the 
latter join the stem. (A similar type of structure may be seen in recent Marattia and 
Angiopteris pinnz where they joined the petiole.) 
Only one petiole was actually traced into the stem, but several have been followed 
until the hypoderma disappears and the trace was seen surrounded by a uniform, 
parenchymatous cortex. A similar disappearance of the sclerotic fibres has been seen 
in longitudinal section. Behind the departing petiole the sclerotic hypoderma closes in 
and ultimately fills the gap. Thus the departure of the petiole causes a temporary gap 
in the fibrous zone of the cortex. 
The trace in the free petiole is represented in PI. III. fig. 19, and although there 
is considerable crushing, one can easily observe that it consists of a continuous flat band 
of xylem with abaxial protoxylem groups. liven in the smallest branch discovered, the 
trace is continuous but with a convoluted outline (PI. III. fig. 20). In no case does 
the trace break up into a number of small strands. 
