264 Gwynne- Vaughan . — On the Anatomy of 
All the strands hitherto described belong to the typical leaf-trace curve 
referred to above, but the additional internal strands that occur in the basal 
pulvinus of Kaulfussia are also to be found in the same region of Archangio - 
pteris ; they are, however, more feebly developed and less regular in their 
behaviour. In all the leaves examined, and it probably holds true for the 
leaves of the plant in general, the internal strands invariably arise as branches 
on the inside of the strands of the abaxial region of the typical curve, and 
they always pass upwards across the internal ground-tissue to fuse with 
the median adaxial strands of the curve before the top of the pulvinar 
region is reached. Only two of these strands were found in any one 
petiole, and almost immediately after their origin they fuse together to 
form a single one with its protoxylems on the abaxial side (cf. Figs, it and 
12). After passing upwards for a short distance they become separate 
again, and finally fuse with the two terminal strands of the typical curve 
(cf. Figs. 13 and 14). In one case a single strand only was given off, which 
passed obliquely across and fused with the terminal strand on its own 
side. 
The internal strands seem to join on indifferently to either end of the 
incurved terminal strands. In one case the same internal strand fused 
first with one end of the terminal strand, and then, after separating off 
again, finally fused up with the other. Sometimes the internal strands are 
connected with their respective terminal strands by a short suture before 
they themselves come into actual contact. 
All the vascular strands in the petiole above the basal pulvinus belong 
to the typical horseshoe-shaped curve. The ends of the horseshoe are 
curved deeply inwards so that the two terminal strands take up a more or 
less internal position (Fig. 15). They remain separate from each other 
throughout the greater part of the petiole, but in certain regions they fuse 
together to form a single large internal strand with the protoxylem facing 
adaxially (Fig. 16), just as in Kaulfussia. In these two plants, therefore, 
an important distinction has to be made between these more or less included 
strands of the typical curve and the internal strands that occur in the 
basal pulvinus which have quite a different origin. In other Marattiaceae, 
however, the internal strands of the pulvinus are continued into the upper 
part of the petiole. For instance, in a form of Marattia fraxinea that 
I examined there were, at a point just above the basal pulvinus, two separate 
concentric rings of internal strands, and also a single strand occupying the 
centre of the ground-tissue. In the upward direction these strands gradually 
disappear in precisely the manner that might have been anticipated from 
the behaviour of the internal strands in the basal pulvinus of Kaulfussia 
and A rchangiopteris. First of all the central strand fuses with one of the 
median adaxial strands of the inmost ring. Then those of the inmost ring 
successively fuse with the adaxial strands of the ring next without, which 
