23 
A natomy of the Ophioglossciceae. Ill. 
the great development of accessory xylem (x. 2 ) to the sides of the gap 
which has just closed, and also the first indication of the development of an 
arc of xylem connecting the accessory xylem over the region of the gap. 
In Photo 28, which represents the structure a little further forward, this arc 
of accessory xylem (marked x.o. in the upper part of the figure), destined 
to continue as the outer xylem of the branch, is fully developed, consisting 
of short reticulate tracheides. Passing into the concavity of the arc of 
accessory xylem is seen a group of smaller spirally thickened tracheides 
(x.i.) which are continuous above with the inner xylem of the branch stele. 
The fact that these tracheides of the inner xylem appear to pass out from 
the region of xylem which was left doubtful at the preceding level (cf. 
PI. II, Photos 27 and 28) adds probability to the view that here also the 
inner xylem was continuous between the main stele and that of the branch, 
though it is not possible to state this with certainty, as in the case of the 
first branching specimen. Comparison may be made between the condition 
shown in Photo 28 for the second branch, with that shown in Photo 23, and 
in Text-fig. 4, F, G, for the first branch. 
Beyond this level the base of the branch stele bends away from the 
line of the axis of the main stele, as has already been described. The 
swollen base of the branch stele with its xylem distinguishable into outer 
xylem (continuous with the arc of accessory xylem) and inner xylem, the 
origin of which has been referred to above, is still in continuity with the 
accessory xylem of the stele in Text-fig. 6 , D. Still further out, the stele of 
the branch, which has been seen in Text-fig. 5 to be followed longitudinally, 
narrows. The connexion between the basal transitional region and the 
narrow stele is shown in PI. II, Photo 29, which shows the distinction 
between the outer xylem of the branch and the tracheides of the inner 
xylem, forming together with parenchyma a kind of ‘ mixed pith ’; the 
photograph further shows how the isodiametric tracheides of the accessory 
xylem are continuous with the elongated tracheides of the branch, where 
it has grown in length by the activity of its proper apex. The next section 
of the series (Text-fig. 6 , E) is mainly of interest as showing the departure 
of the first leaf-trace from the branch stele, the direction of which was 
indicated in Text-fig. 5, l.t} The xylem of the base of the branch now 
appears completely separate from that of the main stele, but the other 
tissues of the branch still show continuity. In the last section (Text- 
fig. 6, F) all sign of the branch has gone, the stele of the rhizome is complete, 
save for the next leaf-gap in relation to the trace which has just left the 
cortex, but it is noteworthy, as already stated, that the zone of accessory 
xylem is still well marked, and only ceases to be developed after this 
leaf-gap has closed. 
If the actual connexions of the vascular system of the two branches to 
their respective steles be compared, an essential agreement will be found 
