59 
Zygopteris Grayi of Williamson. 
The conception of the meristele as a leaf-trace keeps the Zygopteris 
Grayi type in line with all the other Zygopterideae, and is in agreement 
with all the facts, as, for example, with the § phyllotaxis. 
On the branch interpretation, the arrangement of the appendages would 
not be a phyllotaxis at all, but a caulotaxis — a system of dichotomies 
in which the successive smaller limbs followed a % divergence— a strange 
phenomenon for which we should be puzzled to find an analogy. Also, 
the branch theory would compel us to assume that the main stem was 
leafless, or restricted to scale-leaves (like a Finns), while the foliage-leaves 
were limited to the lateral branches or smaller limbs of the dichotomy. 
All these are sufficiently improbable assumptions where Ferns are con- 
cerned, and, even without the evidence of the Shore specimen, would almost 
drive us to accept the simple and intelligible view that the leaves are borne 
directly on the stem. 
What then are we to make of the axillary branch ? Although it certainly 
does not give rise to the leaf-trace it must undoubtedly have some effect on 
the structure of the latter in the basal region. In the case of Williamson’s 
later specimen especially, the effect is very marked, disguising to a con- 
siderable extent the leaf-trace character of the meristele ; it led to the whole 
organ being regarded as the stele of a branch. In the Shore specimen, on 
the other hand, as we have seen, the leaf-trace characters predominate 
throughout, and the presence of an axillary shoot is only indicated in the 
meristele by a slight adaxial bulge and by the median island of internal 
xylem. It is not even certain that the latter is necessarily connected with 
the axillary stele, for a very similar central island appears in the leaf-trace 
of Z. corrugata , which has no axillary stele (P. Bertrand, ’09, PI. XII, 
Fig. 88) ; in this case, however, it soon dies out. 
We may, if we like, regard the axillary stele as f adherent ’ to the 
adaxial side of the leaf-trace, but this is a mere phrase and throws no new 
light on the facts. 
The analogy with the axillary branching of the Hymenophyllaceae has 
been often insisted on (see especially Boodle, ’00, p. 487), and appears to 
be a very close one. In the recent family the axillary shoot is sometimes 
abortive (Chambers, Tl), and possibly, as Stenzel thought, this may also 
occur in Zygopteris , though certainly not as a rule. 
Axillary branching also takes place occasionally in Ophioglossaceae 
(Botrychium, Holle, V 5, p. 313, Taf. Ill, Fig. 4 ; Helminthostachys , Gwynne- 
Vaughan, ’02). Judging from sections kindly shown me by my friend 
Prof. W. H. Lang, F.R.S., there seems no doubt that here also there is 
a decided analogy with the fossil forms. 1 It is interesting that the axillary 
branching occurring in Zygopteris should find its parallel in two recent 
1 Professor Gwynne- Vaughan’s suggestion that the axillary organs which he found in Helmintho- 
stachys were rudimentary branches appears to be fully confirmed by Professor Lang’s observations. 
