Kidston.—Note on the Petiole of Zygopteris Grayi , With 453 
towards the opening rather confirms the opinion already stated as to 
the branch possessing a solid protostelic structure, though here again 
the preservation of the specimen leaves the matter in doubt. 
The petiole trace seen at Fig. 6 possesses all the essential characters 
of Zygopteris di-up sit on, Williamson. It is of course much smaller than the 
trace in the fully developed petiole ; that seen at Fig. 6 only measuring 
1*7 mm. in a direction parallel with the cross-bar, while the measurement 
of the same portion of the petiole trace in the type specimen of Z. di-upsilon 
is 4-75 mm. It is, however, an ascertained fact that the petiole trace 
increases in size in its passage outwards, and does not seem to attain its 
full dimensions even in the immediate base of the free petiole. 
That the petiole shown at Fig. 6 and still contained within the cortex 
of Zygopteris Grayi cannot be an immature condition of the petiole which 
Williamson identified as Zygopteris bibractensis , Renault, and which has 
now been distinguished as Z. bibractensis var. Westphalica by Dr. Paul 
Bertrand, 1 is seen from its narrow straight bar and the long thin arms, 
scarcely incurved, and without any indication of the external band of small 
tracheae on the outside of the arms, which is so distinctive a feature in the 
Z. bibractensis type of petiole. The very much incurved arms and curved 
cross-bar of this latter species are also absent from the petiole trace of our 
specimens. On the other hand, all the characters of the petiole trace found 
in the cortex of Z. Grayi are identical with those of Z. di-ttpsilon. 
It might be pointed out that the petiole which Williamson figures 
on PI. I, Fig. 4 of his Memoir xv, is referable to Zygopteris di-upsilon , and 
this I think was his opinion, for he refers to it as ‘a similar Zygopteroid 
petiolar bundle ’ to that he has described in the cortex of Z. Grayi? 
The morphology of the so-called ‘ axillary shoot ’ which I regard 
simply as a branch must shortly be considered. 
Stenzel was the first to observe this so-called ‘axillary shoot’, 3 but 
later it was also recognized by Williamson, who described it as a ‘ circular 
aberrant organ ’ which he regarded as a branch, and this is the view that 
has been generally accepted, and the leaf-trace has been considered to arise 
from a division of the ‘ axillary shoot ’ into two unequal parts. It is thus 
described by Dr. Scott: ‘ As we follow the leaf-trace outwards through the 
cortex, we find that it divides into two strands, of very different form, both 
lying on the same radius. The outer of the two strands is the foliar bundle, 
which is continuous with the external side of the original triangular strand, 
while the inner strand is destined for the axillary shoot.’ 4 
In regard to the ‘ axillary shoot ’ in the Hymenophyllaceae, Tansley 
says: ‘ The stem-like structure of the strand below the junction of the leaf 
1 P. Bertrand, 1 . c., p. 73. 2 Williamson, 1 . c., p. 157. 
3 Stenzel, Die Gattung Tubicaulis Cotta, pp. 35-6, 1889. 
4 Studies in Fossil Botany, 2nd ed., vol. i, p. 311, 1908. 
