ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 727 
evident in the petioles, as indicated by the V- or W-shaped bundle as seen in trans- 
verse section, the Dictyoxylon cortex and the peculiar emergences. Sometimes, of 
course, there is an accidental admixture of other fern petioles, 
In all cases where the petioles can be determined as belonging to Rachiopteris 
aspera we now know that we have to do with the foliage of Lyginodendron. The 
finer branches of these petioles, as was already shown in Memoir VI., are sometimes 
found in connection with portions of the compound lamina. ‘Where the latter are 
seen in surface view, some idea of the form of the leaf may be obtained. Since 
Memoir VI. was published, additional evidence has been accumulated, and the conclu- 
sion then reached is confirmed, namely, that the leaf would fall under the form-genus 
Sphenopteris of BRoNGNIART, as shown by the finely cut foliage and the acute angles 
between the veins.* It is impossible to reconstruct the leaf from the fragmentary 
remains, which are alone available : but we may take it as certain that it was a highly 
compound leaf of the Sphenopteris type. The leaflets appear to have been decurrent 
on the finer branches of the rachis. We cannot venture to refer the leaf to any known 
species of Sphenepteris, but a certain resemblance to various forms can be traced. 
(See, for example, the figures of S. Haninghausi, S. tridactylites, S. linearis, &c., in 
Broneniart’s “ Histoire des végétaux fossiles.”) 
The mere fact, that the foliage of Lyginodendron resembled that of certain Ferns is 
in itself no proof of affinity with Filices. The classical case of Stangeria is a sufficient 
warning against any such hasty inference. It must, however, be remembered that in 
the foliage of Lyginodendron we have not only fern-like form and venation, but 
also fern-like structure, whereas in the case of Stangeria a single transverse section of 
the petiole would be sufficient to prove that the plant is no Fern but a Cycad. 
Where a number of sections have been cut from the same specimen, it is possible to 
trace the repeated branching of the rachis and to observe the insertion of the leaflets 
upon its branches. The leaflets shown in section in Plate 19, photograph 7, and 
Plate 24, fig. 16 are from the series C.N. 1191-1198, and belong to leaves, the petioles of 
which, seen in other sections of the same series, present the characteristic structure of 
Rachiopteris aspera. A section of one of the petioles from this series, no doubt 
uw secondary branch, has been figured in Memoir XVIL., Plate 13, fig. 7. Though not 
actually one of those which have been traced up to the leaflets, it is identical with them 
in structure, and most probably formed part of the same compound leaf. These 
leaflets and branch petioles accompany the stem, which, as already mentioned, runs 
through the entire series. They, no doubt, belong toa lower leaf than the two which 
are seen in connection with the stem. 
The section shown in Plate 18, photograph 6,evidently passed through a portion of the 
lamina, just where the segments are beginning to separate from one another. Appear- 
ances of this kind are not uncommon in the preparations, and become readily intelligible 
on comparison with the surface view of the foliage (cf. Memoir VI., Plate 52, fig. 15). 
* See Memoir VI., Plate 52, fig. 13; also Memoir XVII, p. 91. 
