FROM THE LOWER COAL-MEASURES. 63 
Affinities. 
Sutcliffia is referred to the family Medullosex on account of the general organization 
of the leaf-bases and petioles, the course of the leaf-trace bundles, the tendency to 
dialystely shown by the formation of the subsidiary steles or meristeles, and the 
histology both of the vascular and cortical tissues*. The genus differs from the other 
members of the family in the stem having a single main stele in a central position and 
in the concentric structure of the foliar bundles. The former character is unique in the 
family, for although Colpoxylon has a single stele in part of the stem, its irregular 
outline suggests a local fusion of the two or more steles that occur in other parts of the 
specimen +. Concentric petiolar bundles have not been described in any other member 
of the family (apart from Sutclifia Williamsoni) In Steloxylon Ludwigii, however, 
according to Count Solms-Laubach’s interpretation of its structure, branches of the 
steles, instead of single bundles, enter the petioles from the stem 1, so there would 
appear to be a possible analogy in this respect with Sutcliffia, though the complexity of 
the stem-structure in Steloxylon forbids any further comparison. 
The question of the homologies of the parts of the vascular system in Sutcliffia has 
been discussed above (p.53). As there are no features pointing to reduction from a 
more complex structure, the view is taken that the main stele represents the original 
protostele, such as we find in Heterangium, while the meristeles constitute a subsidiary 
peripheral system, differentiated to meet the demands of the megaphyllous foliage for an 
elaborate vascular supply. Thus we may, if we will, interpret the structure of Suteliffia 
as dialystelic, but it is peculiar in the fact that the original central stele still remains 
dominant. I am not aware of any analogous case, either fossil or recent, among 
Cycadofilices or Ferns. Where we find concentric cylinders, or zones in the stems of 
Ferns, the central strand is found to be subsidiary, arising from a more peripheral 
vascular zone §. This depends on the fact that throughout the Fern-series dialystely is 
attained by the expansion of the original stele into a tube (siphonostele of Jeffrey), 
which becomes broken up by the leaf-gaps.  Swteliffia appears to represent the unique 
case of dialystely without siphonostely. Analogies may no doubt be found in species of 
Selaginella |, but in these microphyllous forms the conditions are 80 widely different 
that the comparison cannot be profitably pursued. I do not desire, however, to press 
the dialystelic interpretation of Sutcliffia too strongly; there are no absolute distinctions 
in anatomy, and the meristeles of Swtclifia may be regarded as transitional between 
leaf-traces and “steles.” In trying to determine the position of the new genus among 
the Medulloseze we must take into account the characters of the petiole, as well as those 
of the stem. As regards the petiole, the main feature is the concentric structure of the 
vascular bundles; the presence of xylem-parenchyma is another point cof interest, 
though of secondary importance. In both respects the foliar bundles retain more of a 
* Scott, 1900, p. 374. § Gwynne-Vaughan, 1903; Tansley, 1905, 
+ Renault, 1896, p. 301, pl. 67. || Harvey-Gibson, 1894. 
1 Solms-Laubach, 1897, p. 197. x 39 
