ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 913 
which it was at first regarded as identical. Subsequently the species C. Cusheana 
was established for the heterosporous form.* 
Apart from the heterospory, there are some slight differences between the species. 
While in C. Binneyana both bracts and sporangiophores stand out exactly at a right 
angle with the axis, in C. Casheana they seem to have been placed rather obliquely, 
sloping slightly upwards. Further, in a tangential section of ©. Casheana, passing 
through the sporangia, the bracts are beginning to separate from one another ; 
whereas in similar sections of C. Binneyana, they form a perfectly coherent disc. It 
appears then, that the coherent portion of the bracts did not extend so far in the 
heterosporous as in homosporous species (see Plate 74, photograph 15). These 
differences, however, are very slight, and it is certainly a most striking fact that 
species so nearly alike in general characters should exhibit so important a physiological 
distinction as that between homospory and heterospory. 
A second specimen of C. Casheana, obtained from the Strinesdale Pit, Saddleworth, 
has more recently been discovered. Two sections have been cut of the strobilus, the 
one tangential (Plate 74, photograph 15), the other transverse (photograph 16). The 
former shows parts of three verticils of sporangiophores; the highest and lowest. 
verticils show macrosporangia only ; the intermediate whorl also contains a single 
microsporangium, which is borne on the same sporangiophore with three macro- 
sporangia (photograph 15, also Plate 82, fig. 38). The relative size of the microspores 
and macrospores agrees exactly with that in the former specimen, 7.¢., the diameter of 
the macrospores is, on the average, just three times that of the microspores. The 
absolute dimensions of both are perhaps a trifle smaller than in the original specimen, 
but the difference is insignificant. 
The transverse section of this strobilus (C.N.1588, Plate 74, photograph 16 ; Plate 82, 
fig. 36) is very interesting. The section passes through macrosporangia only ; 
the pedicels of the sporangiophores are cut obliquely, which agrees with their 
ascending direction, as shown in the other specimen.+t 
The structure of the axis is extremely well shown, and agrees exactly with that of 
C. Binneyana. The axial cylinder, or stele, is of the obtusely triquetrous form, and 
has a somewhat sclerotic pith. The arrangement of the vascular bundles agrees 
with that of the homosporous species. Traces of the protoxylem-groups are found 
in the usual position, namely within irregular gaps on the inner side of the vascular 
bundles, of which there seem to have been six altogether. 
The most interesting point, however, is that ‘the axis has a well-marked zone of 
secondary wood (see fig. 36); the radial arrangement of its elements is such as to 
leave no doubt as to their origin. We thus find in this specimen the direct proof 
that secondary growth in thickness co-existed with heterospory : in other words the 
* WitiiaMson, in ‘ Report of the British Association for 1886.’ 
+ O.N. 1024. See Wittiamson, loc. cit., Part XI., Plate 54, fig. 24. 
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