SPORE-PRODUCING MEMBERS 403 
interesting from the fact that its strobilus is not a strictly definite one 
(Fig. 221). The number of the leaves in the whorl of the vegetative 
region is not constant: six to eight have been observed by Mr. Kidston. 
Fic. 219. 
Sphenophyllum Dazvson?. Obliquely transverse section of a cone, showing parts of 
three whorls of bracts. a@”=hollow axis (stele missing); 6, @=cortex of axis; ¢, e’ =bracts 
cut at different levels ; /=sporangiophores, the innermost just springing from a whorl of 
bracts, which are here coherent ;_/ =sporangiophores in connection with their sporangia ; 
& g, g" =sporangia of the three whorls. x7. After Williamson, PA72 Trans. Will, 
Coll., 1049 B. (From Scott’s Studies in Fossil Botany.) 
The branching of the leaves is variable, and even the two halves of one 
leaf may be unequal: the sporophylls are especially narrow as compared 
with the foliage leaves. The strobilus is characterised by the shorter 
length of the internodes, though this is variable also in the vegetative 
region: a gradual transition occurs at the limits of the fertile tract, but 
without any sudden alteration of the size or form of the leaf: the sporo- 
phylls stood out from the axis just like the ordinary foliage leaves, but 
