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. 



FIG. 219. 



Spkcnophyllum Daivsoni. / Obliquely transverse section of a cone, showing parts of 

 three whorls of bracts, a" = hollow axis (stele missing); l>, d= cortex of axis; e, e? = bracts 

 cut at different levels ; /"= sporangiophores, the innermost just springing from a whorl of 

 bracts, which are here coherent ; f sporangiophores in connection with their sporangia ; 

 ") g', S" sporangia of the three whorls. Xj. After Williamson, Phil. 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 



