ANATOMY 



401 



The leaves appear both from, their size and from their structure 

 to have been the assimilating organs, while the axis took little part in 

 that function. Their parenchymatous tissue was, however, mechanically 

 strengthened by bands of sclerenchyma. The vascular strands given off 

 at the nodes usually branched within the cortex of the stem into strands 

 which passed out as the veins of the leaf, though in some cases a single 

 strand entered the leaf. 



FIG. 217. 



Splienophyllutn iusigne. Transverse section of rather young stem, showing triangular 

 primary wood with a canal at each angle, marking the protoxylem, then secondary 

 wood, remains of phloem, and the primary cortex showing two of the furrows. X about 

 30. From a photograph, Phil. Trans. W. and S. Will. Coll., 919. (Block from Scott's 

 Studies in Fossil otany.) 



The strobilus of Sphettophyllum was constructed on a plan similar to 

 that of the vegetative shoot, with slight structural differences, and with 

 the additional fact that the spore-producing parts are present. These took 

 the form of sporangiophores, resembling in their main features those of 

 other sporangiophoric Pteridophytes. The most obvious differences between 

 the strobilus and the vegetative shoot are that the internodes are shorter, 

 and the leaves, which are elongated as before, frequently show a distinct 

 webbing below. The result is that the whole cone appears externally as 

 a compact body, with the sporangiophores very adequately protected till 

 mature (compare Fig. 215). The various fossils described under the 

 generic name of Sphenophyllum show differences of detail in the number 



2 c 



