62o STUDIES IN FOSSIL BOTANY 



species (e.g. Sphenophyllum Dawsoni, p. 101) the in- 

 creased number of leaves has affected the stele itself, each 

 of its angles being double. When the leaves are further 

 segmented, a further forking of the bundles takes place 

 within the cortex, and it appears indisputable that the 

 numerous leaves of such a species as S. myriophyllum 

 represent the segments of a few deeply divided original 

 appendages. In the Calamariaceae, on Lignier's view, 

 the same process has gone further, the increased 

 dimensions of the stem involving a corresponding 

 multiplication of the leaves and of the bundles in the 

 stem. In cases like the axis of Calamostachys, we have 

 a clear analogy with Sphenophyllum in the fact that each 

 two bracts receive their vascular supply from the same 

 axial bundle, while in Palaeostachya vera the axial 

 bundles are themselves duplicated, forming evident pairs 

 (p. 65). It certainly appears highly probable that the 

 small and numerous whorled leaves of the Calamariaceae 

 may have arisen, as in the Sphenophyllales, by the 

 subdivision of a smaller number, with corresponding 

 anatomical changes. That the leaves were originally 

 compound or much cut is rendered probable by the 

 presence of such divided leaves in the early fossils 

 Archaeocalamites , and more especially Pseudobornia, the 

 leaves of which, when found isolated, were actually 

 taken for the fronds of a Fern. 



In anatomy, the Sphenophyllales, with their solid 

 protostele, appear to be clearly more primitive than the 

 Equisetales, which in all cases have a pith and distinct 

 vascular bundles. The anatomical gap between the 

 two classes appeared a very wide one, until it was 

 partly bridged by the discovery of centripetal wood in 



