36 



COENOPTERIDACEAE 



[CH. 



The inferences that may be drawn from Table I are these. First, it 

 appears that where the size of the stele is small the protostele has a solid 

 core of xylem {Botryopteris). Where the size is larger, as in Diplolabis, the 

 xylem maybe differentiated internally: where it is larger still {Ankyropteris) 

 it is not only differentiated but its cylindrical form may be changed, giving 

 the fluted character, though this is not always proportionate to actual size 

 {Clepsydropsis australis). In still larger stems {Cladoxylon, Asterochlaend) 

 the deeply stellate stele is reached, still with internal differentiation. But 

 this is not always so, for in the most ancient of them all there is a deeply 

 stellate outline of the xylem, but no internal differentiation {Asteropteris). 

 As regards the ratio of the diameter of the stem to that of the stele it appears 

 that in the largest the stele may expand in higher degree than the stem as 

 a whole {Asterochlaena, Asteropteris): but there does not appear to be any 

 constant ratio to absolute size {AnkyropteiHs). The table further brings 

 prominently forward the fact that Botryopteris, which has commonly been 

 regarded as a very primitive type, is far the smallest in the actual dimensions 

 of stem and stele, a fact which accords well with the theoretical position. 



Applying the same method of analysis to the petioles of the Coenopteri- 

 daceae a parallel series of results is apparent, and as the petioles are known 

 in a larger number of examples the results are the more impressive .and 

 reliable: 



Table II. Coenopterid Petioles 



