216 THE EVOLUTION OF PLANTS 



in Sphenophyllum fertile both alike were fertile, 

 developing as sporangium-bearing organs. 



There can be no doubt that the Sphenophylls 

 were related to the Calamites. Apart from 

 general resemblances, such as the jointed stems 

 and whorled leaves, the 

 structure of the spo- 

 rangia and the organs 

 which bore them was 

 practically identical in 

 members of the two 

 groups. It should be 

 mentioned that in the 

 Sphenophylls, so far as 

 we know, all the spores 

 "* were of one kind, but 

 sometimes there was 

 considerable variation 

 in the size of the 

 spores, and abortive 

 spores were present. 



Fig. 25. Sphenophyllum It has been suggested 

 Dawsoni. Diagram of cone, in .1 . . i 



longitudinal section; (ox) that a tendency 

 axis; (br) bracts, some in sec- towards the formation 



SR r .CM r^ f tw ** f s p res 



sporangiophores; (sm) spo- may thus be indicated 

 rangia. From Scott, Studies. (see above , p . 207). 



There are two important differences (apart from 

 size) between the Sphenophylls and the Calamites. 



ax 



