34 PROF. W. C. WILLTAMSON ON THE 



They evidently crept along the upper surface of the disk, 

 as is the case amongst ferns. 



In nearly every instance each sporangium is occupied 

 by a cluster of beautiful spores. The appearances which 

 these objects present vary according to the direction of their 

 section, as is well represented in fig. 9. At the first 

 glance, we should be tempted to infer that their exteriors 

 had been spinous ; but I have not been able to satisfy 

 myself that such has been the case. I rather conclude 

 that the appearance in question is merely the result of de- 

 fective mineralization, because, as I have already shown, 

 the outlines of all the more delicate cellular tissues of the 

 specimens are similarly masked by irregular protuberances. 

 The mean diameter of these spores is about '0037, or 

 nearly the same size as those of the Calamitean strobilus 

 of which I laid a description before this Society last year. 



The preceding description will have demonstrated that 

 this fruit is very different from any of which the internal 

 organization has hitherto been described. The differences 

 are not merely of detail, but of type. The question 

 remaining to be answered is an obvious one, viz. to what 

 plant does this fruit belong? The verticillate arrange- 

 ment of its bractigerous disks and bracts suggests the pro- 

 bability that we must seek for the parent plant amongst such 

 as have their foliage arranged in corresponding verticils ; 

 and if this law of association be a sound one, we are ap- 

 parently shut up to the three genera, Aster ophyllites, 

 Annularia, and Sphenophyllum. 



But the separation of the first and the second of these 

 genera is of doubtful propriety j at all events I have not 

 yet succeeded in discovering any definite character by 

 which the two can be distinguished. That plants of the 

 Annularian type constituted the delicate aerial foliage of 

 Calamites, appears to be established by so many inde- 

 pendent observations as to leave little room for doubting 



