286 PROCEEDINGS OF THE AMERICAN ACADEMY. 



maining organisms, which either by reason of their large size or imper- 

 fect condition of preservation cannot be so satisfactorily subjected to 

 microscopic investigation. It is apparently beyond question that both 

 Pila kentuckynna and P'lla scotica represent the spores of vascular 

 cryptogams. This conclusion has been reached from the study of the 

 numerous thin sections which are readily prepared by the methods em- 

 ployed in the present investigation. Abundance of material makes it 

 clear that the bodies which have been interpreted as colonial gelatin- 

 ous Algae, in reality represent certain planes of section through the 

 rough-coated spores of vascular cryptogams. When the structures in 

 question are cut in favorable planes and of sufficient thinness, it be- 

 comes clear that the algal semblances represent tangential sections of 

 the rough external surface of spores of vascular plants. The real na- 

 ture of the supposed Algae is further made clear by their possession of 

 the triradiate ridge characteristic of tetrahedral spores. Moreover, in 

 certain instances the plane of section has been observed to pass at once 

 through the plane anterior faces and the rough, rounded external one. 

 Further, in serial sections, which may be prepared by the methods de- 

 scribed above, the putative Algae may be seen to present at once the 

 alveolar appearance which has been interpreted as indicating algal 

 affinities and the form and triradiate ridges, which clearly indicate 

 their identity as spores of vascular cryptogams. If any further evi- 

 dence were needed as to their true nature, it would be furnished by 

 their occasional occurrence in actual tetrads, a condition which, in con- 

 nection with the other data derived from the study of thin sections, 

 makes it impossible to regard them as anything else but spores. 



In the case of the larger supposed Algae the case is not so clear, on 

 account of the distorted and often swollen condition in which they 

 occur, as well as by reason of the difficulty of interpreting objects of 

 greater dimensions by means of thin sections. The writers who have 

 studied the various supposed algal structures of Paleozoic coals are, 

 however, agreed in the conclusion that they all belong to the same 

 category. I am myself entirely in accord with this opinion. The view 

 of the uniformity of the organisms under discussion is further strength- 

 ened by the fact that gradations in the condition of preservation occur 

 in the case of the larger Pilas and of Reinschia, which show clearly in 

 the condition of best preservation the greatest resemblance to Pila 

 keMuckyana and Pila scotica. Unfortunately it was such badly pre- 

 served species as Pila bihractensis and Beinschia austndis which were 

 first studied microscopically. 



Another very important argument against the algal character of the 

 characteristic structural constituents of so-called boghead coals is 



