64 



THE GEOLOGICAL HISTORY OF PLANTS. 



water. More especially they resemble the sporocarps of 

 the genus Salvinia. This fact opened up an entirely 

 new field of investigation, and I at once proceeded to 

 compare the specimens with the fructification of modern 

 Rhizocarps, and found that substantially these multitu- 

 dinous spores embedded in the Erie shales may be re- 

 garded as perfectly analogous to the larger spores of the 

 modern Salvinia natans of Europe, as may be seen by 

 the representation of them in Fig. 16. 



® 



AX 



yix 



DX 



Fig. 16. — Sporangites {I^otoaahinia). a. Sporangites Brasiliends, natural 

 Bize. AX, Same, magnified, b, Sp. biloba, natural size, c, Detached 

 umerosporos. n, Spore-cases of 5fl«'»«trt iiatans. dx. Same, magnitied. 

 E, Shale with sporangites, vertical section, highly magnified. 



Ill 



The typical macrospores from the Erian shales are 

 perfectly circular in outline, and in the flattened state ap- 

 pear as discs with rounded edges, their ordinary diameter 

 being from one seventy-fifth to one one hundredth of an 

 inch, though they vary considerably in size. This, how- 

 ever, I do not regard as an essential character. The 

 edges, as seen in profile, are smooth, but the flat surface 

 often presents minute dark spots, which at first I mis- 



