54 



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 

 Khizocarps, 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. 



c 



gd?. 



AX 



y^X 



OX 



Fio. 16. — Sporangitm {Protosalvinia). A, Sporangites BraziKmsis^ 

 size. AX, Same, magrnifled. b, Sp. oiloba, natural size, o, 

 macrospores. d, Spore-eases of Salvinia natans. dx. Same, 

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



^ntttui-al 

 Detached 



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-^ 



