THE BRIAN OR DEVONIAN FORESTS. 



69 



Bpecies which I have had an opportunity to examine, 

 Salvinia natans of Europe perhaps presents the closest 

 resemblance. In this plant groups of round cellular 

 sporocarps appear at the bascv of the floating fronds. 

 They are about a line in diameter when mature, and are 

 of two kinds, one containing macrosporcs, the other mi- 

 crospores or antheridia. The first, when mature, hold a 

 number of closely packed globular or oval sporangia of 

 loose cellular tissue, attached to a central placenta. Each 

 of these sporangia contains a single macrospore, perfectly 

 globular and smooth, with a dense outer membrane (ex- 

 hibiting traces of lamination, and showing within an 

 irregularly vacuolated or cellular structure, probably a 

 prothallus). I cannot detect in it the peculiar pores 

 which appear in the fossil specimens. Each macrospore 

 is about one-seventieth of an inch in diameter when ma- 

 ture. The sporocarps of the microspores contain a vastly 

 greater number of minute sporangia, about one two-hun- 

 dredths of an inch in diameter. These contain disc-like 

 antheridia, or microspores of very minute size. 



The discs from Kettle Point and from the Ohio black 

 shale, and from the shale boulders of the Chicago clays, 

 are similar to the macrospores of Salvinia, except that 

 they have a thicker wall and are a little less in diameter, 

 being about one-eightieth of an inch. The Brazilian 

 sporocarps are considerably larger than those of the mod- 

 ern Salvinia, and the macrospores approach in size to 

 those of the modern species, being one seventy-fifth of an 

 inch in diameter. They also seem, like the modern spe- 

 cies, to have thinner walls than those from Canada, Ohio, 

 and Chicago. No distinct indication has been observed 

 in the fossil species of the inner Sporangium of Salvinia. 

 Possibly it was altogether absent, but more probably it is 

 not preserved as a distinct structure. 



With reference to the microspores of Salvinia, it is to 

 be observed that the sporocarps, and the contained spores 



