THE GEOLOGICAL HISTORY OF PLANTS. 



many palaeo-botanists have referred to the Marsiliacce, 

 though, like other Palaeozoic Acrogens, it presents com- 

 plexities not seen in its modern representatives. 8. pri- 

 mcevum of Lesquereux is found in the Hudson River 

 group, and my 8. antiquum in the Middle Erian. Be- 

 sides these, there are in the Silurian and Erian beds 

 plants with verticillate leaves which have been placed 

 with the Annularis, but which may have differed from 

 them in fructification. Annularia laxa, of the Erian, 

 and Protannularia Harlcnessii, of the Siluro-Cambrian, 

 may be given as examples, and must have been aquatic 

 plants, probably allied to Rhizocarps. It is deserving of 

 notice, also, that the two best-known species of Psilophy- 

 ton (P. princeps and P. robustius), while allied to Ly- 

 copods by the structure of the stem and such rudimentary 

 foliage as they possess, are also allied, by the form of 

 their fructification, to the Rhizocarps, and not to ferns, 

 as some palaeo-botanists have incorrectly supposed. A 

 similar remark applies to Arthrostigma ; and the beautiful 

 pinnately leaved Ptilophyton may be taken to represent 

 that type of foliage as seen in modern Ehizocarps, while 

 the allied forms of the Carboniferous which Lesquereux 

 has named Trochopliyllum, seem to have had sporocarps 

 attached to the stem in the manner of Azolla. 



The whole of this evidence, I think, goes to show that 

 in the Erian period there were vast quantities of aquatic 

 plants, allied to the modern Rhizocarps, and that the so- 

 called Sporangites referred to in this paper were probably 

 the drifted sporocarps and macrospores of some of these 

 plants, or of plants allied to them in structure and habit, 

 of which the vegetative organs have perished. I have 

 shown that in the Erian period there were vast swampy 

 flats covered with Psilophyton, and in similar submerged 

 tracts near to the sea the Protosalvinia may have filled 

 the waters and have given off the vast multitudes of 

 macrospores which, drifted by currents, have settled in the 



