SAPORTA'S WORLD OF PLANTS. 



453 



abundance. In the Cambrian and Silurian, fossils are found that are 

 differently interpreted, and in which at present some think they see 

 algte. The famous bilobites, so abundant at the base of the Silurian, 

 appear also to have been algae of very great height. Finally, certain 

 marine plants, as those that are represented by Fig. 3, are connected 

 with a type of algs^ so marked that it is difficult to mistake them. 



Fig. 3.— Primordial Marini: Plants: 1. Spyrophyton of Hall (Silurian of America). 



sonites Forbesi (Goepp) (Silurian of Ireland). 3. Chondrites Jruticulosus (Goepp). 



Many of these plants are undeniably linked with more modern types, 

 of which they bear the generic form, and prove that this primordial 

 flora is not really separated from that which followed it. We can 

 even affirm that certain Silurian algoe have had a duration so prodi- 

 gious and a tenacity of character so pronounced that their last direct 

 descendants were living in the European seas in the middle of Tertiary 

 time. As to primordial land-plants they are excessively rare, and 

 those that we have gathered seem to demonstrate that in the Silurian 

 epoch to which they belong the vegetable forms represented types 

 that we encounter in subsequent formations, and that are characteris- 

 tic. In Fig. 4 are shown those that M. Lesquereux observed in the 

 Upper Silurian of the United States. Among them are the Psilophy- 

 ton, which disappeared with the Devonian, and the ambiguous charac- 

 ters of which approached at the same time the ferns by the Hymeno- 

 phyles, the Lycopodiaceae by Psilotum, and the Rhizocarpes by Pilu- 

 laria. 



