22 BIOLOGICAL LECTURES. 



vigor during that time is evident from the nature of the 

 remains which appear in later formations, and the first well- 

 defined occurrence of terrestrial forms in the Siluro-Cambrian 

 or Ordovician would go far to show that plants passed through 

 their amphibious stage at least as early as the Huronian, thus 

 preceding the corresponding phase in the progress of animal 

 life by a very long period of time, since in the latter case this 

 change was not effected until the later Carboniferous and 

 Permian. That the Eozoic and early Palaeozoic must have 

 witnessed the development of high types of plants is abun- 

 dantly evident from the abrupt occurrence, in the Upper Silu- 

 rian and Lower Devonian, of gigantic marine algae, of which 

 there are no equally large representatives in later formations ; 

 while in the Devonian, also, there occur for the first time plants 

 which are comparable in their reproductive structures with the 

 more modern Pilularia, and a brief consideration of the leading 

 features of some of these plants may assist us in gaining a more 

 complete appreciation of the statements already made. 



In his Old Red Sandstone, Hugh Miller described certain 

 peculiar discoid bodies found in the Devonian rocks of Scotland 

 at Blairgowrie, Myreton, and other localities. In 1831 these 

 objects were described by Dr. Fleming under the name of 

 Parka decipiens, and both by him and subsequent observers, 

 during a period of sixty years, they were regarded as represent- 

 ing the spawn of Mollusca, the eggs of frogs or other animals, 

 but always without suspicion that they might have been derived 

 from plants ; and it was reserved for Dawson and Penhallow, in 

 1 89 1, to prove clearly their vegetable nature. These bodies 

 consist of carbonized discs, or their impressions, about 5-6 mm. 

 in diameter and grouped in oval masses varying in size from 

 3.5x5.3 cm. to 13x20 mm. In their more complete forms 

 these masses show the presence of an external covering, 

 and there is also some indication that a stalk may have been 

 present. No stems or leaves can with certainty be considered 

 to belong to these bodies, since as yet no organic union between 

 such organs has been observed, but there is reason to believe, 

 from the associated structures, that they belonged to plants with 

 a creeping stem and upright leaves, while the recent finding 



