CHAPTER VI. 



FOSSIL PLANTS. 



"Vegetation of early Geological periods. — Disappearance of groups 

 of Plants. — The evolution of plants corroborated by Geological 

 evidence. 



OWING to the minute size and delicacy of structure 

 of many of the early types of plant life belonging 

 to the Algae and Fungi, these would hardly be expected 

 to occur in a fossilized condition, nevertheless, certain 

 microscopic types of fungi, closely allied to the fungus 

 causing the potato disease at the present day, have been 

 detected in sections of fossil wood belonging to the Car- 

 boniferous period, and the microscopic group of Algse 

 called diatoms also occur in immense numbers in various 

 formations dating from the Carboniferous, where two 

 species occur that have passed down to the present day 

 without undergoing the minutest observable change in 

 any direction, and still exist in considerable numbers. 

 This at first sight appears directly opposed to the theory 

 of evolution, without, however, in reality being so, and 

 only proves that a change of environment is at least a 

 very important factor in promoting those modifications 

 of structure that eventually become sufficiently marked 

 to constitute what we term new species or groups. One 

 important feature clearly shown in the geological record 



