238 Plant Life and Evolution 



which do not require light for the development of 

 their chlorophyll. In the later geological time, ac- 

 cording to this theory, the layer of clouds was grad- 

 ually dissipated, and the zonal climates, as they now 

 exist, were by degrees established. From a study 

 of the plants of the Paleozoic, especially of the 

 Carboniferous, which have left recognizable de- 

 scendants at the present time, we may conclude that 

 the climate was a moist one but not necessarily ex- 

 tremely hot. The pteridophytes, which were the 

 predominant type, at the present day reach their 

 most perfect development in the wet mountain for- 

 ests of the tropics, where the temperature is even, 

 but not excessively high. 



The Lower Plants Have Left Few Fossil Re- 

 mains. The early history of the lower plants can 

 only be conjectured. It is pretty generally conceded 

 that the simple green algae represent more nearly 

 than any other living plants the ancestors of the 

 present land flora. Whatever may have been the 

 origin of the red and brown algae, it is clear that 

 they are relatively modern forms, which are espe- 

 cially fitted for marine life. Little is known of the 

 early geological history of the fungi, but traces of 

 these are sometimes met with and there is reason to 

 suppose that they were abundant during these early 

 times. 



Both the simple green algae and lower liverworts 

 show evidences of their primitive nature, and prob- 

 ably are little changed descendants of their ancient 



