RESULTS OF PAL.EONTOLOGICAL RESEARCH 49 



It therefore happens that the appearance of the 

 organisms is constantly changing, and forms appear 

 which are new and specialized, i.e. adapted to quite 

 definite modes of existence, nutrition, habitats, etc. 

 But in no case does the entire change, which the organ- 

 isms finally show in comparison with the original form, 

 go so far that offspring and ancestors can no longer 

 be united within the same systematic class. Generally 

 the totality of the descendants and ancestors, despite 

 all ' evolution/ still form the same order, the same 

 family, and sometimes even the same genus. ' Genea- 

 logical trees ' or pedigrees which ignore all systematic 

 classification are simply illusory. 



The ' evolutionary series ' (pedigrees) of some organ- 

 isms, the course of which may be followed more or less 

 without hiatus, never present such considerable devia- 

 tions from each other that the new forms (species and 

 genera) must be arranged l in separate natural families/ x 



B. RESULTS OF PAL^OBOTANY (EVOLUTION OF THE 

 PLANT WORLD). 



With the history of the evolution of the plant world 

 we are less acquainted than with that of the animals. 

 This is due to various causes. 



In order that organisms may be preserved in a 

 fossil form they must be withdrawn from the corrod- 

 ing influence of the atmosphere, particularly the free 

 access of oxygen. This happens generally, and is best 

 effected, by deposition of mud, sand, or even of other 



1 Daperet-Wegner : Die Umbildung der TierweU, p. 250. 



