DOMAIN OF EVOLUTIONARY HYPOTHESIS 131 



of the present organisms, compared with those of 

 palaeontology which we have discussed above, there 

 are deduced, as it appears necessarily, the following 

 conclusions : 



1. The generally accepted and usually corresponding 

 separation of all the recent organisms into a number 

 of groups shows that there are really certain gradings 

 existent. We are in the great majority of cases not 

 long in doubt whether a plant, for instance, belongs to 

 the Ferns or Equisetums or Angiosperms. 



If difficulties arise, they do so almost always on 

 account of peculiarities, which we may justifiably 

 consider as due to secondary ' adaptive phenomena ' 

 (specialization or regression). The study of the repro- 

 ductive relations, with which in most cases are asso- 

 ciated other characteristic features, finally determines 

 the systematic position. 



2. All certain results of palaeontology indicate that 

 the still surviving higher systematic categories were 

 retained also during the geological periods, so that 

 we can class the greater part of the fossil forms with 

 the recent ones in the same system. 1 



Of clear transitions between Pteridophytes, for 

 instance, and Gymnosperms nothing can be said ; what 



1 To class together fossil and recent forms as equivalent and closely 

 associated orders, families, etc., is the endeavour of all the newer text- 

 books for instance, the great joint work of Engler and Prantl : Die 

 naturlichen Pflanzenfamilien. See also Lotsy: Vortrage uber botanische 

 Stammesgesckichte (so far 2 vols.) ; E. Stromer v. Reichenbach : 

 Lehrbuch der Paldontologie (so far 1 vol.) ; F. Broili in the new edition 

 of the Grundzuge der Paldontologie of Zittel (so far 1 vol.). The great 

 work of Zittel and Schenk is likewise entirely based on these methods. 



K2 



