116 



obtain an affiuit}' - group by tlie direct obsen r atiou of natural affinity, as 

 ENGLER says in 2. Such groups, according to liis statement , exist 

 only in species, genera, families or in series. In other words, natural affinity 

 is to be found between one individual and another individual belonging to 

 the same species, between spacies and species belonging to the same genus, 

 between genus and genus belonging to the same family, between family and 

 family belonging to the same series ; but there is generally no phylogenetic 

 relation between series and series. Consequently, in liis system, species, 

 genera, families are, as far as his statement is concerned, arranged according 

 to their natural affinity ; while the series are not so arranged. It follows, 

 therefore, that the series are arranged, according to their degree of advance- 

 ment, or according to their simplicity or complexity, or according as they are 

 primitive or reduced. His system is locally, in this part or that, natural in 

 the sense that it denotes a certain relation of blood - kinship or a constitutional 

 resemblance ; but his system, taken as a whole, is an artificial system, the 

 series of which are arranged according to their degree of advancement, or to 

 some such idea. As for the recapitulation theory which is given by him in 

 2, as a means of determining natural affinity, it is in many cases especially 

 in plants not to be relied upon . The other experimental method given by 

 him is something that can be seen only in some few special cases. He says 

 that it is necessary to ascertain affinity through the study of the development 

 history. I think that is truly indispensable for finding the mutual relations 

 in the case of development ; but I think it is equally necessary that we should 

 take into account the resemblance in the adult stage ; the natural relation of 

 young forms is sometimes different from that of adult forms, so that the real 

 natural relation is only conceivable in its dynamic phase. He writes as 

 folio ws s) especially for the higher plants :- 



Dagegen sincl wir bei tier Feststellung iler Yerwandtsckaft koherer Sip pen 

 genotigt, auf indirektem Wege die natiirliclie Vervvandtschaft zu ermitteln, und 

 dabei leicht irrtuinlicken Auffassungen axtsgesetzt. 



1) ENGLEK, A. Erlauterungen, 1. c. p. 362. 



2) SCHOUTE, J. C. Die Stelitr-Theorie, p. 138 (P. Noordhoff Groningen, 1902). 



3) ENGLER, A. 1. c. p. IX. 



