The Practical Conception of Species. 391 



ical and critical arguments for this ])racticc. 11ic word 

 stirp would perhaps correspond most closely to the ( ier- 

 man word Sippc,^ although this word has been empl(jyed 

 by various authors in a different sense.^ At any rate it is 

 most desirable to make some distinction of this kind, and 

 Belli's suggestion might well form the foundation of 

 such. Rut questions of nomenclature have little interest 

 in this discussion and I prefer to leave the task to others. 



Wt may now proceed to the practical delimitation of 

 the conception of species. 



Descriptive biology wants a definition, independent 

 of the results of hybridization ; in its commonest form it 

 is based on the absence or presence of transitional forms, 

 as was explained in the first part of this volume. Groups 

 of individuals which are connected together bv transitions 

 are considered to belong to the same species. The limits 

 between species correspond to gaps in the series.'' \\'ith- 

 out some such convention the description of species oc- 

 curring in collected material would be impossible ; and this 

 method has been emplo3^ed by the best systematists since 

 tlic time of DeCandolle. It is only when direct exj^eri- 

 nients can be carried out that the prol)lcm can be dealt 

 witli in a different wa}^ 



1^wo difficulties, however, present themselves, wliich 

 I shall now briefly deal with. In the first place, exactly 



^ Die Mutationcn tiiid die Mufafiouspcn'odcu hri drr Ruisfchuui: 

 dcr Artcn. Leipsic, Veit & Co., 1901, p. 14. 



" C. CoRRENs, Schcinhare Ausnalimen von dcr McndrVschcu Spal- 

 hin^^srcgrl fiir Basfardc, Bcr. d. d. bot. Ges.. ]()02, \'«)l. XX. Part V 

 p. 170. See also the same author in Bcr. d. d. bot. (ics.. 1901. Vol. 

 XTX, p. 77, note i. and his Monograpliic dcr Maisbastordc. p i. and 

 Von Wett.steix, Cnmdciigc dcr gcograf^hisch-niorf^hologischcn Mr- 

 tliodc dcr PHauzcnsystcmatik. 1898. p. .v 



"Sec, for instance, Anncc hiologiquc. TV. 1898. p. 470: V. 1800. 

 p. T,77 and elsewhere. Also Borrad.mlle. On Crustacians. lyoi, p. iQ^: 

 rrKiSEnACH, Dic J'cgcfafioii dcr Erdc nach Hirer klinmlisclicn Auord- 

 niiiig. 1872. p. 9. and so forth. 



