The Practical Conception of Species. 589 



can hope to arrive at a conception of species wliich shall 

 be both in accord with the facts, and justified by experi- 

 ment. 



Of course, I am well aware that the experiments 

 which have been carried on up to the present are by no 

 means sufficient and that much remains to be done. Nu- 

 merous experiments in hybridization are necessary before 

 they can serve as a foundation for systematic distinctions. 

 But the leading principle in these researches must always 

 be the attempt to determine the elementary characters. 



§ 4. THE PRACTICAL CONCEPTION OP SPECIES. 



Both collective and elementary species are called spe- 

 cies ; and this twofold significance of the word has thrust 

 its roots so deeply into the history of descriptive biology, 

 tliat it will probably never be wholly eradicated Lix- 

 NAEUS himself confused the two ideas; and whilst some 

 readers derive from the study of his works the conviction 

 that in his mind the collective forms were the true spe- 

 cies,^ others come to a different view of his attitude, and 

 believe that in formulating the conception of species, he 

 was considering the real units of the system. - 



The fundamental conception from which almost all 

 investigators start, is that species are the only real enti- 

 ties.-'^ As to what these entities are, opinions dilkT. 

 ''On ne pent pas douter," says De Caxdolee. "que Ic 

 groupe appele espece par Tillustre Suedois ne fut. dan^ 



' Sec Vol. I, p. 20. 



" S. Bet.t.t. Observations critiques sur la rcalite des esf>eees eti 

 iialurc an point dc vuc de la systeniatique des z-egetaux. 1901. 



' C Nagelt. Entstehung und Begriff der naturhistonsehen Art. 

 1865. p. 31. 



