1 90 SELECTION. 



and want to see in "pure lines" the ultimate constituents of 

 all species. 



Blaringhem, in his lectures at the Sorbonne went so far 

 as to speak of "pure lines" of guinea-pigs and of sheep. 



Lotsy has attempted to identify species in general with 

 pure lines, and, parting from the observation that pure lines 

 have no gt-^etic variability, defines species as groups of organ- 

 isms which are devoid of genetic variability. 



Contrasted to the marked polymorphy of such compound 

 groups of very pure species, and of compound groups of veg- 

 etatively reproducing lines, clones, the relative conformity 

 to type of the multitude in allogamous species is very striking. 



Variability in such species of allogamous organisms may be 

 relatively high, and yet we find on analysis that there does 

 exist a common type to which the multitude conforms, and 

 from which aberrant individuals depart in one or in a few 

 characteristics, but seldom in very man}'. Within such species 

 random mating counteracts the continuity of typical groups. 



There is a very great difference between the kind of species 

 which we observe in the autogamous plants, small groups, de- 

 void of any Potential variability, and the sometimes highly 

 variable species in the allogamous organisms. And yet, they 

 are both the smallest permanent units. It is absolutely nec- 

 essary to recognize in plants as well as in animals common, 

 comparable units. If Systematics had to do without the spe- 

 cies-conception, or if under the term species were understood 

 different things in different groups of organisms, systematics 

 would return to the pre-Linnean chaos. 



For this reason any attempt, such as Lotsy's, to restrict the 

 use of the term species to some special kind of species, which 

 has no equivalent in other divisions of the organic world, 

 should be discouraged. 



In certain plants there exist small species, which are wholly 

 devoid of variability of a genotypic nature. But this purity is 

 not the essential thing, which makes these groups species. It 

 is the result of the very severe isolation, produced by 



