202 SPECIES AND VARIETIES. 



of a species in the midst of which they live, constitute a variety, 

 whereas individuals differing in a group of characters from 

 hitherto described species — constitute a new species. In both 

 cases systematists have for a long period had an opinion, differ- 

 ing radically from that of the geneticians, and the later ge- 

 netic evidence all points to the fact that the systematicians 

 have been right. 



In this connection, the matter of denomination should re- 

 ceive some attention. It would seem, to a great many authors 

 as if it were greatly a matter of personal taste whether a given 

 group of specimens should be divided into two, or twenty, or two 

 hundred species. What should be our standpoint? All the evid- 

 ence goes to show, that species are realities, not only convenient 

 groups made up at will. Therefore the number of species into 

 which to divide a drawer of skins should be definite. The na- 

 ture of the material should have a great influence. In autog- 

 amous plants excessive polymorphism is the rule. Here the very 

 nature of the material makes species out of every tjTpe. Every 

 plant is isolatec^ from random crossing with others, and in a 

 few generations its descendants will be all homozygous, will 

 have a total potential variability — zero. Such material will 

 therefore consist of a host of pure species. Here the "splitter of 

 species" certainly is in his right absolutely. Nevertheless, the 

 whole group, the combination of a whole group of species has 

 certain quaUties in common with one species in the allog- 

 amous organisms. If on a pertain day there are fifteen hundred 

 different species of oats, every one of these may have a total 

 potential variability zero, but the whole of the fifteen-hundred 

 combined have a very great Total potential variability, and 

 this total potential variability has a tendency to reduce itself. 

 In such a group of species new ones are constantly being pro- 

 duced as a result of occasional crossing, but on the other hand 

 all the time some of the species are becoming extinct. To keep 

 intact a collection of several himdred species of wheats, it is 

 necessary, carefully to conserve a plant of each number for 

 seed every year. This is not only necessary to keep the species 



