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 type. Every 

 plant is isolated 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 qualities in common with one species in the allog- 

 amous organisms. If on a certain 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 hundred 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 



