150 MENDELISM chap. 



disposed to grant, and this has sometimes led him to 

 expostulate with the latter for cutting off the supply. 

 On the newer views, however, this difficulty need not 

 arise, for we realise that the origin and establishing of a 

 new form may be a very much more rapid process than 

 has hitherto been deemed possible. 



One last question with regard to evolution. How far 

 does Mendelism help us in connection with the problem 

 of the origin of species ? Among the plants and animals 

 with which we have dealt we have been able to show 

 that distinct differences, often considerable, in colour, 

 size, and structure, may be interpreted in terms of Men- 

 delian factors. It is not unlikely that most of the vari- 

 ous characters which the systematist uses to mark off 

 one species from another, the so-called specific characters, 

 are of this nature. They serve as convenient labels, but 

 are not essential to the conception of species. A sys- 

 tematist who defined the wild sweet pea could hardly fail 

 to include in his definition such characters as the pro- 

 cumbent habit, the tendrils, the form of the pollen, the 

 shape of the flower, and its purple colour. Yet all these 

 and other characters have been proved to depend upon 

 the presence of definite factors which can be removed by 

 appropriate crossing. By this means we can produce a 

 small plant a few inches in height with an erect habit of 

 growth, without tendrils, with round instead of oblong pol- 

 len, and with colourless deformed flowers quite different 



