EVOLUTION 197 



they exhibit. Even though one cannot grow each member 

 of such a population under identical conditions as to nutri- 

 tion, the plants impress one as if each had been cut out 

 with the same die. Qualitative characters such as color 

 show no greater variation, as far as human vision may 

 determine, than descendants of the same mother plant 

 propagated by cuttings. Further, in certain characters 

 affected but slightly by external conditions, such as flower 

 size, the sexually produced population not only shows no 

 greater variability than the asexually produced popula- 

 tion, but it shows no more than is displayed by a single 

 plant. Yet one must remember that in such a test, the 

 seeds necessarily contain but a small quantity of nutrients 

 and for this reason the individual plants are produced 

 under somewhat more varied conditions than those result- 

 ing from cuttings, hence it would not have been unreason- 

 able to have predicted a slightly greater variability for 

 the sexually produced population, even though the coeffi- 

 cient of heredity of both were the same. Similar, though 

 less systematic, observations have been made on wheat — 

 an autogamous plant almost as satisfactory for such a 

 test as Nicotiana — ^with practically identical results. 



One is justified, then, in claiming there is experi- 

 mental evidence to. show that sexual reproduction in 

 itself is no more than an exact equivalent of asexual re- 

 production in the matter of an heredity coefficient. Biit 

 is this also true for germinal variation? We believe it is. 

 Variations similar in size and kind arise both in asexual 

 and in sexual reproduction, but it cannot be maintained 

 they occur more frequently in the latter. There are insects 

 in Oligocene amber apparently identical with those of 

 to-day, proving constancy of type to be possible under 



