32 PHYLOGENY 



tural Experiment Stations. Each state and each region, in some 

 instances even each larger farm, wants its own variety of corn, or 

 wheat, or other crops. These have to be sought out from amongst 

 the hundreds of forms generally cultivated within each single 

 botanical species. Once found, the type may be ameliorated ac- 

 cording to the local conditions and wants, but this is a question of 

 subsequent and subordinate improvement. 



Summing up the main points of these arguments, we may state 

 that artificial selection consists of two main principles, called variety- 

 testing and racial improvement. Quite the same distinction has to 

 be made in the case of natural selection, and the same double selec- 

 tion has to be acknowledged, whilst only the names have to be 

 changed. Instead of variety-testing comes the choice between ele- 

 mentary species, instead of racial improvement the adaptation to the 

 local conditions of the environment. Before going into a more de- 

 tailed discussion of this first principle of comparison, it may be as 

 well to consider that intermediate step between natural and artificial 

 selection, which is called acclimatization. 



Here the aim is given by man, but the selection is left to nature. 

 Man, however, does not only point out the object, but has also to 

 give the starting-points. The choice of the variety is directly per- 

 formed by the climate. This is manifestly shown by the slow and 

 gradual dispersion of corn in this country. The larger types are 

 limited to tropical and subtropical regions, whilst the varieties 

 capable of cultivation in the northern states are so, according to 

 their smaller size and stature. They are short-lived, requiring a 

 lesser number of days to reach their full development from seed to 

 seed. These qualities are not the result of the cultivation or of the 

 influence of the climate, since the smaller sorts are historically 

 known to have grown in tropical America at the time of Columbus 

 along with the taller types. This is especially on record in the case 

 of the forty-days or quarantine maize. Cultivation has worked in 

 this case as a sieve, or rather as a series of sieves with a diminishing 

 width of meshes, the climate allowing only the shorter-lived forms 

 to pass the meshes and to expand towards the north. Similar 

 facts are known for wheat and many other crops, and the famous 

 trials of Schuebeler in Norway have thrown a clear light upon 

 the factors of this complicated process. 



Artificial selection is a fact needing scientific and critical analysis, 

 but natural selection is a fact which we may see at work in each 

 field and in each meadow, but concerning which our real know- 

 ledge is still very incomplete. In the realm of natural selection, it has, 

 however, become customary to indulge in hypothetical considera- 

 tions. And since these have largely been applied to the side cor- 

 responding with the artificial improvement of races, I may perhaps 



