336 PLANT-BREEDING 



headings. One case embraces the widely-spread species, 

 the other those with a Hmited area. For the first it is instantly 

 clear that at best only one of their numerous habitats can be 

 the spot where they have originally been produced. To all 

 their other locahties they must have been introduced, and, if 

 we do not consider collective forms but pure and elementary 

 types, tliis must have happened without changing their 

 original characters. Now, the question arises, which 

 locaHty is their native one? Observation teaches that 

 in almost all instances there is no evidence of a difference 

 between this one and the others. Therefore, it is simply 

 impossible to answer this question in any case with sufficient 

 certainty. It is generally assumed that in the center of the 

 whole dominion of a plant its native station is concealed, 

 but this is only a hypothesis, resting on no observational 

 basis. Quite as well some species might have spread in one 

 direction only, and then their native spot would lie at the 

 very end of their realm. Granting that we cannot recognize 

 this original center of cHspersion, we may turn to a discussion 

 of the large majority of the observed localities. Some plants 

 are evidently better fitted for certain stations, while others 

 prefer different life-conditions. The large group of the 

 evening primroses may afford instances. In Cahfomia 

 only one large-flowered species is met with in the wild 

 state. It is the CEnothera Hookeri which occurs on waste 

 places along roads and railroads, and may even be seen here 

 and there in the parks. It is evidently suited to the climate of 

 CaHfornia, but its dispersion in Arizona and other neighbor- 

 ing states makes it very probable that it is no real native 

 Cahfornian, but has only been introduced. In tliis case no 

 single one of its quahties can possibly be explained by the 

 demands of its present environments. 



Other species of evening primroses give further proofs. 

 Two of them were introduced into Europe more than a 



