Artificial and Natural Selection 803 



vious lecture I have detailed the rapid increase 

 of the wild-oats in certain years, and described 

 the experiments of Risler and Rimpau in the 

 running out of select varieties. The agency is 

 always the same. The preferred forms, which 

 give a larger harvest, are generally more 

 sensitive to injurious influences, more dependent 

 on rich manure and on adequate treatment. 

 The native varieties have therefore the advan- 

 tage, when climatic or cultural conditions are 

 unfavorable for the fields at large. They suf- 

 fer in a minor degree, and are thereby enabled 

 to propagate themselves afterwards more rap- 

 idly and to defeat the finer types. This 

 struggle for life is a constant one, and can 

 easily be followed, whenever the composition 

 of a strain is noted in successive years. It is 

 well appreciated by breeders and farmers, be- 

 cause it is always liable to counteract their 

 endeavors and to claim their utmost efforts to 

 keep their races pure. There can be no doubt 

 that exactly the same struggle exempt from 

 man's intrusion is fought out in the wild state. 

 Local races of wild plants have not been 

 the object for field-observations recently. Some 

 facts however, are known concerning them. On 

 the East Friesian Islands in the North Sea the 

 flowers are strikingly larger and brighter col- 

 ored than those of the same species on the 



