CHAPTER IV. 



REACTIONS AND PRODUCTS IN INTERSPECIFIC CROSSES. 



I have had to deal with many interspecific crosses, and these I have uniformly 

 treated as follows: Species freshly introduced into the laboratory were first 

 acclimatized to the conditions of the breeding-quarters, which were the average 

 conditions of the breeding-season of their native habitat. It was found that 

 3 to 6 generations will suffice to fully adjust any wild stock to the conditions of 

 the breeding and experimental rooms. In this way I eliminate in crosses 

 between species many of the disturbing effects of conditions in the material, 

 " adaptation " to one especial complex, and thus make the crosses the product 

 of the constitution of the organisms as completely as is possible at present. I 

 was forced to do this, because I found that species direct from diverse habitats 

 in nature were giving most irregular results that were difficult of repetition and 

 analysis. 



It may be objected that this treatment is abnormal, and that it is productive 

 of change in the species ; but none has been found, and only those species are 

 used for these interspecific crosses that are able to completely adjust themselves 

 to one environmental complex. The mere fact that they are not able to do so is 

 all the indication needed to exclude them from crossing experiments where 

 effects of environment are to be eliminated. It has been my experience that 

 species so brought into the same set of conditions do not change; do not lose 

 any capacities or characteristics, are not weakened, and when returned to the 

 original specific native environmental complex are able to take up at once the 

 original routine without effort or waste of individuals or energy. 



METHODS OF CULTURE. 



The most essential factor in the successful breeding of animals of the kinds 

 that I have used — phytophagous Coleoptera, Lepidoptera, and Hemiptera — is 

 the constant presence of a plentiful supply of perfectly fresh and normal food, 

 under conditions such that the normal transpiration of both plant and animal 

 can go on, and with adequate air-movement to remove from the vicinity of the 

 organisms the air contaminated by the products of respiration and transpira- 

 tion. It has been my experience that unless this is attained in a complete and 

 constant manner trouble will inevitably follow in the cultures — disease, 

 weakened vitality, with the probable loss of the culture and termination of the 

 work. 



In all experiments it has been my first care to have the organism, regardless 

 of the kind upon the specific living plant, which is the normal food for the 

 species in the location from which the material originally came. The plant 

 must not only he alive, but in the usual actively growing condition, as in nature, 

 so that the organisms may have an adequate, normal, and hygienic food supply. 



90 



