DEPARTMENT OP BOTANICAIv RESEARCH. 



67 



tion profitable. 24 large cages and the inclosure for pedigree-work are 

 located on the adobe soils of the Santa Cruz Wash at the foot of Tumamoc 

 Hill; 8 cages are located on this hill near the laboratory and on the same 

 level, and 3 in the gulch opening on the west side of the hill. 



Eight species and races of Leptinotarsae are now carried in these cultures 

 at Tucson, in all 20 different cultures, which will hibernate during the winter 

 of 1909-10. The conditions of the arid foresummer of 1909 retarded the 

 growth of the food-plants and the breeding activities of the beetles, but the 

 general progress of the series is considerably better than was anticipated 

 even with favorable conditions. 



Certain interesting results, partly new and in part confirmatory of general 

 principles derived from my Mexican cultures, have been derived from these 

 cultures of 1908-09. The behavior of newly introduced species and races 

 continues to confirm the result stated in an earlier publication, that the 

 response is immediate if at all, and that the introduced form does not remain 

 suspended or uncertain in its behavior, but reacts at once in one way or 

 another. This reaction may be equilibration with or without structural or 

 physiological modification, or it may be extinction through inhibition of the 

 reproductive powers, and only very rarely are the adults themselves elimi- 

 nated by changed conditions. 



A novel result was attained in cultures of two highly variable stocks of 

 Leptinotarsa midtitceniata and L. oblongata, wherein changed conditions of 

 existence with large and strong populations gave decreased variability of a 

 most striking kind. This was most remarkable in the highly variable species 

 L. miiltitcBniata, which was reduced to less than 15 per cent of the ancestral 

 variability and the whole culture moved to a new mode and mean. 



A series of experiments was begun at Tucson in 1908, in which L. decem- 

 lincata from Chicago, L. midtitceniata from Mexico City, and L. oblongata 

 from Cuernavaca, Mexico, which interbreed freely, were placed in a cage at 

 Tucson. These species may be crossed with each other in pedigree cultures 

 with results that may be interpreted to conform to the Mendelian law, if 

 one so desires. They interbreed freely at the places mentioned, and out of 

 the combination five forms result in the first hybrid generation : L. oblongata 

 forms (A); L. oblongata-decemlineata forms (B) hybrid; L. decemlineata 

 forms (C) ; L. decemlineata-multitceniata (D) forms hybrid intermediates; 

 L. viultitceniata forms (E). The three pure forms or dominant forms. A, C, 

 and E contain pure matings and hybrid dominants. The intermediate forms 

 B and D are clearly intermediate first-generation hybrids, but at Tucson the 

 intermediate hybrid between L. oblongata and L. niultitcuniata does not ap- 

 pear. The cultures at this place gave the following in 1908-09; parent 

 generation included 2 males and 2 females of the three species : 



First generation . . 



Males . . . 



Mated females 

 Second generation 

 Third greneration* 

 Fourth generation 



* Sample count. 



