3 I 2 WILLIAM LAWRENCE TOWER. 



In 1906, 1907 and 1908 these cultures were allowed to shift 

 for themselves, and the food plants were nearly swamped by 

 immigration into the glade of plants from the surrounding Rain 

 Forest ; in fact, the whole culture was allowed to engage in a most 

 desperate struggle for its existence. As far as the beetles were 

 concerned, this was simply a struggle for food. In 1908-1909 

 the inroads which had been made by other plants had so reduced 

 the number of Solanums that the food supply was inadequate. 

 During these years, however, no trace of the signaticollis type 

 has ever appeared. In 1908, material of the undecimlineata type 

 was taken from this culture to Chicago, and there subjected to 

 the tests of pedigree analysis, but without any trace of the 

 signaticollis form appearing. In both experiments, however, at 

 Praesidio and at Cuernavaca, the resulting materials were different 

 in the gametic make-up from the original species. Superficially, 

 these stocks could not be told from the natural species, but when 

 used as the basis of experiment under control conditions, it was 

 found that there resulted a difference in the behavior of the 

 subsequent hybrid generations, clearly indicating a change in the 

 gametic constitution of these groups of individuals. 



Other experiments involving the same two species are in prog- 

 ress, under desert conditions at Tucson, Ariz. 



Competition Hybridization Experiments Between L. decem- 

 lineata, L. oblongata and L. multitceniata. 

 A series of experiments, more conclusive and under better 

 conditions, has been carried on, using three species: L. 

 decemlineata, L. oblongata and L. multitceniata. Of these, in 

 nature, L. decimlineata is limited solely to the United States 

 and southern Canada; L. multitceniata entirely to the southern 

 portion of the plateau of Mexico, and L. oblongata to the Balsas 

 Valley and the Oaxaca-Guerrero Highlands. These species inter- 

 cross freely under experimental conditions and present the follow- 

 ing contrasting characters for consideration. The general ground 

 color of the larvae of L. decemlineata is wine red, that of L. oblon- 

 gata and L. multitceniata chrome yellow. L. decemlineata and L. 

 multitceniata have two rows of spots along the side in the larvae. 



