CHAPTER V. 

 REACTIONS AND PRODUCTS IN INTERSPECIFIC CROSSES. 



In Chapter IV, data and the analysis of the crossing of species from nature 

 were given, showing interesting possibilities for the production of irregularities 

 in the laboratory, as well as potentialities for the production of natural groups 

 capable of continuation and independent existence in nature. 



Clear indication was presented that the gametic complexes behaved as units 

 in the production of the gametes in F2 and of the purity of the types found in Fj 

 as determined by genetic testing and biometric measurements. Between these 

 some interchange of factorial groups was observed, as well as the formation of 

 combinations that were permanent and stable. These latter were, however, 

 capable of dissociation, showing the manner of their production and the nature 

 of their composition. In this chapter is presented further data derived from 

 the crossing of species from nature. 



LEPTINOTARSA DIVERSA X LEPTINOTARSA DECEMLINEATA. 



The cross between these two species is difficult to make, and out of many trials 

 I have thus far obtained two series that gave progeny that would breed on into 

 F2 and beyond. Many of the trials have given juvenile stages, fewer adults, 

 only two lines that were able to breed through several generations. 



The species differ in almost all of their attributes, not only in the color and 

 pattern characters presented in all of the stages of each form, but also in the 

 form-index, the rates of ontogentic development, in the food that each is able 

 to utilize, as well as in many other characters. Perhaps the chief difference 

 that is of interest in this cross is the specificity of the food-relation presented 

 and which enters into the results of the cross. L. decemlineata normally feeds 

 upon Solarium rostratum, S. tuberosum, S. nigrum, etc., but will eat some few 

 of the woody types, but none of them with success. L. diversa will not eat the 

 first-named types ; as far as experience goes it feeds only upon the woody types 

 that are its food in nature (-S^. liegerii, S. chrisotrichum, 8. lanceolatum, etc.). 

 So specific is this relation that L. diversa will starve before it will eat potato or 

 S. rostratum, while L. decemlineata will eat the food of L. diversa when forced, 

 but never thrives thereon, and in all instances perishes by continued use of the 

 L. diversa food. 



In the crosses between these two species I have used only materials of L. decem- 

 lineata that were pedigreed and came from my oldest line, and of L. diversa 

 also only pedigreed stock. Between these two species I have made over 200 

 trials, always in reciprocal pairs, and thus far only two matings of L. decem- 

 lineata female X male L. diversa have given lines capable of any analysis, and 

 these were both in all respects precisely alike. The crosses were made under the 

 conditions of the breeding-quarters, to which both species had been fully 



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