70 CARNEGIE INSTITUTION OF WASHINGTON. 



known product of a complex ancestry, exhibit no more range of vari- 

 ability than do either of the parental types, and are found to continue 

 undisturbed through many generations, or if disturbing factors are 

 brought to bear upon a portion of the stock, that portion of the line 

 only exhibits the type of the behavior which de Vries has characterized 

 as "mutation." 



These experiments thus show in concrete fashion how a type of 

 behavior that may be immensely important in the production of new 

 varieties and elementary species may be produced. It is a known 

 fact in human history, and it is equally certain in other organisms, 

 that there have been repeated, almost constant, intermingling 

 of different types, and this intermingling of different types may well 

 be the basis of stem-forms which give here and there those sporadic 

 types which are called "sports." It hkewise gives a naturalistic 

 aspect to the process which de Vries described and makes it at once 

 open not only to experimental investigation, but quite possibly of 

 some value in operations of economic importance. 



The modifications of the antennse which are of generic or subordinal 

 value in Leptinotarsa signaticollis, produced as the result of experi- 

 mental desert conditions, continue to show their permanency, and in 

 the cultures at Chicago have gone even further than indicated in last 

 year's report. It is desired to attempt to reproduce this sort of 

 structure in the experiments at Tucson, but thus far it has not been 

 possible to get L. signaticollis to become acclimated to the Tucson 

 conditions sufficiently to begin the operations necessary for the 

 production of this character. 



The many types of cultures now at Tucson, especially those of 

 hybrid composition, all indicate positively that materials of hetero- 

 zygous composition stand a far better chance of survival and of 

 becoming established in a new, rather adverse habitat, and are 

 distinctly stronger and better able to withstand the conditions of 

 the environmental complex at Tucson than any one of the parental 

 types. This is especially well shown in a culture introduced at Tucson 

 in the first hybrid generation as Fi heterozygotes from a cross of L. 

 signaticollis X L. diversa. Neither of the parent species breeds with 

 any considerable success thus far at Tucson. The hybrid culture 

 breeds with success, is able to pass the winter as heterozygotes and 

 also as extracted individuals of both parental types, and this is 

 especially interesting in view of the fact that the winter of 1912-13 

 at Tucson and the dry fore-summer of 1913 have been the most 

 severe in the history of these experiments, thus indicating that in 

 heterozygous and F2 extractive material there is increased possibility 

 for change and rearrangement, and for the production of adjustments 

 of one kind or another between the organism and its environment, 

 such that the organism may come to persist in the new habitat. 



