Eeactions and Peoducts in Interspecific Crosses 163 



numerous accentuations and developments of these, with few apparently new 

 characters. There have been in domestication crossings without number, con- 

 trol, and perhaps all possible combinations, so that it may be probable that the 

 initial impetus given to primitive man to breed and utilize some of these then 

 wild organisms came from this same sort of initial disruption of two originals, 

 by chance giving combinations pleasing to the savage fancy, so that they were 

 perpetuated with his crude breeding operations, and come down to later periods 

 in culture. The initial cross would in all probability not be intentional, but the 

 product of breeding of the tamed with the surrounding wild forms, as is known 

 to be the case in savage or barbarous establishments. 



One point further is of interest in this cross, namely, the fact that the initial 

 Fi and F^ arrays are on the whole tlie most complex, and that thereafter the 

 reactions of the products of the primary cross are all increasingly towards 

 simplicity, as the lines are reduced progressively to homozygous-acting biotypic 

 strains, between which crosses give only the most orderly and monotonous 

 Mendelian reactions and products. This experience is also in harmony with the 

 crossings of domesticated plants and animals, to which, thus far, the majority 

 of the orderly and fully analyzed Mendelian operations are confined. Thus, the 

 20 types shown in plate 18 are, when crossed in biotypic condition, productive 

 of monohybrid or dihybrid reactions, rarely of trihybrid, while the huge 

 majority in the tests thus far are of the simpler types. In many respects this 

 cross of decemlineata and oblongata shows the difference between species or 

 groups in nature and the purified races of cultivation in the complexity of the 

 natural, the homogeneity of the cultural, in reactions that test their gametic 

 constitution ; but in both there is no difference in the basic principle of reaction. 

 This is the essential point and one upon which attention is directed in the 

 summary at the close of this chapter. 



LEPTINOTARSA DECEMLINEATA X LEPTINOTARSA MULTIT/ENIATA. 



The crossing of these two species is complicated and can best be presented 

 under two headings — the crossing of the natural species and the crossing of 

 biotypic lines. These species, especially rmiUitceniata, are in natural conditions 

 complex in their constitution, and when they are crossed the ensuing F^ and Fj 

 arrays are diverse, depending upon the original composition of the stocks used. 

 In some of the earlier chapters it has been shown that for muUitceniata the 

 composition is complicated by differences in form, pronotal pattern, sports, and 

 other means of gametic complexity. As a result the crossing gives in each set 

 of matings differences and arrays depending upon the stocks used. I have for 

 the purposes of this analysis purified the parent stocks used, and then utilized 

 them in crosses in the determination of the relations between these two species 

 when crossed. I shall describe the results of crossing the biot}'pic lines first, 

 and then the general reactions when the crosses are made between the stocks 

 as a whole. 



CROSSING OF BIOTYPIC UNES IN DECEMLINEATA AND MULTIT>tNIATA. 



The simplest and standard cross between these two species is that made 

 between a biotypic line of pronotal pattern biotype 7, mean form-index, mean 

 yellow-white pronotal color, and mean pronotal color, each with the pure non- 

 variable larval characters proper to each species. Two biotypes of this sort are 



