ASPECTS OF KINETIC EVOLUTION 395 



same time unusual vegetative vigor, analogous, in all probability, 

 to the stimulation of energy of growth which appears in normal 

 crosses and in prepotent new variations. Though no experi- 

 ments are known to have been made with the idea of such a test 

 directly in mind, the indications are that results of mutation and 

 hybridization might prove in the same species almost identical, 

 for many so-called false hybrids do not appear to be the results 

 of a genuine and effective interbreeding, but seem rather to 

 involve an approach to the phenomenon of artificial partheno- 

 genesis, somewhat similar to the parthenogenetic development 

 through chemical and mechanical stimuli, described by Loeb 

 and others. The two nuclei of the supposed parents of the 

 false hybrid do not appear to have united and combined the 

 parental qualities, since the progeny shows no definite indication 

 of the traits of one of the supposed parents, either in the first or 

 in subsequent generations. The facts discovered by Guyer in 

 sterile hybrid pigeons, that the parental chromatin elements 

 remain separate and do not undergo a normal mitapsis, illus- 

 trates the possibility of false hybrids, especially in plants and 

 in lower types of animals where parthenogenesis can take place. 

 Such an abnormal and inadequate method of fertilization would 

 explain extensive variations of the progeny, which well deserve 

 to be called false hybrids. Nor is it unlikely that the same 

 explanation may be found to apply to variable hybrids, even 

 when they share the characters of the parents. The indications 

 are that in different cases there are all possible gradations in 

 the extent and efficiency of the combination of the parental ele- 

 ments, from that which affords mere stimulation to that which 

 gives a fully intermediate result. 



It does not follow, however, that the combination is normal 

 or complete when the first generation is intermediate. The first 

 generation may be intermediate under two nearly opposite con- 

 ditions, as already noted. Crosses are intermediate when the 

 parental elements are thoroughly congruous. Their combina- 

 tion merely restores a normal condition of symbasis, that is, 

 provides a normal amount of diversity of descent. The first 

 generation of hybrids is also intermediate when the parental 

 elements are very diverse and antagonistic. Hybrids which 



