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THE AMERICAN NATURALIST 



[Vol. XLV 



that he will give us fuller data on this point in future papers 

 which are promised. 



In several cases Tower mixed three species which interbred 

 freely and left them under natural conditions for several years. 

 A careful study of the progeny in each case showed that a new 

 type arose, consisting of a complex of the characters of the old 

 types, and that this new type rather rapidly replaced every 

 other type, although some of these other types were known to be 

 quite capable of existing under the conditions of the experi- 

 ment. This would indicate that in some way the new type had 

 a distinct advantage over the other types with which it com- 

 peted for food, or possibly the repeated crossing of the types 

 was in some way inimical to all the types except the one. Ex- 

 periments of this character show that hybridization may be an 

 important factor in the development of new varieties or pos- 

 sibly new species. 



From the fact that when the same species are mixed together 

 in two places where the conditions are different, the resulting 

 type which finally wins out and becomes practically the sole 

 representative of the mixture, is different under different con- 

 ditions. Tower draws I he conclusion that the conditions sur- 

 rounding the germ cells at the time of fertilization "profoundly 

 modify the behavior and the relationships of the characters en- 

 tering into the crosses." This conclusion seems hardly justified. 



from what we know of the behavior of Mendelian characters 

 and that these types would naturally bear different rela- 

 tions to the environmental conditions offers apparently a 

 much simpler explanation of the reason for the survival of 

 the one type under one set of conditions and another type 

 under another set of conditions. It seems hardly necessary 

 to assume that the conditions existing at the time of the fertil- 

 ization of the egg determine the characters which were to result 

 from the fertilization to explain this particular phenomenon. 



Subsequent investigation of these new types of mixed origin 

 showed that in all eases they occasionally produced individuals- 

 different from the general population but which in all cases ex- 

 hibited characters which were present in the original parents 

 of the complex mixture. Tower repeatedly compares this phe- 

 nomenon to the phenomena which de Vries observed in (Eno- 



