EXPERIMENTS IN HYBRIDIZATION AND TEMPERATURE. 28? 



compare them with the types, which in the cold and warm ex- 

 periments were proved undoubtedly to be the direct results of 

 these moderate high and low temperature influences, we find that 

 a considerable number of the latter actually exist as local or 

 seasonal forms, or that the variation lies in the line of the 

 phylogenetic development of these forms, backwards or forwards. 

 This is quite the reverse of the aberrations ; they diverge entirely 

 from such lines of development, and — this seems to be the 

 second peculiarity of the character — do not vary on the lines 

 of the normal line of the phylogenetic development of the 

 species. 



It was certainly not the sole purpose of these heat and frost 

 experiments to obtain aberrations, but by this means to follow 

 up two questions of scientific interest, and if possible to answer 

 same. 



Firstly, what factors in nature cause the appearance of 

 aberrations, which as to their appearance in free nature and 

 characters form such obscure problems ? And secondly, are 

 these new forms ; is the aberrative coloration transmitted to 

 the progeny ? In order to answer the first question, the experi- 

 ments were conducted in a methodical manner. 



Whoever carefully investigates large and the largest collec- 

 tions, cannot deny the fact that aberrations appear in years 

 with many strong temperature variations, or from localities in 

 which sharp changes are a common occurrence ; for example, in 

 certain mountain valleys, particularly in the Alps. 



Perhaps the true reason is to be found in the important and 

 lasting reduction of temperature caused by storms, especially 

 when accompanied in flat regions by hail, and in mountainous 

 regions by snow-storms ; at least this appears to be the con- 

 clusion to be drawn on the one side. 



Experiments were therefore made with 0° and —2° in various 

 ways, so that the most extreme variations of temperature which 

 could happen in such cases should be imitated ; but the result 

 of all these experiments was absolutely nil, in spite of the large 

 number of individuals dealt with. 



Only by the repeated application of —5° were a few aberra- 

 tions obtained. 



It is apparent that a repeated occurrence of — 5° during the 

 warmer portions of the year is out of the question. Still less a 

 repeated occurrence of —8°, -9°, -12° C, &c., under which 

 conditions experimental aberrations were constantly obtained, 

 although only few in number. Another fact which must be well 

 borne in mind, is that this result was only obtained with species 

 whose whole life-history from ovum to imago is achieved during 

 the warm portions of the year, and which hybernate as ima- 

 gines ; but this was not the case, at least as far as present 



