SUGGESTIONS FOR RELIABLE HYPOTHESES 169 



(Peas, for instance, with different flowers or colour of 

 seed), new combinations can be formed according to 

 mathematical laws, which, when care is taken to ensure 

 self-fertilization, are constant. The experiments render 

 it probable that accidental qualities, such as size, 

 colour, length of life, and many others, are connected 

 with certain corporeal parts (Gens) and maintain 

 an independence in the organism. If, for instance, 

 there be crossed a dwarf race with a very large one, 

 it may happen that all the progeny may be large or 

 all dwarf, according to whether the ' gen ' of the c large ' 

 or that of the ' dwarf ' becomes utilized. 



Mutations and Mendelism both are adverse to the 

 smallest scarcely appreciable deviations. The greatest 

 hopes have been built upon Mendelism, which, however, 

 have mostly been unjustified. Crossing occurs certainly 

 in free nature generally only between individuals of 

 the same species. Most of the systematic species do 

 not admit of fruitful intercrossing. Lepus limidus 

 (the Hare) never crosses with the northern Lepus 

 variabilis ; the two species of Sparrows, house and field 

 sparrow, never cross ; horse and ass as a rule only by use 

 of artifice, etc. Just so there has hitherto been no cross 

 between apple and pear, despite their near relationship. 



With plants it is a general rule that self-fertiliza- 

 tion should be avoided (lowest limit), but, almost equally 

 so, crossing between species (highest limit). 1 Some 



1 ' The union of sexual cells follows, as a rule, only if they are derived 

 from individuals of the same species ' (Strasburger : Lehrbuch, p. 264). 

 ' Self-fertilization ' is mostly only an ' aid in need ' (same author). 



