2 26 POPULAR SCIENCE MONTHLY. 



munity which a few years ago was properly characterized as more 

 Darwinian than Darwin might now be described as more Mendelian 

 than Mendel, and expects to find in 'Mendel's laws' an explanation 

 of heredity, to say nothing of other things. Crosses between some 

 twenty-six close-bred varieties of plants and animals have been found 

 to 'Mendelize,' as the new expression is, and it may be expected that 

 others will do the same wherever the conditions of the experiment 

 can be met, though no amount of similar facts would justify the 

 general conclusions which some recent writers have so promptly drawn. 

 'Mendel's laws' have already had many different statements, but the 

 most that can be said with certainty is that after close-bred varieties 

 of a plant or animal have sufficiently separated, their divergent char- 

 acters do not again blend or reduce to an average, but draw apart into 

 definite proportions of each succeeding generation of ofllspring. Ob- 

 viously, this is not a method or law of inheritance, but of non-inherit- 

 ance or fractional inheritance. The sterile and aberrant hybrids are 

 evidence that too wide crossing is not advantageous and makes no 

 contribution to evolutionary progress. Mendel's experiments afford 

 further evidence of the same fact, in that the organisms themselves 

 are found to have means of dissolving such alliances and thus of 

 holding to the paths on which their varietal divergencies have gone 

 forward. The theory that hybridization assists evolution by encour- 

 aging variability is shown to have a distinct limit, since little evolu- 

 tionary progress would come from mere combination of the stable or 

 divergent characters which are a prerequisite of the Mendelian ex- 

 periments. 



Synthetic or Blended Hybrids. — If the normal flexibility of the 

 organism has not been diminished by narrow segregation or inbreed- 

 ing, the Mendelian repugnance of divergent characters does not ap- 

 pear; Mendel's law of reciprocal characters gives place to Spillman's 

 law of blended or graded characters.* Thus there is no record of a 

 normal straight-haired white child as the offspring of two mulattoes. 

 Inbreeding to an extent far beyond anything usual in nature is the 

 rule among domesticated plants and animals, but if the varieties are 

 not too divergent they cross freely and with obvious advantage, as 

 shown by increase in vigor, though such 'new characters' soon disap- 

 pear under renewed inbreeding. Characters which would become 

 dominant in the Mendelian hybrids are in the less divergent stages 

 termed prepotent, that is, they are impressed with increased intensity 

 upon increasing numbers of each successive generation. On the other 



such expressions as * Mendel's laws of the disjunction of characters in hybrids,' 

 or ' Mendel's laws of reciprocal hybrids.' 



* ' * * « hybrids show every possible gradation between the characters of 

 the two parents.' 



