544 THE POPULAR SCIENCE MONTHLY 



The Mendelian law is concerned with the dominance and recessive- 

 ness of plant and animal characters. It was clearly shown by Mendel, 

 and later by Correns and de Vries, that, given a single plant with a 

 character we wish to perpetuate, among a hundred of that individual's 

 grandchildren, there can be secured twenty-five that will be counter- 

 parts of their unusual grandparent, so far as the one special character 

 is concerned. This percentage is obtained by mating the prodigy with 

 ordinary stock and excluding the resultant hybrids from being fertilized 

 by any but other produce of the same original unusual individual. 

 Another twenty-five per cent, will be equally as capable of reproducing 

 the opposite character of the individual from which they sprang. The 

 remaining fifty per cent, appear true to the type of their hybrid parents, 

 but, like them, reveal their actual identity when their offspring follow 

 the same unusual proportions. 



The fact that such proportions can be relied upon added a new feel- 

 ing of certainty and greatly encouraged attempts to perpetuate and 

 multiply various features of plants. Of course, in the first generation, 

 the prized character of the parent may be recessive or prevented from 

 asserting itself by the more powerful opposite, and, until it was known 

 that one-fourth of the next generation might return to the character in 

 question, many attempts to breed in new features were abandoned after 

 the apparent failure of the first cross. Instances of the operation of the 

 same law were found in the animal kingdom. 



Castle found that in guinea-pigs the extra length of hair was dom- 

 inant over short hair which reappeared in Mendelian proportions in the 

 succeeding generation. Albinism and smoothness of coat were also 

 found to be inherited as recessive Mendelian characters. But of even 

 greater interest than these unusual proportions is the exhibition of 

 inheritance by unit characters. When we see length of hair being 

 inherited independently of its color, and each of these independent of 

 arrangement as to roughness or smoothness, we begin to realize the 

 vast number of unit characters that go to make up an organism. 



The unusual proportions, occurring so nearly accurately in large 

 numbers, were highly interesting to the biologists and very suggestive 

 to many persons not previously interested either in botany or zoology. 



Mendel's law was of the greatest importance in pure science be- 

 cause any explanation of the fixed proportions must be based upon the 

 nature of the gametes, and much new theory and research was under- 

 taken to ascertain the basis of such seeming unnatural exactness of 

 proportion. 



If we assume that the gametes produced by hybrid individuals are 

 pure to one or the other of the parental characters, the explanation of 

 the Mendelian proportions is comparatively simple. Such assumption, 

 however, is not justifiable in the light of our present knowledge. A 



