276 POPULAR SCIENCE MONTHLY. 



in related varieties, where the remaining characters of both varieties 

 are unimportant. Hence, in practice, we have in reality to deal with 

 dihybrids in many cases. It should also be remembered that, if we 

 treat a hybrid as a dihybrid, neglecting all but the two characters of 

 most concern, the type we select actually splits up into fixed types 

 with reference to all other characters, so that in a few generations we 

 can secure uniformity, even in minor characters, by selection. 



There is a very interesting phase of the subject which, for the sake 

 of clearness, has been purposely overlooked in what has been said above. 

 We have dealt only with the case in which a parent character appears 

 in the hybrid in a fully developed state, or is not apparent at all. This 

 is actually the case with the characters discussed above. Cases are 

 known, however, in which both of a pair of opposite characters appear 

 in the hybrid. This may result in a form intermediate between the 

 parents, as I found to be the case when I crossed short-headed club 

 wheats with the ordinary long-headed varieties. The same phe- 

 nomenon appeared in crosses between varieties with red chaff and 

 those with white chaff. Sometimes, in crosses between white and red 

 flowers, for instance, the heterozygote types are variegated. It is 

 easy to see that this fact may have an important bearing on the 

 flavor and other characters of hybrid fruits, such as apples, peaches, 

 strawberries, etc. It is highly probable that a great majority of these 

 fruits are heterozygote in character, which fact would explain their 

 well-known variability when grown from seed. It would naturally be 

 expected, since flavors are due to the presence, in various proportions, 

 of certain chemical substances, that entirely new flavors should be 

 found in seedlings of this character, for in almost every seedling we 

 should have a new combination of the flavor-giving substances. 



One reason why Mendel's law was not discovered long ago is doubt- 

 less to be found in the fact that the large majority of seedlings that 

 have come under the breeder's eye have had heterozygote parents of 

 unknown constitution. If all our leading commercial varieties had 

 been commonly close-fertilized, the law would long ago have forced 

 itself upon us. Professor Bailey's remarkable and careful work on 

 hybrid squashes and pumpkins probably came to naught for this very 

 reason. Had he done the same work with varieties that are normally 

 close-fertilized, he would probably have discovered this law. He was 

 on the right road, but he was in the wrong vehicle. 



Let us consider what results would follow the growing of apple 

 seed generation after generation with close-fertilization, if the char- 

 acters of the apple obey Mendel's law. We start with a tree that is 

 already multihybrid. Suppose it to consist of N pairs of opposite 

 character, A-A', B-B', : s N-N'. The hybrid and the first genera- 



