QUEEN-REARING IN ENGLAND. 55 



shape of seed — whether rounded or wrinkled, position of 

 flowers — whetlier distributed along the stem or terminal, 

 shape of ripe pod — whether inflated or constricted, and 

 colour of seed skin — brown or white, cotyledons — yellow or 

 green, and unripe pod — green or yellow. 



The phenomenon of dominance, remarkable as it is, is 

 not the essential part of Mendel'-s discovery, indeed, it is 

 not present in every case, the first generation of the hybrids 

 being sometimes intermediate in character. We must bear 

 in mind that an individual animal or plant is the product of 

 the union of two germ cells, or gametes, as they are called, 

 the one derived from the male parent, and the other from 

 the female parent. Thus an, individual is of double origin. 

 Now the essential part of Mendel's discovery, recognised 

 by the discoverer himself, is that the gametes are pure in 

 respect of either of the characters in each of the pairs of 

 alternative characters we have been considering ; in other 

 words, that a gamete can carry one of the characters of a 

 pair, but not both. 



In Mendelian, language the individual animal or plant 

 is called a zygote. If the two gametes that go to make a 

 zygote carry the same character, the zygote is called a homo- 

 zygote. If they carry opposite characters it is called a 

 heterozygote. 



By applying this theory to the results obtained by cros- 

 sing the tall and dwarf peas, we see how perfectly it accounts 

 for them. The individuals of the first generation contain 

 and produce gametes bearing the elements representing tall- 

 ness and shortness_ in equal numbers, and the results we get 

 in the second generation are simply due to the segregation 

 of these elements. As Bateson has remarked, the most 

 striking consequence of Mendelian inheritance is the para- 

 dox that pure individuals may be bred from impure ones. 

 Once the opposite character has been eliminated the indi- 

 viduals remain pure for any number of generations. Recent 

 investigation suggests that the dominant may owe its domin- 

 ance to a factor which is absent in the recessive; therefore 

 we are not concerned with two opposing factors, but the 

 presence or absence, of a single factor. When the hetero- 

 zygote is intermediate, we have no means of knowing in 

 which of the two pure kinds of individuals the factor resides. 



