312 A TEXTBOOK OF BOTANY [On. VI, 8 



four modes of fertilization are possible ; a black from a male 

 nucleus may unite with a black from a female, or a black from 

 a male with a white from a female, or a white from a male 

 with a black from a female, or a white from a male with a 

 white from a female. Thus we can have four kinds and 

 only four, of fertilized egg cells, one containing two black 

 determiners, one containing two^jshite determiners, . and 

 two containing a black and a white. In other words, the- 

 oretically 1 of all the offspring of this couple will have the 

 black character only, the white being eliminated entirely from 

 their bodies and those of all their offspring if they breed only 

 with their own kind ; \ likewise will have the white character 

 only, the black being eliminated out of them and their off- 

 spring if they breed with their own kind ; and two J's, that 

 is J, of the whole will have the black and white both in their 

 own bodies, and can transmit either to their descendants, 

 although, as black is dominant to white, they will themselves 

 show only the black character, the white being latent or re- 

 cessive. Thus of all the offspring f will show the dominant 

 black and J the recessive white, though of the -f , f have the 

 white latent. The arrangement is represented for a single 

 character in Fig. 220. This fact was discovered by Men- 

 del in hybrids, but of course is equally true in principle for 

 ordinary offspring from parents of the same variety. It has 

 been found to hold true very widely, even though not uni- 

 versally, in a great many kinds of plants and animals ; and 

 it is the central feature of MENDEL'S LAW, now one of the most 

 prominent matters in all Biology. 



For the sake of the study of the principle we have re- 

 duced our subject to the utmost degree of theoretical sim- 

 plicity. In fact, however, matters are never so simple, and 

 commonly are vastly complex, in actual life. Thus, the 

 law only holds true as an average of high numbers, its oper- 

 ation being often obscured by chance with small numbers; 

 characters and determiners are not few in number, but 

 many, even to hundreds and thousands ; similar forms are 



