i88 MENDELISM 



was impossible to rank the individuals into definite 

 classes in respect of so indefinite a character as time 

 of flowering. On making a perfectly arbitrary division, 

 however, it was found that 175 purple and 104 white 

 plants were in flower on a certain day, and that 208 

 purple and 19 white plants did not open their buds 

 until afterwards. There is, therefore, clearly some 

 coupling between the presence of white blossoms and 

 early flowering on the one hand, and between lateness 

 and purple' flowers on the other. Two characters 

 more diverse than colour of the flowers and time of 

 flowering could at first sight scarcely be imagined. 



The second class of complications that we have to 

 deal with although the term complication may be 

 to a certain extent justified in connection with it 

 does not involve any exception to Mendel's law of 

 segregation. The phenomenon of so-called reversion 

 on crossing has long been familiar to biologists. Its 

 meaning, however, was totally obscure, and even the 

 Mendelian was at first unable to offer any explanation. 

 The phenomenon consists in the appearance, in the 

 offspring of a cross, of a character which was not 

 visibly present in either parent, and in many cases this 

 character can properly be regarded as ancestral it is 

 a character which has been lost by both parents in 

 the course of their divergent evolution from a common 

 primitive form. Now, these cases differ entirely from 

 those of the appearance of a heterozygote form on 

 crossing, such as are due to the combined action of the 

 two parental allelomorphs in the cross-bred offspring, 



