Lecture XXIX. 263 



found to be of two kinds, viz. round and angular. When a large 

 crop of these was harvested it was found that always approximately 

 25 per cent, of the crop was composed of angular embryos and 

 75 per cent, of round embryos. That is, in the F 2 generation three- 

 quarters of the total number of embryos exhibit the dominant 

 character and one-quarter exhibits the recessive one. When the 

 plants from all the seeds of the F 2 generation mature and are selfed, 

 an interesting difference is- found among those developed from the 

 rounded embryos, one-third of these produce rounded embryos 

 only, while in the pods of two-thirds both round and angular 

 embryos are found. In these pods the proportion is 3 round to 

 i angular. In the pods of the selfed plants derived from the 

 angular embryos no round embryos are to be found. 



The experiment may be summarised by the following diagram, 

 where the plants derived from the round seeds are represented as 

 circles and those derived from the angular seeds are represented 





FIG. 93. Diagram to illustrate the transmission of roundness and angularity 

 in three generations. The small enclosed figures indicate the determin- 

 ants in the germ-cells. 



by quadrate outlines. In point of fact in the embryonic state 

 the plants are round and angular respectively. 



It should be particularly noticed that individuals may be found 

 in the first generation after a hybrid (F 2 ) which breed true respect- 

 ing either allelomorph. Thus in the F 2 some of the round 

 individuals on being selfed will produce only round offspring, and 

 similarly all the angular on being selfed produce only angular 

 offspring. It follows that, with regard to the differentiating 

 characters of a hybrid union, 50 per cent, of the offspring are pure. 

 Of this 50 per cent., half transmit one allelomorph and half 

 transmit the other. 



These observations Mendel explained as follows : The original 

 two lots of tested seeds grew into plants which produced gametes 

 containing in their germ-plasm determinants (factors) of roundness 

 and angularity respectively. When crossed an oosperm was formed 

 in which determinants of roundness and angularity were contributed 



