PLANT HYBRIDIZATION BEFORE MENDEL 



307 



actual ratios of 32:65:138, approximate almost exactly to the 

 theoretical ratio of 33:65:132. 



It therefore appears from the above analysis that there are, in 

 all, nine sorts of forms, as follows, and in the following propor- 

 tions : 

 AABB AAbb, aaBB aabb, 2AABb 2aaBb, 2AaBB, 2Aabb, 4AaBb 



This expression is evidently a combination series, representing 

 the product of the algebraic expression 



(AA4-2Aa+aa) X (BB+2Bb+bb), 

 and expresses the full number of possible combinations of germ 

 cells in the hybrids. 



After having determined the behavior of the offspring of hy- 

 brids in which two pairs of characters were involved, Mendel pro- 

 ceeded to investigate the behavior of hybrids where three charac- 

 ter-pairs are introduced, e.g. : 



1. Form of seeds, whether round or wrinkled, 



2. Color of seeds, whether yellow or green, 



3. Color of seed-coats, whether grey-brown or white. 



As Mendel says (p. 353), "among all the experiments it de- 

 manded the most time and trouble." 



From the 24 crosses made, 687 seeds were produced. From these, 

 in the succeeding year, he raised 639 plants which bore fruit. The 

 characters are indicated as before : 



Dominant Recessive 



A — round seeds a — wrinkled seeds 



B — yellow seeds b — green seeds 



C — grey-brown seed-coats c — white seed-coats 



The character of the seeds borne by these plants was as follows 



CLASS I 



Formula 



Appearance of the seeds 



round yellow grey 

 round yellow white 

 round green grey 

 round green white 

 wrinkled yellow grey 

 wrinkled yellow white 

 wrinkled green grey 

 wrinkled green white 



Average 10 



