11 



cross between ' Ne plus ultra' and ' White 

 flageolet ' it is seen that one of the white 

 derivatives from this cross has the same 

 gametic composition as the ' Marrowfat.' 



Emerson attempted no explanation of the 

 different behavior of these beans, simply pre- 

 senting them as exceptions to Mendel's laws 

 or as evidences of the limitation of the use- 

 fulness of those laws in predicting the results 

 of hybridization. Practically all of the ex- 

 ceptional results obtained by him cease to be 

 exceptional when we cease to look upon the 

 products of his crosses as monohybrids with 

 respect to seed color. His second generation 

 hybrids were classifiable into four categories 

 instead of the three he expected, but his ex- 

 pectation was based upon the assumption that 

 the black, brown, white, etc., are unit char- 

 acters, and that the mottled hybrids were 

 simply mosaics or blends between the white 

 and the self-colored parents. The simple as- 

 sumption, demonstrated in my hybrids, that 

 the pigmentation and the mottling are distinct 

 unit characters, harmonizes his results per- 

 fectly, though the numbers with which he 

 dealt were too small for the satisfactory de- 

 termination of the agreement or disagreement 

 with the theoretical ratios of a dihybrid. 



In discussing the appearance of purple 

 spotting as a novelty in peas, Lock 12 follows 

 Tschermak in referring the latent character to 

 the pigmented parent, saying that " On cross- 

 ing A(B} (B being latent) with ab we get: 

 F! ABab (B latent having become B active)." 

 If instead he had considered that Ab is 

 crossed with a,B, the A producing the pigment 

 and the B aggregating it into spots, he would 

 get the same F lf namely ABab, but would 

 have avoided the difficulty of a capricious unit 

 which may be active or inactive under condi- 



M Lock, R. H., ' Studies in Plant Breeding in the 

 Tropics/ Ann. Roy. Bot. Gard. Perideniya, 2: 

 299-356. See p. 341. 



