160 GENETICS IN RELATION TO AGRICULTURE 



ears with white cobs and variegated grains and ears with red cobs and 

 white grains. None were produced which bore ears having the Fi 

 combination, red cob and variegated grains, and on the other hand 

 none were produced showing the reverse recombination, white eafs and 

 white grains. 



This series of multiple allelomorphs is perhaps the most striking one 

 known and displays just as unique relations as does that series in Parat- 

 tetix. For considering only red vs. white alone in these characters 

 there are sixteen possible combinations which would give pure breeding 

 races. Besides this, however, the red, particularly of the pericarp, 

 may be modified in many different ways with respect to shade and 

 distribution, apparently without altering the relations of the factors 

 involved to the allelomorphic system, so that the number of possible 

 combinations is considerably greater. Emerson has studied the in- 

 heritance of a large number of these types and so far they all may be 

 consistently explained on the hypothesis of multiple allelomorphs but 

 the data are not as yet extensive enough to establish this interpretation 

 beyond any doubt. 



The general nature of multiple allelomorphism is attested to by its 

 occurrence in widely separated species of animals and plants. Its 

 occurrence in Drosophila, the silkworm, Parattetix, and maize has been 

 noted above. . Besides these Morgan has pointed out that cases are 

 known in rabbits and mice among animals, and in Aquilegia, Lychnis, 

 and the bean among plants. In rabbits the factors concerned are three, 

 those for self-color, Himalayan pattern, and albinism. In the mouse 

 apparently four factors make up a similar system, namely those for 

 yellow, black, gray, and gray with white belly. In Aquilegia the system 

 has to do with leaf color and three factors are involved, those for green, 

 variegated, and yellow leaf color. ShulPs case in Lychnis has to do 

 with sex-determining factors. In the bean the case is somewhat like 

 that in corn but the series is less extensive. The system there as re- 

 ported by Emerson is green leaves, green pods; green leaves, yellow 

 pods; yellow leaves, yellow pods. 



Morgan has brought together the arguments in favor of multiple 

 allelomorphism and the following discussion is based for the most part 

 upon his presentation. This discussion will serve in a sense as a summary 

 of the material dealing with multiple allelomorphism. 



1. Systems of multiple allelomorphs appear always to affect the same 

 character. This fact is readily apparent from a consideration of the cases 

 which have been cited above. Beyond this the cases often give a series 

 of diminishing intensities with respect to the character affected as for 

 example, black, Himalayan, and white in rabbits. On this basis, Pun- 

 nett has sought to disprove the validity of the hypothesis of multiple 



