ix] and Spurious A ' llelonwrphism 157 



bination of hooded standard with round pollen must be 

 exceedingly rare in any of these families. If the gametic 

 coupling is 



7 Blue long + i Blue round + i Red long + 7 Red round, 



the zygotic expectation is, in the simpler case where all the 

 standards are erect, 



177 Blue long + 1 5 Blue round + 1 5 Red long + 49 Red round. 



But when the standards may be either erect or hooded, 

 all the hooded plants are homozygous in B, and the expecta- 

 tion of a round-pollened plant occurring among the BB class 

 is only i in 64. Observation agreed with this expectation, 

 for in the F z families which certainly all followed the 7 : i 

 system, there were 83 hooded purple plants and of them 

 one was round-pollened. The same expectation holds in 

 regard to the hooded plants with white flowers, which also 

 must all be BB. Unfortunately most of these were recorded 

 before the importance of the question was appreciated, 

 and in them the hoods were not noted. Of 17 plants 

 of this class which were examined 16 were long and 

 i was round. 



Similarly, when the coupling is on the 15 : i : i : 15 

 system the hooded purples will be still rarer, and should 

 occur only as i in 256 of their class. Among the 9 

 families which definitely followed the 15 : i plan, one 

 hooded round occurred among 209 plants of the hooded 

 class. 



Discussion of the Physiological Significance of Gametic 

 Coupling and Spurious Allelomorphism. 



The significance of the phenomena just described lies in 

 the fact that they demonstrate the existence of a complex 

 interrelation between the factorial units. This interrelation 

 is such that certain combinations between factors may be 

 more frequent than others. The circumstances in which 

 this interrelation is developed and takes effect we cannot 

 as yet distinguish ; still less can we offer with confidence 

 any positive conception as to the mode in which it is 

 exerted. 



