490 University of California Publications in Botany [Vol. 5 



Stenophylla X angusti folia. Reciprocal crosses were made between 

 F-, STENOPHYLLA of type 21 and angustifolia; H-6=^F5 type 21$ x 

 angustifoUa(^ and Hj-, its reciprocal. Stenophylla of type 21 has been 

 described previously as a stable derivative closely approximating 

 angiistifoUa in all its characters. F^^ families of 50 plants of each 

 hybrid were raised in 1915. They were uniform throughout and so 

 close to angustifolia in all characters as to be indistinguishable from 

 it. One plant seemed to be of a slightly darker pink corolla color. 

 ISFsHjeaPii was the only ¥<, family raised. The flower color of this 

 population was about the shade of angustifolia and uniform through- 

 out the population. The family showed only a slight variation in the 

 base of the blade such as is also seen in populations of angustifolia. 



8. DISCUSSION OF EESULTS OF THE AXGUSTIFOLIA-MACROPHYLLA 



SERIES OF INVESTIGATIONS 



Obviously the outstanding result of this series of investigations of 

 hybrids between angustifolia and niacrophylldi is a demonstration of 

 the complexity of the germinal differences which exist between the 

 two varieties with respect to practically every character contrast which 

 may be made between them. Only in one instance, the contrast be- 

 tween the light pink flower color of angustifolia and the red of macro- 

 phylla, is a simple Mendelian formulation possible. Here evidently 

 the main flower color difference is dependent upon a simple allelo- 

 morphic contrast. Red x light pink gives F^ intermediate pink, and Fo 

 1 red : 2 intermediate pink : 1 light pink. The red segregants breed 

 true for red, the light pinks for light pink, and pink continues to 

 segregate in the typical mono-hybrid fashion. Inasmuch as the inter- 

 mediate pinks and light pinks form an intergrading series, it is con- 

 venient to look upon red as the recessive color. Accordingly we give 

 this pair of factors the designation, Rr, following the mnemonic system 

 advocated by Morgan, and shall so refer to it in what follows. The 

 difficulty among the pinks appears to be due not only to phenotypie 

 variation but also to the existence of modifying factors which have a 

 relatively slight effect upon flower color expression. These less strik- 

 ing modifications of flower color we are seeking to analyze further. 



In the leaf shape investigations, the complexity of the results is 

 plainly evident from an examination of the data presented in the fore- 

 going pages. Although the behavior here is complex, in every feature 

 it parallels the Mendelian expectation for complex factor relations. 



