Nov.. Hil(>] Cytoplasm and Heredity 3 



Flowers borne upon green branches, if self-fertilized, give 

 seed that produces only green offspring. Flowers upon white 

 branches if self-fertilized, give seed that produces only white 

 offspring, which soon die because unable to carry on photo- 

 synthesis. Flowers on variegated branches yield offspring some 

 of which are white, some green, some variegated. 



Crosses between flowers upon green branches and flowers 

 upon white branches yield the important result that only the 

 mother determines the chlorophyll character of the next gen- 

 eration. Correns found that when, in such crosses, the flower 

 used as a female was on a green branch, the offspring were all 

 green. If the flower used as a female was on a white branch, 

 the offspring were all white. A flower on a variegated branch 

 yielded seeds that produced variegated plants, regardless of 

 whether the pollen came from a green, a white, or a variegated 

 branch. As regards this color character, the offspring are 

 always like the mother. Even in subsequent generations, there 

 is no reappearance of the paternal character. Domination by 

 the female is even more rigid in these garden plants than in 

 human families. 



What causes this peculiar course of heredity may be ques- 

 tionable; but Correns suggests that it is due to a disease 

 transmitted only through the cytoplasm of the egg. No gen- 

 eralization can be made in regard to variegation, for in other 

 plants this character is found to be inherited through the sperm 

 also; but there appears to be no doubt that in Mirabilis it is a 

 cytoplasmic character. 



Similar evidence of cytoplasmic influence in heredity is to 

 be found in what are called matrocline hybrids. When two 

 crosses are made between two races or varieties, the mother 

 coming from race A in one case, from race B in the other, these 

 crosses are called reciprocal crosses; and the first generation 

 hybrids from these crosses are known as reciprocal hybrids. In 

 ordinary Mendelian cases, the two reciprocal hybrids are 

 theoretically equal. If the chromosomes are the bearers of 

 hereditary factors, and if there is no disturbance in the normal 

 chromosome behavior, the reciprocal hybrids should be equal. 

 But in certain cases they are not equal, each reciprocal being 

 more like the mother which produced it. Unequal reciprocal 

 hybrids which resemble the mother more than the father are 

 described as matrocline hybrids. 



