THE CYTOPLASM 



The relationship between ambilinearity and suppressiveness is 

 further clarified by the inheritance of one of the many types of 

 variegation of the fern Scolopendriiun vulgare studied by Anderson- 

 Kotto. In this type of variegation the diploid sporophytes are pale 

 green with dark green sectors, which are produced by genetic change 

 early in development. There is some determinant which bleaches 

 or starves the clilorophyll in the plastids and this determinant is 

 unstable; or perhaps, by sorting out, it fails to get into every cell 

 of the rapidly growing young fern plant. Whole sporangia carrying 

 this determinant give purely pale haploid gametophytes. Other 

 whole sporangia give purely green gametophytes. Since there is 

 no segregation within sporangia where meiosis occurs, the deter- 

 minant cannot be nuclear. Now the green gametophytes breed true, 

 and when self-fertilized the pale gametophytes give variegated 

 sporophytes once more. It is thus only the pale determinant which 

 is unstable or is sorted out, and that is only in the young sporophyte. 

 When the pale and the green gametophytes are crossed, however, 

 the sporophytes are variegated and the result is the same both ways ; 

 thus the scheme is as in Table i8. 



TABLE 18 



INHERITANCE OF VARIEGATION IN SCOLOPEN DRI UM 



VULGARE 



2x variegated 



X green X pale 



reciprocally I 



I 1 



2x green variegated variegated 



The unstable determinant, being carried with equal effect by eggs 

 and spermatozoids, cannot be in the plastids. Nor, in the absence 

 of segregation after meiosis, can it be in the nucleus. It must be a 

 plasmagene, and one which is again both ambilinear and, in the 

 fertilized egg, suppressive. 



As a plasmagene the bleaching agent of Scolopendrium tells us two 

 new things, A plasmagene, like a nuclear gene, can control the 

 plastids. It can also be unstable, but its instability is no doubt due 



i86 



