xiv] SOMATIC SEGREGATION 219 



at stages other than the maturation of the germ-cells is 

 provided chiefly by plants. "Bud-variation" is a not un- 

 common phenomenon in many plants, and the character 

 which distinguishes the varying shoot from the rest of the 

 plant may be one that is known to follow Mendel's law when 

 the two forms are crossed together. In such a case it is clear 

 that segregation has taken place between the main plant 

 and the varying bud. This, however, does not invalidate the 

 chromosome hypothesis, for the variation of the bud may 

 have been due to an irregular division in the cell from which 

 the bud was derived, by which, perhaps, one chromosome, 

 or part of a chromosome, was omitted from the daughter- 

 cell that gave rise to the bud. Less easy to explain are 

 those cases in which one part of a plant constantly bears 

 Mendelian characters that are lacking in another. In those 

 forms of the Stock (Mattbiola), for example, which are 

 heterozygous for the factor for doubleness, Miss SAUNDERS 

 has shown that all the pollen grains bear the recessive 

 double character, while of the ovules some bear the double 

 and some the single factor. In this form, therefore, the 

 dominant factor for singleness is eliminated at some stage 

 of the development of the pollen before the maturation 

 divisions take place. Another remarkable case is that de- 

 scribed by BATESON and Miss PELLEW in peas. Certain 

 peas throw a small proportion of abnormal offspring known 

 as "rogues," and when these rogues are crossed with the type 

 the young plants have the type form, but as they grow up 

 they become rogues and produce only rogue offspring. As 

 the heterozygous plant grows, the type characters (to quote 

 BATESON and PELLEW) "are in some way used up and cut 

 out of the germ-lineage in the early stages of the somatic 

 development." If the chromosome hypothesis be true, a 

 chromosome, or part of one, must apparently be omitted from 



