274 GENETICS IN RELATION TO AGRICULTURE 
produced 39 variegated ears and 36 pure white ears, which is clearly 
a 1:1 ratio in each case. This proves that both types of grains were 
heterozygous for a dominant mutant factor and that both of the factor 
mutations occurred in only one member of a duplex pair of factors. Pre- 
sumably the mutation from white to variegated occurred first, and later 
the mutation from variegated to red in a cell so located that, as the shoot 
developed, only a portion of the ear was affected. 
There appears a very important obstacle to the conception of ‘somatic 
segregation” in that the mechanism of cell division is apparently one of 
the most nearly perfect and regular of natural systems and that the order- 
liness of procedure is especially notable in undifferentiated tissue, where 
bud sports and chimeras commonly originate. To assume that the oc- 
currence of self-colored flowers on variegated plants is due to chromosome 
aberrations in mitotic divisions is much less plausible than to explain such 
phenomena by assuming a simple factor difference as responsible for self- 
color and variegation, and that changes from one state to the other are 
possible under certain conditions. This is the only reasonable hypothesis 
by which to explain mutations from the recessive to the dominant condi- 
tion of a pair of factors, as we have seen in the case of Hartley’s ear of red 
and variegated corn. ‘Therefore, while chromosome aberrations are 
known to occur during mitosis and aberrant numbers of chromosomes 
have been found in senile and diseased tissues, yet, in general, bud sports 
and chimeras are satisfactorily explained on the basis of factor mutations; 
whereas “‘somatic segregation’’ as the term has been used by Bateson, 
Gates and others implies the common occurrence of breaks in the 
mechanism of mitosis such as are not known to occur in normally 
functioning somatic cells. 
It should be remembered that horticultural literature contains nu- 
merous peculiar cases of discontinuous variation, many of which have been 
described or “explained” as “somatic segregations”’ resulting from 
hybridization. We believe that most of these cases can be explained 
much more reasonably in terms of factor mutations. But certain 
discontinuous variations in plants are undoubtedly the result of neither 
factor mutations nor chromosome aberrations in vegetative tissues. 
For example, persistent and deciduous calyx lobes are sometimes found 
on fruits of the same plant especially in the rose family. Tufts has 
described the occurrence of this phenomenon in the Le Conte pear and the 
Transcendant crab-apple as ‘‘somatic segregation,” assuming that some 
sort of segregation-mechanism exists in the division of somatic cells. 
Data from the pear tree gave a ratio of 3.15 deciduous to 0.85 persistent 
lobes. But to assume irregularities in chromosome behavior such as 
would cause segregation preceding the formation of nearly one-fourth of 
the calyx lobes on the tree is unwarranted in view of the general regularity 
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