38 Genetic Studies hi Potatoes; Steriliti/ 



of segregation has occurred at which the basis of sterihty has dropped 

 out of the hneage of the tuale germ cells. On the other hand the germ 

 lineage of the eggs is unaffected so that male sterility is present in some 

 of the egg cells and is absent from others ; this may well be merely the 

 result of normal segregation. Possibly in the developing bud at the time 

 when the male organs of the flower are being differentiated a differentia- 

 tion of genetic characters takes place. This hypothesis affords an ex- 

 planation of the rather paradoxical male fertility of Edzell Blue in spite 

 of its containing the dominant element of male sterility. For as a result 

 of the premature segregation the primordia of the antliers would only 

 contain the basis of fertility and are therefore able to form good pollen. 

 It would account for the fertility of t\ and F2 from the cross Edgecote 

 Purple X Edzell Blue and for the fertihty of the reciprocal crosses be- 

 tween Edgecote Purple x Myatt's Ashleaf. The F-^ result from the cross 

 Edzell Blue x Myatt's Ashleaf which was similar to that of Edzell Blue 

 X Edgecote Purple is also intelhgible on the above hypothesis. A diffi- 

 culty is met however in the result from Edzell IMue selfed. According to 

 the theory about half the eggs carry sterility and the other half fertility 

 while all the pollen carries fertihty. Consequently selfing should give 

 half sterile and half fertile offspring, i.e. the same result as Edzell Blue 

 < Edgecote Purple. But the data (Table I) indicate an excess of fertiles. 

 The numbers are small but the discrepancy demands further investiga- 

 tion. Again, no explanation is afforded of the rather imperfect pollen 

 production of Edzell I51ue. 



To sum up it appears that in male sterile varieties the eggs either all 

 carry male sterility or some carry male sterility and the remainder male 

 fertility. The eggs of male fertile varieties (except Edzell Blue) and the 

 pollen of all male fertile varieties tested carry male fertility. As sterility 

 behaves as a dominant the F^ from a cross, sterile x fertile, consists of 

 all steriles or partly of .sterile and partly of fertile plants. 



Miss Saunders (4) in her classical experiments with Matthiula has 

 shown that the pollen of certain "singles" is all of one kind, but that the 

 eggs are of two different kinds with respect to the "doubling" factors. 

 Other experiments (5) suggest that in Petunia the pollen is heterogeneous 

 and the ovules homogeneous for a "singleness" factor. The present data 

 point to an explanation of the former kind in potatoes. 



If we regard a male-sterile plant as a functional female it follows 

 that the gametes of Edzell Blue are differentiated in regard to sex, the 

 eggs carrying either Hermaphroditism (cj Fertility) or Femaleness (o 

 Sterility) and the sperms all Hermaphroditism (cJ Fertility). 



