No. 556] DEVELOPMENT IN NICOTIAN A 223 



ing sterile anthers with which Bateson 28 experimented. 

 While the number of plants has not been large in any of 

 these cases, one wonders why it is always the abnormal 

 (pure) class which is deficient. If the reduction phe- 

 nomena in the ovules of the abnormal Nicotiana agree 

 with the conditions present in the anthers, it seems not 

 unreasonable to believe that there may be a relation be- 

 tween the mortality of the gametes carrying the factor 

 for abnormalness and the deficiency in the ratio. In- 

 creased mortality of this class of gametes over the nor- 

 mal class would reduce the chances for combinations of 

 the abnormal gametes, and as a consequence the normal 

 and heterozygote combinations would be increased. 



Summary of Observations 



Concluding, one must bear in mind that the facts so 

 far obtained seem to warrant the belief that some agent 

 is at work on the internal structure as well as on the so- 

 called external, and is of such a nature as to produce ab- 

 normalities in cell structure as well as in cell complexes 

 or plant organs. The data, as a whole, raise a question 

 as to the significance of chromosomes in inheritance. 



Two strains of Nicotiana tabacum have been investi- 

 gated, one being a sport from the other. The sport has 

 been shown to differ from the normal in the possession 

 of a unit character due to one Mendelian factor. When 

 it is crossed with the normal, there results in F 2 a simple 

 Mendelian ratio of 3 : 1 as regards normal and abnormal 

 characters. The heterozygote is, with a little practise, 

 distinguishable, making the ratio 1:2:1 with abnormal- 

 ness partially dominant. The F 3 generation has proved 

 these segregates to breed true. Absolutely clean normal 

 segregates appear in F 2 and breed true. The abnormal 

 character has been described in detail, and shown to 

 affect practically all the structural parts of the plant 

 individual, even to the germ cells. Both strains have 

 the same chromosome number, 48 and 24, as a definite 

 mode. 



!8 Bateson, W, and others, Reports to the Evol. Com., II, p. 9], 1905. 



