82 White. 



F. Special study of fasciation in Nicotiaua. 



1. Problems. 



Chief among the problems involved in this particular study, is the 

 effect of diverse and unrelated genetic factors in their ontogenetic 

 expression upon that of the fasciation factor. Owing to the historical 

 data extant concerning the origin of this fasciated race, one is almost 

 justified in saying that in this particular case, through comparison with 

 its normal parent, and through crossing, an isolation of a factor has 

 been accomplished. If to some, this statement is not justified by the 

 data which is to follow, I feel that at least, I have found ideal material 

 to serve as a standard with which to compare the variation in expression 

 which takes place when this race is crossed with other races, and thus 

 better appreciate the true nature of the phenomena of dominance. Other 

 problems more or less associated with this main problem are : the nature 

 and causes of dominance, the ability of selection to modify a unit factor, 

 the relation between fasciation and environment, the nature of Mendelian 

 segregation when two abnormal hereditary characters are combined 

 through crossing, the appearance of mutations in controlled cultures, 

 and the fidelity with which pure homozygous Fa segregates breed true 

 in later generations. 



It is realized, however, that the data secured on the problems of 

 selection and the modification of unit factors, are too few to be of 

 more than suggestive value. 



2. Materials and methods. 



The material upon which the study is largely based is a fasciated 

 race of Nicotiana tahacum. In connection with the hybridization 

 experiments, cultivated and wild species and varieties of Nicotiana, 

 which have been tested in controlled cultures for at least two years 

 were used. These types were obtained by Dr. East from Prof. W. L. 

 Setchell, from Mr. J. S. Dewey, from Prof. A. Splendore and Prof. 

 0. Comes through the kind offices of Mr. D. Fair child. To all of 

 these gentlemen the writer wishes to express his grateful thanks. 

 Nicotiana is an excellent genu§ on which to conduct investigations, and 

 of the numerous species it contains, Nicotiana tahacum is one of the 

 most favorable from a genetic standpoint, because of its large number 

 of distinct subspecies and varieties, the majority of which are practically 



