Studies of Teratological Phenomena. 119 



of each apparent class will differ but very little from each other, and 

 tliis slight difference may be described as the difference in external 

 environment. On the other hand, when two homozygous pure Hnes^) 

 differing in numerous factors are crossed, F2 individuals of each apparent 

 class may express the character especialh^ under observation in many 

 distinct morphological forms, each of these changes in expression being 

 the result of modification by other factor developments. Calycanthemy 

 (B) is not so easily altered in its expression by changes in factorial 

 complexes as is factor A. 



6. Summary and conclusions. 



The following conclusions may be drawn from this study: 



1. According to the evidence already presented, the original plant 

 which became the progenitor of this fasciated race, must have mutated 

 from unknown causes, at or shortly after fertiTization had taken place 

 (somatic mutation in the embryo). For the reasons given in the body 

 of this paper, the mutant is believed to have arisen in a homozygous 

 condition as regards the factor A and upon self-fertilization to have 

 bred true. 



2. The Cuban variety of tobacco known as 402 in the B. I. of 

 H. U. cultures is believed to differ from the Nicotiana tabacum fasciata 

 race (300 — 309) only in the absence or presence of a single genetic 

 factor (A). In all other respects, the twio races in breeding tests 

 give results that would lead one to believe them to be identical 

 genotypes. 



3. As a generality, N. tahacum varieties and races are held to 

 be natural pure lines (as reported by Hasselbring) and to give uniform 

 progeny in breeding tests of self-fertilized seed parents. Owing to 

 cleistogamy and the consequent rarity of cross -fertilization, such pure 

 lines, in the majority of cases, have bred true for thousands of 

 generations. The sexually produced progeny of these N. tabacum 

 homozygous pure lines, would differ in no way from the progeny that 

 might be created by asexual methods such as cuttings. 



^) In all the crosses of the fasciated race with normal varieties and species of 

 Nicotiana, all the Fj generation plants of a given cross were practically uniform in 

 appearance (height, flower-shape, and color, foliage and stem characters, etc.). This 

 fact indicates these normal parents to have been practically homozygous genotypes. 

 (See Tables.) 



