78 White. 



4. Very numerous, diverse internal and external factors operate 

 singly or in combination to develop fasciation. If these factors are 

 largely internal, and the race is naturally cleistogamous, the character 

 is generally hereditary and constant. If the factors are largely external 

 (insect depredation, mutilation, etc.) the character fasciation is neither 

 hereditary nor constant. If the fasciated race, to begin with, is not 

 genotj^ically homozygous, as is not the case when the individuals of a 

 species are naturally cross-fertilized, the character fasciation may be 

 hereditary, but present in only part of the progeny, owing to the 

 segregation of the primary internal factors for fasciation or to the 

 segregation of numerous other internal factors which may modify in 

 some manner the expression of those factors especially concerned in the 

 production of fasciation. 



E. Review of previous Meiideliau studies. 



1. Pisum sativum umbellatum Mill, is the only race of fasciated 

 plants which has been fully tested as to the discontinuous nature of its 

 inheritance in crosses with the normal race (Fig. 8). The fasciated character 

 of this plant was one of the original seven Mendelian character -pairs. 

 Mendel (Bateson 1909) found that crosses of fasciated X normal in 

 Fl gave complete dominance of the normal condition. In F2 the ratio 

 of abnormal to normal w^as 3* 14 : 1, Bateson and Punnett (Bateson, 

 1909, p. 25) repeated tliis experiment, but secured intermediates in F2. 

 Fasciated (terminal inflorescences) . . . 207 

 Normal (axial „ ) ... 651 



Total 858 

 Mendel's experiment was again repeated by Lock and later by 

 Darbishire. Lock hesitatingly confirms Mendel's results. The hesitancy 

 is caused by the variation in the fasciated character. Normal X fas- 

 ciated in F2 gave Lock (1908) approximately a 3 : 1 ratio, but many 

 of the fasciated F2 segregates expressed their anomalous character in 

 a much slighter degree than the fasciated grandparent ("Irish Mummy"). 

 Some of this modification in expression was ascribed to crowding and 

 to other unfavorable growth conditions, since the fasciated F2 segregates 

 "had to compete with thrice their number of normal sister plants, but 

 it did not seem likely that this would account for the whole difference". 

 'Seeds of very slightly fasciated plants were sown and the resulting Fa's 



