190 MULTIPLE FACTORS 



productivity depend on multiple factors. For ex- 

 ample, East crossed the strain Tom Thumb (having 

 short ears) to black Mexican sweet (having long ears) . 

 The relative length of ear in these two races is shown 

 in the upper line of Fig. 59, to the left and to the 

 right. A sample of the Fi ears is shown in Fig 59, 

 the middle of the figure, while the variability of the 

 F2 ears is shown in the lowest Hne. It is evident not 

 only that the original types reappear, but that there 

 are all intermediate lengths of ear in F2. 



Many cases like this one that show a small varia- 

 bility in Fi and a greater variability in F2 have been 

 described, for example, in oats (Nilsson-Ehle) , beets 

 (Kajanus), turnips (Kajanus), barley (Johannsen), 

 gourd (Emerson), flax (Tammes), tobacco (Hayes 

 and East), evening primrose (Heribert-Nilsson) , 

 bean (Emerson, Johannsen), pea (Tschermak), Lyon 

 bean (Belhng), w^heat (Nilsson-Ehle), corn (East, 

 Emerson, Hayes), duck (PhiUips), fowl (Pearl), 

 man (Davenport), rabbit (Castle, MacDowell), mouse 

 (Cuenot), rat (Castle, Hagedoorn).^ 



This partial list will serve to show how^ often this 

 form of inheritance has been met with, and when it is 

 stated that in a number of these plants or animals 

 several characteristics show this kind of inheritance, 

 its frequency will be apparent. Many but not all 

 of these cases relate to size, and size is obviously a 

 character toward which many separate parts con- 

 tribute. Moreover size is often an important element 

 in domesticated animals and plants, and any differ- 



1 This list is an abbreviation of the one compiled by G. H. ShuU. 



