46 



GEORGE HARRISON SHULL 



recognize in heterosis a potent source of practical gains, to be investigated, 

 understood, and utilized as a new tool in deriving from plant and animal 

 life their maximum contributions in the service of man. 



Although no further experimental work was done with corn at the Station 

 for Experimental Evolution after 1912, I tried to resume the work in my 

 first two years at Princeton University, by planting 77 cultures of pedigreed 



8 



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'^ /' %fi> X ^h QA >S^ 



A 



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3 /^ X B 



S 3. 



Fig. 2.9 — Ears of my white dent "strain" of corn grown at Princeton University in 1916. 

 The ears, each typical of the progeny to which it belonged, are from left to right : SA, Shull's 

 Strain A; SA X BA, Fi hybrid between Shull's Strain A and Biakeslee's "branch" of the 

 same strain; BA X SA, reciprocal of the last; BA, Shull's Strain A, after two successive 

 sellings by Dr. A. F. Blakeslee; B.\ X B, Fi between Biakeslee's branch of Strain A and 

 Shull's Strain B; and SB, Shull's Strain B. About as much heterosis is shown by a cross be- 

 tween two sub-hnes of Strain A as between one of these sub-lines and Strain B, the impli- 

 cation being that something more specific may be involved in this example of heterosis than 

 the mere number of genetic difTerences. (Photo by W. Ralph Singleton in 1945.) 



corn in 1916 and 65 in 1917. 1 used some of the materials from these cultures 

 for laboratory studies in biometry in my classes in genetics. The interesting 

 results shown in Figure 2.9 are from my 1916 crop at Princeton. The plantings 

 at Princeton were made late and the young plants were decimated by pigeons 

 and crows, so that some valuable connections were lost, and with them some 

 of my interest in their continuation. 



As we all know, heterosis is not limited to corn, and my own interest in 

 the matter was in no wise restricted to its manifestation in corn. There were 

 examples presented in many other of my genetical experiments. I was par- 

 ticularly interested in the discovery of such special mechanisms as balanced 

 lethal genes in the Oenotheras and self-sterility genes in Capsella grandiflora 



