i6o 



Outline of Genetics 



of work has finally developed a desirable new strain of corn by 

 selection, he is not likely to favor hybridizing with some other 

 strain in any wholesale way. He must preserve his pure strain 

 at all costs. Shull has suggested the following solution of this 

 practical problem, as indicated in fig. 26. Two desirable strains 

 {A and B) are developed. One small plot (I) is planted entirely 

 with A, and at some distance another small plot (II) is planted 

 with A and B in alternating rows. Plot I is used only to perpetu- 

 ate A in pure condition. In plot II all the .1 plants are detasseled. 

 The silks of these .1 plants, therefore, are pollinated by B pollen 

 only, and the resulting grains in the .1 rows are all bound to be 

 hybrids. Using these grains as seed for the crop, hybrid vigor 



A B A B A B 



PLOT I PLOT 11 



Fig. 26. — Shull's scheme of planting for making practical use of 

 hybrid vigor in corn. 



will be obtained. At the same time both .4 and B are perpetuated 

 in the pure condition, since the B rows in plot II are always self- 

 pollinated, as there is no other pollen in that neighborhood. This 

 is a very simple solution of the problem, without necessitating 

 laborious hand pollination. 



The investigations and conclusions of East (5) may 

 next be considered. Shull did his work entirely with 

 corn, but East investigated the problem in a more whole- 

 sale way. After assembling an extensive collection of 

 data, he made the summarizing statement that 59 out of 

 85 angiosperm crosses showed a noticeable increase in 



