l62 



Plant Genetics 



preserve his pure strain at all costs. Shull has sug- 

 gested the following solution of this practical problem, as 

 indicated in fig. 37. 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 perpetuate strain A in pure condition. In 

 plot II all the A plants are detasseled. The silks of 

 these A plants, therefore, are pollinated by B pollen only, 



A B A B A B 



PLOT 1 p^Q^ I, 



Fig. 37. — Shull's scheme of planting for making practical use of 

 hybrid vigor in corn. 



and the resulting grains in the A rows are all bound to be 

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

 vigor will be obtained. At the same time both A and B 

 are perpetuated in the pure condition, since the B rows 

 in plot II are always self-polHnated, 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 (2) may 

 next be considered. Shull did his work entirely with 

 corn, but East investigated the problem in a more 

 wholesale way. After assembling an extensive collec- 



