362 GENETICS IN RELATION TO AGRICULTURE 



with a series of trials with varieties in alternate rows. After determining 

 which varieties are best adapted to the local conditions and give the best 

 results when crossed he will be ready to adopt a simple system of hybrid 

 seed production somewhat like the following. These directions have been 

 sent out by the United States Department of Agriculture to cooperative 

 experimenters. Various other plans could be devised. 



Experiments as outlined below involve the use of two varieties and two separate 

 plots. Varieties may be designated as No. 1 and No. 2, the plots as A and B. The 

 plots should be sufficiently separated to prevent cross-pollination between them. 



It should be kept in mind that the increased yield can be expected only for the one 

 year immediately following that in which the cross is made. 



Plot A is planted with alternate rows of No. 1 and No. 2. The rows planted with 

 No. 2 are to have all plants detasseled. The crop of No. 1 and No. 2 is to be saved 

 separately. 



Plot B is planted entirely with variety No. 2 and has alternate rows detasseled. 

 The crop from the tasseled and detasseltd rows is to be saved separately. 



At harvesting there will be the following lots of seed: 



1. Plot A. Variety No. 1, field-pollinated. 



2. Plot A. Hybrid between No. 1 and No. 2. 



3. Plot B. Variety No. 2, field-pollinated. 



4. Plot B. Variety No. 2, cross-pollinated. 



The yields in the year the cross is made should show the comparative value of the 

 two varieties and the effect, if any, of detasseling on the immediate yield. 



A comparison of the yield from these four lots of seed the following year should 

 show the yield of the first-generation hybrid as compared with the pure varieties and to 

 what extent the increase, if any, is due to the elimination of self-pollinated seed. 



If plot B cannot be provided, seed of variety No. 2 should be held for planting the 

 following year in comparison with variety No. 1 and the hybrid seed. 



Application in Other Annual Crop Plants. The increased vigor due 

 to heterozygosis has not yet been utilized in a practical way in annual 

 crops other than corn. Melons and other cucurbits are monoecious, 

 easily crossed under proper conditions and within a single species, and 

 large quantities of seed are produced. Very little is known concerning 

 the value of F\ hybrids between varieties as compared with parents, 

 but Hayes and Jones report preliminary experiments which indicate 

 that first generation cucumber crosses may frequently be expected to 

 exceed the higher yielding parent in yield. Only one out of four different 

 crosses failed to exceed the average of the parents in any character by 

 an appreciable amount. 



In tomato growing Wellington has shown that crossed seed is worth its 

 production as based on the increased value of a single crop without ref- 

 erence to origin of new varieties. He states that, while desirable results 

 have been obtained by crossing plants indiscriminately, "better results 

 would undoubtedly have been obtained if high-yielding mothers had been 

 selected for one or two generations previous to the first crossing." Toma- 

 toes are normally self-fertilized and, the high-yielding strains or pure lines 



