38 VALUE OF FIRST-GEXERATIOX HYBRIDS IX CORX. 



One difficulty, however, with this reciprocal use of male and female 

 parents would arise unless the varieties agree in length of season. 

 Xo difficulty would be experienced in securing perfect pollination in a 

 short-season variety used as the female parent, but if such a variety 

 were expected to serve as the male parent the tendency to the early 

 shedding of the pollen might leave little or none available for ferti- 

 lizing a later variety used as a female parent. 



The following directions, which have been sent out to several 

 cooperative experimenters, give a concrete example of one of the 

 ways in which the value of first-generation hybrids may be deter- 

 mined : 



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

 plats. Varieties may be designated as Xo. 1 and Xo. 2, the plats as A and B. The 

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



It should be kept in mind that the increased \-ield can be expected only for the one 

 year immediately following that in which the cross is made. 



Plat A is planted with alternate rows of Xo. 1 and Xo. 2. The rows planted with Xo. 

 2 are to have all plants detasseled. The crop of Xo. 1 and Xo. 2 is to be saved sepa- 

 rately. 



Plat B is planted entirely with variety Xo. 2 and has alternate rows detasseled. 

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



At harvesting there will be the following lots of seed: 



(1) Plat A. Variety No. 1, field-pollinated. 



(2) Plat A. Hybrid between Xo. 1 and Xo. 2. 



(3) Plat B. Variety Xo. 2, field-pollinated. 



(4) Plat B. Variety Xo. 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 j-ield. 



A comparison of the j-ield from these four lots of seed the following year should show 

 the }-ield 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 plat B can not be proWded, seed of variety Xo. 2 should be held for planting the 

 following year in comparison with variety Xo. 1 and the hybrid seed. 



If it is considered important to have the crop of a uniform color, yel- 

 low and white varieties should not be crossed, for the grains will be of 

 different colors in the year foUowing the cross. Crosses between dent 

 and flint or between these and sweet corn would also result in a lack of 

 uniformity with respect to the character of the seed. That such differ- 

 ences should occur while the other characters remain so nearly uni- 

 form may appear remarkable, but is explained by another of the 

 pecuhar habits of the corn plant. UnUke most other plants the seeds 

 of corn show an immediate effect of pollen (xenia).* If a white- 

 seeded varietv is crossed bv one with vellow or black seeds, the new 

 seeds that are produced show the color of the male parent. 



" For a discussion of xenia, see Webber, H. J., Bulletin 22, Division of Vegetable 

 Physiology and Pathology, U. vS. Dept. of Agriculture, 1900. 

 191 



