14 BULLETIN 925, TJ. S. DEPARTMENT OF AGRICULTURE. 



the area available for photosynthesis has been reduced somewhat. The 

 degree of this reduction is yet to be determined, but with the ex- 

 ception of this reduction which, under certain conditions, may be 

 beneficial, there should be no other physiological difficulties in com- 

 bining high productivity with brachytic stature. 



Genetically, however, more difficulties are to be expected. Yield of 

 grain, like most quantitative characters, is one of those relatively 

 unstable characters difficult to recover from hybrids involving small- 

 eared varieties. If only 10 factors are involved in maximum grain 

 production, all 10 of these would be .expected to occur in homozygous 

 combination with brachytic culms in an F 2 hybrid only once in 

 4,195,304 plants. To be reasonably certain of securing the combi- 

 nation in an F 2 hybrid, at least 12,585,912 plants should be grown. 

 It is, however, an unfortunate fact that probably many more than 

 10 factors are involved. The form of the inflorescence alone can be 

 resolved into several component parts, such as length, diameter, num- 

 ber of seeds, size of seeds, number of rows, volume, and weight of 

 seeds, all of which are known to be inherited separately, and even 

 these subdivisions are far from being simple characters. 



With the several advantages, the commercial value of the bra- 

 chytic variation depends upon the success with which the shortened 

 internocles may be combined with the grain production of the stand- 

 ard dent varieties. It is not unlikely that if such a combination were 

 effected the value of the strain would be appreciated in areas out- 

 side the regions of extreme climatic conditions. The brachytic char- 

 acter is one which reappears in the per jugate generation of hybrids^ 

 and the possibility of combining the dwarf stature with the high pro- 

 ductivity of commercial varieties will be considered. 



INHERITANCE OF BRACHYSM IN HYBRIDS WITH COMMERCIAL 



VARIETIES. 



BRACHYTIC X BOONE. 



In an effort to combine the brachytic character of the culm with 

 the high productivity of commercial varieties, several crosses have 

 been made. Two crosses were made with the Boone County White 

 variety, and a few first-generation plants of each cross were grown 

 in the greenhouse and self -pollinated. Three ears resulted, and a 

 progeny of each of these, as well as a large population of the first 

 generation, was grown in the field at Lanham, Md. The first-gen- 

 eration plants grown in the field were fully as large as the Boone 

 parent and remarkably uniform. A number of characters were 

 measured, as shown in Table III. 



The three second-generation progenies segregated into normal 

 and brachytic plants, with well-defined classes closely approximate 



