466 



SCIENCE 



[N. 8. Vol. XXIX. No. 742 



a zone of white stareliy matter extending 

 from the tip to the cap, where it forms a layer 

 varying in thickness in different varieties. 

 The shrinkage of this cap starch forms the 

 indentation of the kernel. In the flint corns 

 this soft starch at the cap is replaced hy 

 corneous starch, thereby giving the outer por- 

 tion of the kernel a smooth appearance. Be- 

 sides this absolute difference, most dent and 

 flint varieties differ in other characters, al- 

 though a few intergrading strains are found. 

 In the first place, dent corns are found that 

 possess from twelve to twenty-eight rows of 

 kernels, while the older flint types have but 

 eight rows. It is true that there are genuine 

 dents and true flints that tend toward the 

 production of twelve rows, but below this 

 number with the dents, and above it with the 

 flints, continual reversions indicate a hybrid 

 condition. Dent corns are little given to till- 

 ering, while with flint corns it is character- 

 istic. This trait is partly a physiological re- 

 action due to the greater amount of soil 

 fertility required by the large main stalk of 

 the dent varieties, and partly an inherent 

 trait capable of hereditary transmission. 

 Flint corns are further characterized by the 

 manner in which the ends of the spathaceous 

 bracts (husks) enclosing the pistillate flowers 

 are expanded into leafy parts from one to two 

 feet long. In the dent corns these appendages 

 are absent or only slightly developed. 



The bearing of these opposite features in 

 the dent and the flint corns on the matter in 

 hand, is that sweet corn with its numerous 

 varieties runs the whole gamut of these char- 

 acters. Stowell's Evergreen, a large sweet 

 variety with from sixteen to twenty-four 

 rows, is an example of a " dent " sweet corn, 

 while the Golden Bantam and Black Mexican, 

 two small eight-rowed varieties, are examples 

 of " flint " sweet corns. These varieties are 

 typically dent and flints, respectively, in every 

 character except starchiness. Moreover, when 

 the character of starchiness is brought into 

 kernels of these varieties by pollination with 

 either dent or flint pollen, the hybrid kernels 

 formed are indistinguishable from pure dent 

 and pure flint kernels, respectively. It seems 

 to make no difference with either variety 



whether dent or flint pollen is used, for, al- 

 though the starchy character appears in the 

 individual kernel as zenia through double 

 fertilization, the dent and flint characters ap- 

 pear to be largely — ^I do not say entirely — 

 determined by the plant character possessed 

 by the female parent. 



To determine whether Black Mexican sweet 

 com carries the " flint " character even though 

 it has no "starch" character, it was crossed 

 on a white dent variety. Both ts^pes were 

 pedigreed corns ; that is, they had been grown 

 in isolated plots for at least five years, conse- 

 quently they may be considered to have been 

 pure. To remove all doubt on this point, 

 however, kernels from the same ears that pro- 

 duced the plants that were crossed were in- 

 bred. The inbred ears all proved to be true 

 to their respective characters. 



The F^ generation of this cross, although it 

 showed the regular Mendelian ratio of starchy 

 and non-starchy kernels, consisted both of 

 dent and of flint ears. Neither the flint char- 

 acter nor the dent character was dominant, 

 hence the appearance of the two types. We 

 are forced to the conclusion that the flint 

 character was brought into the combination 

 by the sweet com parent, and became mani- 

 fest when it met the " starch " character of 

 the dent com parent. In lilce manner 

 Stowell's Evergreen was shown to carry the 

 " dent " character, by crossing with an eight- 

 rowed starchy flint variety. The F^ genera- 

 tion contained several dent ears which could 

 only have been produced by the " starch " 

 character of the flint variety meeting the 

 " dent " character of the sweet variety. 



It is evident that the internal structure of 

 the corn kernel is based upon several unit 

 characters. There are different patterns of 

 corneous starch which produce pop, flint, dent 

 and starchy varieties. These units seem to 

 be partly independent and partly dependent 

 on starchiness and on shapes of pericarp. 



It may also be noted that evidence is ac- 

 cumulating that the above facts regarding 

 sweet corn are largely accountable for the 

 marked superiority in sweetness of most small 

 sweet com varieties. The " dent " sweet va- . 



