334 LINDSTROM, GENETICAL RESEARCH WITH MAIZE : 
the development of endosperm color, yellow color being dominant to 
white or colorless (East and Hayes 1911). In this case however the do- 
minance is incomplete, being modified by the number of doses of the 
yellow factor. 
The endosperm tissue, being the result of a triple fusion (two £ nuclei 
and one gnucleus), offers an interesting example of the cumulative ef- 
fect of genetic factors. The following are the possible combinations af- 
forded by such a triple fusion: — 
Y Y Y — dark yellow 
Y Y y — yellow 
y y Y — light yellow 
y y y — white 
Reciprocal crosses of yellow and white maize give slightly different 
shades of yellow for this reason. 
In addition to this simple Yy factor pair there are others controlling 
endosperm color. Ratios of 15 yellow (variable shades) to 1 white are 
known, and 63 : 1 ratios have been reported. Rare cases of a dominant 
white endosperm have also been found (White 1917). 
The texture of the maize endosperm is a source of much genetic va- 
riability. Most of the commercial varieties of corn are differentiated by 
their endosperm characteristics. These include the dent, flour, pop, 
flint, and sweet corns. 
Sweet corn. — Certain varieties of maize that are used for canning 
purposes and table use are characterized by a distinct wrinkling of the 
grain when mature. It is assumed that this wrinkling of the kernel is 
caused by the drying of the grain in which the sugars have not been 
completely transformed into hard starch. This horny strarch would 
prevent the grain from losing its shape as it does in flint varieties. 
The sweet corn character is a simple recessive in inheritance to the 
starchy type (dent, flint, or pop corn) as well as to the soft floury and 
waxy varieties. The degree of wrinkling in sweet corn kernels is modi- 
fied to some extent by the texture of the endosperm. For example, cer- 
tain varieties of sweet corn are merely latent flint corns, other latent 
dent or flour corns. This fact is clearly brought out in crosses with such 
types. 
Crosses of sweet and waxy maize reported by Collins and Kempton 
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