l8o BOTANY OF CROP PLANTS 



The distinguishing characteristics of the seven groups above 

 are shown in the following key : 



Key to "Species Groups" of Corn 



Each kernel enclosed in husks (glumes, lemma, palet); the ear is also 

 enclosed in husks; a rare form, considered by some to be the primitive 

 type, Zea tunicala (pod corn) . 

 Each kernel naked, not enclosed in pod or husk: 



Grains with popping properties; popping is due to the turning inside out of 

 the kernel through the explosion of the contained moisture when heat 

 is applied; pericarp is thick and tough; excessive proportion of horny 

 (corneous) endosperm; kernels and ears small, Zea everta (pop corn). 

 Grains without popping properties. 



No corneous endosperm, hence grains are soft; shaped like flint corn; 

 no indentation; the mummy corns of Peru, Mexico, and southern 

 United States probably belong to this group, Zea amylacea {soft 

 corn). 

 Corneous endosperm present. 

 Grains more or less wrinkled or shrivelled; kernels homy and trans- 

 lucent in appearance. 

 Grains horny throughout, Zea saccharala (sweet corn). 

 Grains with upper half horny and translucent, the lower half 

 starchy, Zea amylea-saccharata (starchy sweet corn). 

 Grains not wrinkled, smooth. 

 Starchy endosperm extending to top of kernel; corneous endosperm 

 at sides; shrinkage of starchy endosperm at top of grain causes a 

 drawing in of pericarp and hence the characterist c dent formed 

 (Fig. 64), Zea indentala (dent corn). 

 Starchy endosperm enclosed by the corneous endosperm; hence 

 there is no shrinkage of top of grain and no dent formed (Fig. 

 64), Zea indurata (flint corn). 



Zea amylea-saccharata (starchy sweet corn) is a group of 

 only botanical interest. Some seed of this was found in the 

 San Padro Indian collection by Dr. Palmer and sent to 

 Sturtevant in 1886. This seed was planted at Geneva, 

 New York, but the crop failed and the seed was lost. 



In Zea saccharata, the power to develop starch grains to 

 maturity has been lost. The starch that is formed remains 



