174 



BOTANY OF CROP PLANTS 



pollen are wrinkled. If xenia does not occur, the results of 

 the mixing will not show up until the second year. Hence, 

 ordinarily even though an ear of corn appears uniform, the 

 separate kernels may have different heredity. The only way 

 of testing its purity is to plant the grains and observe their 

 progeny. Of course in this test, care must be taken to pre- 

 vent strange pollen from blowing in. This is practically ac- 

 compHshed by isolating the test plots. 



Results of Self-fertilization in Corn. — If our ordinary 

 field strains of corn are self-fertiHzed for several generations 

 the yield is considerably reduced. However, as a result of 

 this inbreeding, we may be sure that all the kernels on an ear 



Fig. 64. — Corn (Zea mays). ^, median lengthwise section, cut parallel to 

 broad surface, of grain of dent corn; B, cross-section of same through the 

 embryo; C, section as in A of flint corn. 



have the same hereditary qualities. Furthermore, artificial 

 self-fertiHzation for five or more successive years results in a 

 strain that is not so complex in its characters, that is, a race 

 which is comparatively uniform and pure. 



The Mature Grain of Com. — The mature grain of corn 

 varies considerably in shape (Fig. 64). In most varieties, 



