RESULTS WITH HYBRIDIZATION 



111 



CROSSING BIOTYPES 



81. However, these "elemental strains" are low in yield, 

 but are stimulated to yield by hybridizing. The effect 

 of hybridizing as a stimulus is shown in the following 

 table : — 



TABLE XVII 



The corn is at once restored to full vigor by hybridizing. 

 The yield appears to decrease somewhat the second 

 year, probably because a certain percentage of the plants 

 have returned to a pure-type (homozygous) state. 



Under natural conditions there is a certain percentage 

 of both inbreeding and close breeding. This has led to 

 the suggestion that means should be used to insure that 

 all seed used is first-generation hybrid. This can be 

 accomplished by alternating rows of pure strains and 

 detasseling every alternate row, saving seed from the 

 detasseled rows. 



CROSSING VARIETIES 



82. Several investigations have shown an increase from 

 the use of first-generation hybrid seed, when two varieties 

 have been crossed. The following table, summarized from 



