EARLY IDEAS ON INBREEDING AND CROSSBREEDING 13 



King. The average height of the parental stocks was 8 feet 3 inches while 

 the cross averaged 12 feet 4 inches, an increase of 4 feet 1 inch. 



The next year Webber (1901) called attention to the marked loss of vigor 

 in corn from inbreeding. From 100 stalks of selfed corn he obtained 46 

 ears weighing 9.33 pounds, while from 100 stalks obtained from crossing 

 different seedlings he obtained 82 ears weighing 27.5 pounds. When he 

 attempted to "fix" his Cuzco-Hickory King hybrid by selling he got a great 

 loss of vigor and almost complete sterility, but when he crossed the different 

 seedlings there was little loss of vigor. He concluded that to fix hybrids 

 one should not self the plants. 



In 1900, the discovery of Mendel's long-forgotten paper was announced. 

 Both Hugo de Vries and C. Correns, two of the three discoverers of Mendel, 

 published papers on Zea mays and all future work on Indian Corn was on a 

 somewhat different level. 



SUMMARY OF KNOWLEDGE OF HYBRID VIGOR AT 

 BEGINNING OF 20th CENTURY 



1. Inbreeding reduces vigor and produces many defective and sterile indi- 

 viduals which automatically discard themselves. 



2. Cross breeding greatly increases vigor both in interspecific and inter- < 

 varietal hybrids. Crossing two inbred stocks restores the lost vigor and 

 frequently produces more vigor than the stocks had originally. 



3. All inbred stocks do not produce the same amount of vigor when crossed. ^ 

 Certain crosses are far more effective than others. 



4. The simplest method of hybridizing Zea on a large scale is to plant two 

 stocks in alternate rows and to detassel one stock. The hybrid corn grown 

 from the detasseled stock produces the great yields. 



5. Hybridization must be secured each generation if the yield is to be kept 

 up, although a second generation of open pollinated corn may still be 

 better than the original parental stocks. 



6. In inbreeding, both parents are apt to have the same defects which are V 

 intensified in the offspring. The cause of hybrid vigor is that in crosses 

 the parents usually have different defects which tend to compensate for 

 each other in the immediate progeny. 



7. The fact that hybrid vigor in Zea is not permanent but decreases if the 

 hybrids are open-pollinated, seems to be related to the fact that fruit 

 trees, whose desirable qualities are preserved by vegetative propagation, 

 produce seedlings which are inferior. 



