354 GENETICS IN RELATION TO AGRICULTURE 
Collins to be those of Beal (Michigan, 1878-1882), Ingersoll (Indiana, 
1881), Sanborn (Maine, 1889), and of Morrow and Gardner (Illinois, 
1892). All of these crosses were made between commercial varieties and 
in each case the hybrids outyielded one or both parents. Then came the 
work of Shull and of East (1908) with inbred strains and the crosses between 
them, both investigators obtaining an increase in yield in the hybrids 
over that of the original stock. Following this the United States Depart- 
ment of Agriculture conducted experiments on an increasingly extensive 
scale and included work with the most distinct types as well as commercial 
varieties and inbred strains. More recently various experiment stations 
have conducted similar investigations. 
Crossing inbred strains or biotypes produces the most striking results 
because the rate of increase in vigor in the F; hybrids over the inbred 
strains is enormous (as much as 250 per cent. over the average of the 
parents). Of course it is much greater in some cases than in others be- 
cause of the inherent differences between different biotypes. East worked 
with biotypes of four different varieties and secured an average increase 
of 73 per cent. in all crosses. The data on inbreeding the Leaming 
dent variety are summarized by East and Hayes in Table LI. It will be 
noted that two of the strains were not grown as second inbred generations 
Taste LI.—Errect or INBREEDING IN STRAINS OF LEAMING Dent MaizE 
Yield in bushels of shelled corn per acre and years in which grown (After East and 
Hayes) 
Generations inbred 
| t} | | 
| 1 | 2 | 3 | 4 | 6 
| 
Parent Strain 
variety number 
ou 
5 | 391 95:2. || 6779: ||| "S00" | 8777 
? | (1906) | (1908) | (1909) | (1910) | (1911) 
| | 46.0 | 63.2 || 25.4 
| (1908) | (1910) | (1911) 
yl Gone 59.3 
BEDS eet) 59.7 | 68.1 41.3 
| (1909) | (1910) | (1911) 
88.0 (1905) 
; 42.3 5127 35.4 | 47.7 26.0 
| (1906) | (1908) | (1909) | (1910) | (1911) 
| PEs 16.5 2.0 
0 38.1 32.8 46.2 || (4909) | (1910) | (1911) 
06 907 08 
PEO BLOF) I LOGE rN rata mecen 2.0 
(1909) | (1910) | (1911) 
Digitized by Microsoft® 
