Corn Investigations 
11 
yield of grain was 35 per cent of the original corn. Individual 
yield tests of 32 inbred strains of Hogue’s Yellow Dent corn for 
briefer periods indicate considerable variation in grain yield. 
In one experiment, the use of the lowest yielding pure lines as 
one of the parents resulted in hybrid yields of 13.5 bushels less 
per acre than where both inbred parents were relatively higher 
yielding. In another two-year test with eighteen hybrids, 
groups of the five highest, eight intermediate, and five lowest 
yielding hybrids produced relative grain yields of 100, 89, and 
65; while the average grain production per plant of the inbred 
parent strains of these three groups was respectively 100, 86, 
and 65 per cent. This suggests that crossing the more produc- 
tive pure lines is likely to result in the most productive hybrids. 
16. In a four-year test of eight F n hybrids between pure 
lines, the average yield surpassed the original corn 17.2 per cent 
while the most productive hybrid excelled the original by 30 per 
cent. A perplexing question arises from the fact that during 
one year of this test the same eight hybrids averaged 9 per cent 
less than the original. Altho the grain yields of these hybrids 
averaged- 9.7 per cent more than the original corn during 1915 
and 1916, their plant development was smaller. They were four 
inches shorter and had 18 per cent less leaf area. This does not 
suggest a correlation between grain production and vegetative 
vigor as measured in plant size. It doubtless indicates both the 
complete elimination of some deleterious factors which were 
present in the original variety and also the isolation and recom- 
bination of superior factors thru the inbreeding and hybridizing 
processes. 
17. During two years, 29 F n hybrids between pure lines 
were compared with the original corn from which they were de- 
veloped. The inbred parents of these hybrids were derived 
from plant types which had been partially fixed by continuous 
plant type selection for either a high proportion or a low pro- 
portion of leaf area per unit of mature dry plant weight. The 
relative grain yields of the' (1) original corn, (2) low leaf area 
hybrids, (3) high leaf area by low leaf area hybrids, and (4) 
high leaf area hybrids Avere 100.0, 112.0, 107.4, and 100.9. The 
highest yielding individual hybrid surpassed the original corn 
34 per cent. The correlated low leaf area ratio and slender, 
smooth, horny ear and low actual leaf area on the one hand, and 
the high leaf area ratio and large, rough, starchy ear and high 
actual leaf area on the other hand, were retained thruout the in- 
breeding process and transmitted to their hybrid offspring. 
