584 
Journal of Agricultural Research 
Vol. xxm, No. 8 
Studies by East (9, 10), Shull ( 36 ), East and Hayes (u), Jones (24), 
and East and Jones (12), with inbred strains or biotypes, showed that 
one of the effects of inbreeding in maize was a reduction of vigor and 
yield. Crossing unrelated inbred strains greatly increased vigor and 
yield. They (11) state that “ inbreeding always reduced the yield of seed 
and the height and delayed the time of flowering.** These workers pointed 
out that reduction in vigor due to inbreeding may or may not be accom¬ 
panied by pathologic symptoms (11). An illuminating discussion on 
inbreeding and hybrid vigor, or heterosis, together with an extensive 
bibliography, is given by East and Jones (12). 
In his investigations of the chlorophyll inheritance in maize,. Lindstrom 
(27) observed “a general correlation between chlorophyll factors and 
plant growth.** 
Ewing (13) obtained the following correlations with Funk Yellow 
Dent: 
Weight of grain and diameter of stalk... +0.393 dbo. 030. 
Weight of grain and breadth of leaf. -j- . 314 ± . 021. 
Weight of grain and height of seedlings. + . 219 ± . 037. 
Weight of grain and height of mature plants. + * 203 ± -025. 
He expressed the belief that very little use could be made of correla¬ 
tion in practical com breeding. He stated that there were rare cases in 
which the coupling of unit characters may assist the breeder in making 
selections at an early period of growth, but that the correlation in the 
fluctuating variability of two different characters is not likely to prove 
of much assistance. 
Pearl and Surface (30) made a study of growth and variability in 
sweet com in the summer of 1908. Growth measurements of a large 
number of plants were made at intervals of three and one-half days, 
beginning on June 11 and continuing until growth was completed. They 
found that the relative variability of height decreased as the season 
advanced and was on the average about 10 per cent lower in the matured 
plants than at the beginning of the season. During the tasseling period 
a marked increase in variability was noted, followed by a gradual decline. 
Their experiments demonstrated that plants relatively vigorous or weak 
at the beginning of the season tend to retain this comparative vigor. They 
regarded the differences in manner of growth as due to independent 
Mendelian factors distributed at random in the population of open- 
fertilized plants. 
Reed ( 31) studied the growth of a number of sunflower plants (Heli- 
anthus annuus L.). Measurements of the plants were made in centi¬ 
meters at 7-day intervals during the greatest period of growth. The plants 
were grouped in four equal numerical divisions called quartiles, on the 
basis of size. The season's study of the plants in these quartiles showed 
a well marked tendency to remain in a given quartile during the entire 
period of growth. Plants small atjmatimty generally had been small 
from the beginning and those large at maturity had a well-marked supe¬ 
riority from the start. Reed (31) found, as did Surface and Pearl (30), 
that height was determined by independent height factors distributed at 
random through the segregating population which he studied. 
Hughes (22) made extensive measurements of plants during two years, 
involving 828 ear rows. He found that plants highest at the first meas¬ 
urement made the most rapid averagejieight increment*per^plant*and 
produced the greatest yield. Plants from homy kernels made a more 
rapid height increment than plants from starchy kernels and also produced 
