570 
Journal of Agricultural Research 
Vol. XI, No. ii 
delayed in sweet varieties. It is possible that in these particulars the 
immune strains might tend to resemble the field parent. So far as has 
been observed, this has not been the case. Both the percentage of sugar 
and the retardation of transformation are very difficult to measure accu¬ 
rately, for, in addition to the labor of chemical analysis, the problems 
are seriously complicated by variations due to the time when the analysis 
is made and by individual variation. It would seem that, to compare 
two strains with respect to these characters, it would be necessary to 
analyze a sufficient number of samples of each variety to secure a reliable 
average and to repeat this entire process at short intervals, beginning 
soon after fertilization and continuing until the sugar content was prac¬ 
tically constant. 
The only evidence obtained on these points is that when gathered at 
the proper time the immune strains were pronounced by a number of 
different observers to be fully as sweet as the parent sweet varieties, and 
that in the regression of maturity on days silking to harvest no con¬ 
sistent differences were found between the immune strains and com¬ 
mercial sweet varieties. That sweet segregates from a cross between 
sweet and field varieties are not deficient in sugar is shown by the work of 
Pearl and Bartlett, 1 who found the percentage of sugar in the F 2 segre¬ 
gates of a sweet with dent cross to be higher than in the sweet parent. 
CONCLUSIONS 
In the southern part of the United States and throughout the Tropics 
very little sweet com is grown. The chief reason for this is believed to 
be the ravages of com earworm (Chloridea obsoleta Fab.). 
Attempts to grow sweet varieties in the South usually result in an 
almost complete destruction of the crop by corn earworms. The native 
field varieties, on the other hand, escape with relatively slight injury, 
and are largely used as a substitute for sweet com. 
The most obvious difference between sweet and field varieties that 
might be expected to affect the activities of the com earworm is the 
extent to which the ears are protected by husks. Sweet varieties gen¬ 
erally have the husks poorly developed. A possible reason for this may 
lie in the fact that in the northern part of the Com Belt one of the most 
desired characteristics in sweet com is an early season. Generally 
speaking, early varieties produce few leaves and few leaves are asso¬ 
ciated with few husks. There is, therefore, a simple explanation of why 
commercial varieties of sweet com have poorly protected ears and the 
poorly protected ears of sweet varieties afford at least a theory as to 
why they are especially susceptible to the ravages of the corn earworm. 
With these facts in mind the problem was to combine the well- 
protected character of the ears of southern varieties of field corn with 
1 Pearl, Raymond, and Bartlett, J. M. mendelian inheritance of certain chemical charac¬ 
ters in maize. In Ztschr. Indukt. Abstam. u. Vererbungslehre, Bd. 6, Heft i, 2, p. 1-28,1 fig. 1911. 
