Dec. 10,1917 Breeding Sweet Corn Resistant to the Corn Earworm 561 
PROLONGATION OP HUSKS 
The distance from the tip of the husks to the tip of the ear—in other 
words, the distance which the newly hatched larva, if it enters the tip 
of the husks, must travel before its depredations affect the ear—was first 
considered. This was the character thought to have been the chief 
cause of the immunity in the field varieties used as parents. 
Of all the characters measured this proved to be the most closely 
correlated with damage and the number of larvae, in both instances the 
correlation being negative. The interprogeny correlation between pro¬ 
longation and damage was —0.71 ±0.06 and the regression of damage 
on prolongation was 1.02—that is, with an average increase of 1 cm. in 
* the prolongation an additional 1 per cent of the crop was saved. The 
meaning of this regression of 1.02 may be further examined by com¬ 
paring the damage in the progenies with the greatest and least pro¬ 
longation. There were 14 progenies whose mean prolongation was 
less than 5 cm., the average prolongation of this group being 2.9 cm. 
The average damage in this group of progenies was one grade, or 10 per 
cent of the total crop. The 12 progenies with the greatest average 
prolongation, all of which were 6 cm. or over, had an average prolonga¬ 
tion of 7.7 cm. and a damage of 0.5 grades, or 5 per cent. Thus, an 
average increase of 4.8 cm. in prolongation was accompanied by an 
average reduction of 5 per cent in damage. 
The correlation of 0.71 between prolongation and damage is suffi¬ 
ciently close to justify the hope that the method followed is satisfactory 
and that by increasing the prolongation through hybridization or selec¬ 
tion substantial reductions in the damage can be secured. A closer 
study, however, indicates that the relatively close correlation between 
prolongation and damage is probably not to be completely explained 
on the basis of a simple physical protection. The chief reason for 
doubting the apparent direct relation between prolongation and damage 
is that prolongation appears to have nearly as much affect on the number 
of larvae as on the amount of damage, the correlation being — o.6o±o.o8. 
Since all the larvae found inside the husks were counted, whether they 
had gained access to the ear or not, prolongation can hardly be held to 
have reduced the number of larvae in any such manner as it might be 
expected to reduce the damage. 
If, to gain access to the ear, the larva must eat its way down the 
silks, prolongation would seem necessarily to be a very effective protec¬ 
tion. If, on the other hand, larvae may force their way between the 
silks and simply crawl to the ear, prolongation would be much less 
effective. A very large proportion of the eggs are laid on the silks soon 
after they appear. The eggs hatch in two or three days and the newly 
hatched larvae are only about 1.5 mm. long. 1 From the fact that 
1 Quaintancb A. L., and Brurs, C. T. Op. cit. 
