THE MECHANICAL PENETRATION OF THE SWEET 
CORN PERICARP 
BY R. A. RUDNICK AND A. L BAKKE 
Hawkins and Harvey/ Rosenbaum and Sando/ and Hawkins 
and Sando ^ have used a modified Joly balance fitted with a 
puncturing needle to determine the force necessary to puncture 
the cells of the potato tuber, tomato, and certain smaller fruits. 
For the penetration of these tissues a relatively small force is 
necessary. 
However, it occurred to the authors that a similar mechanical 
penetrating device might be of service in determining the relative 
puncturing force of the pericarp of sweet corn. Inasmuch as 
the pericarp of the sweet corn is tough, it became necessary to 
employ a device where a greater pressure could be obtained than 
in the usual form of Joly balance. 
For this work then, the pulley and stand of a Ganong auxano- 
meter apparatus was fitted with scale pans of a chemical balance 
by means of braided linen cord of sufficient length to give a 
free uniform movement. To one of the stirrup hooks was at- 
tached firmly a glass needle having a diameter of 0.5 mm., this 
dimension being obtained by grinding a needle slightly larger 
with emery. The features described are apparent on examina- 
tion of figure 26. 
The portion of the pericarp used was the part back of the germ 
taken as far back from the tip as was possible. This layer was 
glued to a cork having a hole bored through it. Later a small 
piece of glass tubing having a diameter of 3.5 mm. was securely 
sealed with sealing wax. The matter of fastening each membrane 
to a cork naturally consumed considerable time as a new cork 
would have to be used for each test. To obviate this, the pericarp 
layer was placed between two pieces of glass tubing which had 
had their edges ground so that they would fit. This jointed 
1 Hawkins, I^, A., and Harvey, R. B. Physiological study of the parasitism ot 
Pythium deharyanum Hesse on the potato tuber. Jour. Agr. Research, vol. 18, pp. 
275-297. 1919. 
2 Rosenbaum, J., and Sando, C. R. Correlation between size of the fruit and the 
resistance of the tomato skin to puncture and its - relation to infection with 
Macrosporium tomato Cooke. Amer. Jour. Bot., vol. 7, pp. 78-82. 1920. 
' 3 Hawkins, Lon A., and Sando, Charles K. Bffect of temperature on the resist- 
ance to wounding of certain small fruits and cherries. U. S. Dept. A.gr. Bull. 
830. 1920. 
