8o 
J. ROSENBAUM AND CHARLES E. SANDO 
tomato was placed on the stand of the instrument; the needle was lowered 
until it just touched the surface of the tomato and watched closely until a 
quick drop showed that it had penetrated the skin of the fruit. The reading 
on the scale of the instrument was then taken. From this reading the pres- 
sure required to puncture the tomato skin could be calculated. 
To illustrate the method of calculation, let us suppose the scale reading 
at which penetration took place on a fruit to be 31.00. The upward pull 
of the stretched spring representing this number as the reading on the scale 
was determined by counterbalancing with weights placed on the pan. 
This pull equalled 7.42 grams. The entire weight of the glass rod, with the 
needle, was 12.04 grams. The pressure necessary to puncture the skin was, 
therefore, the difference between the downward force and the upward force, 
or the difference between 12.04 742, or 4.62 grams. The pressure 
necessary, therefore, to penetrate the skin of a particular fruit with a needle 
which was 78 microns in diameter amounts to 4.62 grams. 
Where tomatoes of different sizes were used, a total of five fruits of 
each size were punctured. Since the hardness over the entire fruit varies 
somewhat, it was thought advisable to make part of the punctures around 
the style end and an equal number around the stem end. Generally ten 
punctures were made on each fruit. The average of these readings gives 
fairly accurately the pressure necessary to puncture a particular fruit. 
As a general rule, it was found that the stem end was slightly harder than 
the style end. The fruits were picked and brought into the laboratory 
where they were divided into two lots, each lot containing fruits of the same 
maturity. One lot was used for determining the resistance of the skin to 
puncture while the other lot was washed, placed in disinfected moist cham- 
bers, and inoculated by spraying with a suspension of Macrosporium spores. 
In addition to the inoculations made on fruits brought into the laboratory, 
additional inoculations were made in the field on fruits growing on the 
vines. In this case the fruit was sprayed with a suspension of spores and 
covered with a glazed paper bag for a few days. No difference in the 
amount of infection was obtained whether the fruit was inoculated in the 
Table i. Showing the Relation Between Resistance of the Skin to Puncture and Macro- 
sporium Infection on Different Sized Tomatoes * 
Size 
Color 
Circumference in Inches 
Average Weight 
in Grams 
Pressure in Grams 
Necessary to Puncture 
Fruit (Average of 50 
Stabs) 
Percentage of Positive 
Infection with Macro- 
sporium 
A. ... 
B. ... 
C. ... 
D. ... 
E. ... 
F 
Red 
Green 
Green 
Green 
Green 
Green 
Green 
5-19 
5.87 
5.70 
4.08 
3.52 
3.26 
2.66 
0 
0 
0 
37 1/2 
85 5/7 
72 8/1 1 
100 
10 3/4-1 1 1/4 
7 3/4- 8 1/4 
61/2-6 3/4 
5- 5 1/2 
4- 4 1/2 
3- 3 1/2 
254.87 
115. 12 
66.36 
34.22 
18.17 
7-39 
* Temperature of tomatoes when punctured, 23° C. 
Needle used, 78 microns in diameter. 
