BULLETIN OF THE BUSSEY INSTITUTION. 17 
the act of popping. He argued that ‘‘ the popping is apparently 
due to the bursting of the starch grains. Only the flinty varieties 
‘pop.’ ‘These are more compact in structure, and as the starch 
grains expand with the heat the hard exterior is burst.” * 
Mr. M. I. Wilbert,t also, has insisted on the fact that the 
popping of corn is due to the explosion of the starch grains by 
~ steam generated within them on the application of heat. ] 
A more elaborate study of the causes of corn popping has been 
made recently by Professor Henry Kraemer,{ of Philadelphia, 
who has shown by careful microscopic examinations of many 
varieties of maize that there are such marked differences in the 
structure of the several parts of the kernels that at least three 
distinct kinds of corn grains may be distinguished according to 
the character of their endosperms. In the pop-corns proper the 
endosperm is more or less translucent and horny, and the cells in 
it contain closely arranged polygonal starch grains from 7 to 18 
microns in diameter and having a central rarified area from 2 to 7 
microns in diameter. ‘'On examining the endosperm of the 
popped grain it is observed that there has been considerable 
alteration in the starch grains and cell walls. . . . The struc- 
tural characteristics of the starch grains in, the altered areas of 
the different pop-corns would seem to indicate that the popping 
of the grain of corn results from the expansion of the individual 
starch grains, the degree of expansion depending upon the rela- 
tive amount of water and air in the grains. As an illustration of 
this it may be stated that perfectly fresh pop-corn or pop-corn 
that has been soaked in water for twenty-four hours will pop but 
little in the true sense of the word. On the other hand, a pop- 
corn which was seven years old, but had not lost its germinating 
power, would not pop unless first soaked in water and then 
allowed to dry for from four to twelve hours. That this property 
probably resides in the starch grains is further shown by the fact 
that pieces of the pop-corn grain will pop.” 
This last statement of Professor Kraemer, that pieces of pop- 
corn will pop, suggested to me the following experiments : — 
* See page 108 of William H. Brewer’s Report on the Cereal Production 
of the United States, in Tenth Census of the U.S. 1880, Statistics of Agri- 
culture, page 483. 
+ American Journal of Pharmacy, 1903, 75. pp. 77, 100. 
t Science, May 1, 1903 (n.s.), 17. 683. 
