278 
Journal of Agricultural Research 
Vol. VII, No. 6 
is not enough grain-free tissue to act as kindling material and produce the 
temperature required to ignite the almost solid mass of grain substance 
characteristic of poor-burning tobacco. 
While several theories have been set forth 1 concerning the bum of to¬ 
bacco, for the most part chemical and differing from the hypothesis just 
advanced, an instance in favor of the present explanation is found in the 
case of the notoriously poor-burning 1909 crop of Pennsylvania. In this 
tobacco the grain substance is abundant, but it occurs in the tissue as an 
almost solid sheet, showing very poor aggregation into definite grain 
bodies (PI. 17, fig. B). Again, flue-cured tobacco, which is always con¬ 
sidered a poor-burning type, is entirely without grain aggregates. In this 
tobacco there is a small amount of grain substance (PI. 17, fig. C) com¬ 
pared with cigar types, and it appears to be deposited very rapidly in 
the form of a haze of minute crystals throughout the tissues of the leaf. 
It is thought that the rapid-curing method employed with this type is 
responsible for this condition, inasmuch as the same kind of tobacco, 
grown in the same region and air-cured instead of being subjected to 
heat, shows to some degree the aggregation of the grain substance into 
definite bodies. In this connection it may be said also that Connecticut 
tobacco (PI. 17, fig. D), which as a rule shows an excellent bum, also 
possesses a high degree of aggregation of the grain substance. 
In connection with some investigations concerning the cause of the 
defects in the burning quality of York County tobaccos jointly pursued 
by the Office of Tobacco and Plant Nutrition Investigations and the 
Pennsylvania Agricultural Experiment Station 2 working cooperatively, 
a certain degree of correlation of grain formation and burning quality 
has been found. The tobacco was grown at Red Lion, Pa., during the 
seasons of 1913 and 1914 in duplicate plots upon which nine different 
fertilizer treatments, identical for the two years, were used to determine 
their influence upon the burning quality of the product. The material 
used for microscopical investigations was comparable to that upon which 
the bum and other factors were determined. In preparing the material 
for examination with the microscope, disks were cut from the leaves 
t Gamer discusses (3) the more important contributions concerning # the bum of tobacco. Of the 
two physical theories thus far advanced, the one sought (1) to correlate the burning quality of to¬ 
bacco, at least in part, with such anatomical features of the leaf as the number of rows of cells, the size of 
intercellular spaces, etc., while the other attributes (6) a beneficial influence to the action of potash salts 
of the organic acids in swelling to many times their original bulk and thereby yielding a porous mass of 
finely divided carbon when decomposed by heat. The chemical data given herewith do not support the 
latter theory, since the organic acids are largely localized in the grain, and only a small portion of the potas¬ 
sium is present in these bodies. This indicates that the greater portion of the potassium in the leaf is not 
in combination with the organic acids. No experimental work has been done by the writer concerning the 
former theory, though it is believed that in view of the results published herein and the fact that in cigar 
tobaccos the intercellular spaces are obliterated and the cell walls collapsed during the fermentation process 
little ground would be found for its substantiation. 
2 A report of this cooperative work by Dr. William Frear, Chemist and Vice Director of the Pennsylvania 
Agricultural Experiment Station, will appear in the annual reports of that institution for 1913-14 and 
1914-15, 
