Journal of Agricultural Research 
Vol. VII, No. 6 
284 
potash-chlorin ratios and show an inverse relation to his chlorin-content 
figures, this relation does not hold for the good-burning samples, except 
in the case of the Treatment VI previously referred to. The relative 
inferiority of the poor-burning samples in this series is doubtless traceable 
in part to their high content of chlorin, which element is commonly re¬ 
puted to be antagonistic to combustion. 
Though a more or less definite correlation seems to exist in the tobacco 
studied between the burning qualities and grain aggregation, for which a 
tentative explanation has been advanced, no reason is evident at this 
time for the apparent relation between the low degree of aggregation and 
the high chlorin content of the poor-burning samples. It is hoped that 
future work may throw some light upon this phase of the problem as well 
as upon other possible factors affecting grain formation in tobacco. 
DEVELOPMENT OF THE GRAIN 
While the opportunity has not been offered for a thorough study of the 
process of formation and aggregation of the grain in the leaf, preliminary 
investigations upon material referred to in footnote on page 279, as well as 
upon various kinds of tobacco observed in the laboratory, indicate that 
the grain substance is not present in crystalline form in the living, green 
leaf. These observations prove that the formation and development of 
the grain bodies are concomitant with the process of curing, and there 
are indications that the aggregation of the grain substance continues 
during fermentation (compare PI. 17, fig. A, E, G). 
At Red Lion, Pa., on September 22, 1914, four days after harvesting, 
samples of tobacco were becoming flecked near the margins of the leaves 
with the yellow mottling characteristic of the early stages of curing. 
In this condition microscopic examination showed the absence of grain 
bodies and also that the protoplasmic contents of the cells were still intact. 
In the later stages of yellowing and with the apparent death and disorgan¬ 
ization of the protoplasm, just before the development of the brown 
color, highly refractive droplets appeared in the cells. Upon attempting 
to dehydrate a piece of such a leaf in alcohol minute crystals appeared in 
these droplets. In the next stage—that is, at about the first indication 
of a brown color in the leaf—the droplets had enlarged and become de¬ 
cidedly viscid, and each showed upon examination with polarized direct 
sunlight conspicuous crossed extinction bands and presented the appear¬ 
ance of spherites. Upon dehydration at this stage they developed no 
small crystals. As the browning progressed, certain of the bodies seemed 
to differentiate within themselves, without artificial dehydration, a 
nucleus of crystals of definite though not identifiable form. The sub¬ 
stance of the droplets in which no crystals had formed seemed to migrate 
toward those which had produced crystal nuclei, increasing by accretion 
the crystalline mass until groups of several cells each had become literally 
