Nov. 6, 1916 
Grain of the Tobacco Leaf 
285 
petrified and formed a solid grain body. Definite grain was formed in 
leaves of average maturity in nine days after the tobacco was harvested. 
It is thought that the migration of the still viscid substance was 
brought about by diffusion, through the dead and permeable proto¬ 
plasm, set up by a lowering of concentration in the immediate vicinity 
of the developing crystal nuclei. Under ideal curing conditions it is prob¬ 
able that this process results in the aggregation of all, or nearly all, 
of the grain-forming substance into definite bodies, leaving around each 
a zone of cells largely free from that material. It is believed that under 
these conditions the number of grain bodies developed in a given area is 
dependent upon the number of crystal nuclei formed. The factors which 
determine the number and distribution of the latter are not known. 
It is thought, however, that the rate of desiccation and the degree of 
maturity of the curing leaves may be of importance in this respect. 
The behavior of the grain material in the flue-cured tobacco seems to 
support the idea that the rate of drying is a factor in grain development. 
In the completely cured leaf of this type the substance which would have 
formed more or less definite grain bodies under ordinary air-curing con¬ 
ditions apparently has been thrown down in crystalline form by the 
rapid curing and drying characteristic of the method, in the first droplet 
stage referred to above, resulting in a haze of minutely crystalline mate¬ 
rial in all the cells. Even Connecticut tobacco, when cured very rap¬ 
idly (“hayed-down”), frequently shows poor burning qualities. Again, 
in the poor-burning crop of tobacco produced in Pennsylvania in 1909, 
which was a “dry-weather crop,” the grain material failed to become 
well aggregated. It seems probable that either a low percentage of 
water in the tissues or an abnormally large quantity of grain-forming 
substance in solution in the cell sap at the time of harvesting, or both, 
must have resulted in the formation of an unusually large number of 
crystal nuclei in a given area, especially if weather conditions were such 
as to cause rapid dessication in the early stages of curing. In the later 
stages, then, opportunity for the development of zones of cells free from 
grain substance would have been limited by the closeness together of 
the crystal nuclei. Indeed, samples of this crop have been seen in 
which the grain substance seemed to have been thrown down in prac¬ 
tically every cell, much in the manner of that of flue-cured tobacco, 
though greater in amount. Of interest to note in passing is the fact that 
the burning properties of this crop, much of which is still in storage, are 
very gradually improving. It seems probable that this may be due 
in part to the slow aggregation of grain material rather than to the loss 
through aging of some substance injurious to the burning quality. 
The leaves upon which the observations were made at Red Lion, Pa., 
were sampled after the curing had been completed, and it was found 
that the grain throughout the leaf was in practically the same condition 
