Nov. 6,1916 
Grain of the Tobacco Leaf 
271 
first type, in that the bodies are usually spherical; but here the surface is 
decidedly nodular and the cells included may be either the palisade or 
the spongy parenchyma, or both. The crystals are radially arranged in 
small groups the individuals of which appear to be thin, narrow plates, 
and the color is more gray than brown (PI. 16, fig. D). 
The fourth type attains the largest size and always has one surface 
in common with the surface of the leaf. The particles consist of a num¬ 
ber of cells, palisade and epidermal, filled with a mass of dark-brown or 
black substance which in the unbroken particle is inactive in polarized 
light. When crushed, however, the fragments between crossed Nicol 
prisms show the presence of crystalline material the form of which is 
not apparent. These dark bodies are very striking, in that the epidermal 
surface is usually craterlike in appearance, having a concavity which 
frequently contains a few minute, colorless crystals surrounded by a 
raised black ring. In a few of this type the central portion of the upper 
surface shows no concavity, but radiating lines extending from a centrally 
located spot beneath which the substance of the particle is soft and 
easily crumbled suggest that this spot marks the location of the base of 
one of the large trichomes or, possibly, the position of a stoma which 
failed to close during the curing process (PI. 16, fig. E). 
The fifth type of grain is composed entirely of microscopic sphere 
crystals which are very active in polarized light and plainly show the four 
extinction bars which rotate upon revolving the analyzer. Unlike the 
other types, they usually do not fill the cells in which they occur. They 
are colorless or light brown in ordinary transmitted light and possess no 
visible differentiation into individual crystals (Pi. 16, fig. F). Tunmann 
(8, p. 147) indicates that these spherites, which he believes to be malic- 
acid salts, separate out when dried tobacco is placed in alcohol. The 
writer has observed that they are formed in the leaf during the process 
of curing and that in some instances they are visible under the micro¬ 
scope in the untreated, dry leaf with the aid of strong polarized light, 
even after fermentation has been completed. 
OTHER CRYSTALLINE MATERIAL OF THE LEAF 
Aside from the grain, two other types of crystalline material are found 
in the tissue of the cured and fermented tobacco leaf. One of these is the 
cryptocrystalline or sand crystals of calcium oxalate contained in certain 
cells (idioblasts) which are always present in all tobacco, even in the 
green leaf while it is still attached to the growing plant, and which show 
no appreciable change during the process of curing or fermentation. The 
other is that which appears in nearly every cell of the leaf in both green 
and cured tobacco and consists of small, single prisms. Some of the 
properties of both of these types will be mentioned in connection with a 
consideration of some of the chemical characteristics of the grain (PI. 
16, fig. A, and PI. 17, fig. A). 
