Nov. 6, 1916 
Grain of the Tobacco Leaf 
273 
smoking, they have been considered by many to be composed of potassium 
nitrate. However, it has been shown that the grain is slowly soluble in 
water. This was done by allowing free-hand sections of a fermented leaf 
to remain in water for 4 hours and also by permitting a piece of a similar 
leaf to soak in water on a slide for 17% hours. In order to show the posi¬ 
tion of the grain bodies and the idioblasts containing calcium oxalate, 
camera-lucida sketches were made with the aid of polarized light at the be¬ 
ginning of the treatment with water. In both cases, at the end of 4 and 
17 hours, respectively, no crystalline material remained in the positions 
of the grain bodies, where at the beginning of the experiment the bodies 
were highly active in polarized light. In the positions of the bodies, 
however, both in the sections and in the piece of leaf, the cells that had 
contained the crystalline material were found to be markedly distended, 
although upon the application of the slightest pressure their walls imme¬ 
diately collapsed, giving additional proof that the substances which had 
formerly filled the cells and held them rigid had been dissolved out. The 
calcium oxalate sand crystals and -the scattered, single crystals referred 
to above remained unchanged. 
In a subsequent experiment a piece of fermented leaf tobacco was 
dehydrated in alcohol and cleared and examined in xylol to determine the 
character and distribution of the grain bodies and at the same time the 
position and abundance of the idioblasts and the single, scattered crystals. 
The xylol was then removed from the piece with alcohol and the latter in 
turn displaced by distilled water, in a relatively large volume of which the 
material was allowed to remain for 24 hours at room temperature. An 
examination with polarized light was then made with the specimen 
mounted in water. In this case also it was noted that the crystalline 
material had disappeared from the grain bodies, but it was also evident 
that neither the calcium oxalate sand crystals nor the single, scattered 
crystals had been affected by the treatment. This was verified by 
dehydrating, clearing, and mounting the tissue as already described. 
The piece of leaf was then run back through water and allowed to stand in 
50 per cent acetic acid for 48 hours and mounted and examined in the 
same medium. Both at this examination and after washing in water 
and again dehydrating and clearing, no scattered, single crystals could be 
found—that is to say, the only crystalline material remaining in the 
tissue after successive treatments with distilled water and with 50 per 
cent acetic acid was the sand crystals of calcium oxalate. However, 
these last all disappeared, leaving no optically active crystalline sub¬ 
stance whatever in the cells after the tissue had been subjected to treat¬ 
ment with 50 per cent hydrochloric acid for about 17 hours. 
When separated from the surrounding tissues, however, the grain bodies 
seemed to be less readily soluble in distilled water than when they were 
treated in situ . This is probably due to the presence of some substance 
in the tissues of the leaf which affects the solubility of the grain. In 
