Al 
venic character, are, of course, produced in the plasmatic parts, but 
secreted rapidly into the cell sap. When the cells die the soluble sub- 
stances locally separated in the cytoplasm and the cell sap intimately 
mix, sincethe coagulating protoplasm, becoming easily permeable, can no 
longer retain any soluble matters—as, for example, oxidase. Thus after 
death the direct action of the oxidase on the oxidizable matter of the cell 
sap sets in with a production of colored bodies, as is the casein the tobacco 
leaves. This action can also be noticed very well in the juice pressed 
out from the fresh leaves, since this juice, containing cell sap as well 
as soluble matters previously contained in the protoplasm, turns brown 
rapidly on coming into contact with air. The darkening of the juices 
of potatoes, beets, and other plants depends upon the same principle. 
CHROMOGENS OF TOBACCO. 
The nature of the chromogenic compounds has not yet been fully 
revealed. It was pointed out in Report No. 59, p. 12, that several dif- 
ferent compounds have to be assumed as contributing to the color in 
the tobacco leaf, and that tannin as well as nicotine contribute only a 
partof it. It is true that the darker tobaccos are generally considered 
aS being the stronger—that is, contain the most nicotine—but, on the 
other hand, it has to be kept in mind that the veins, which contain less 
nicotine than the lamina, are generally much darker colored, a fact hardly 
to be explained merely by the thicker layer of cells. The fact, how- 
ever, that the juice of the lamina turns dark more quickly and intensely 
than the juice of the rib makes it probable that the chromogen of the 
ribs is not easily soluble and differs from that of the lamina. In the 
lamina it is the mesophyll and not the epidermis that contains the chief 
quantity of the chromogen. 
The main chromogens of the leaves are insoluble in alcohol, as is the 
brown product itself. <A piece of young, green tobacco leaf was left in 
alcohol for one day, the chlorophyll being extracted and the leaf 
becoming almost colorless. Upon moistening with water it turned 
brown within two days, the color being darkest in the ribs and veins. 
The main chromogen, therefore, had not been removed by the alcohol 
treatment. 
There is but very little chromogen in the pith, since it becomes only 
slightly brown after several days’ exposure to the air; equally little is 
contained in the vascular bundles of the stalks, except in the youngest 
part. ‘The study of the nature of the chromogens encounters consider- 
able difficulties.! 
1 After this was written, an articie of Behrens appeared in the Landw. Vers. 
Stat., vol. 52, in which he discusses the production of the color. He thinks that 
the brown substance is formed from a chromogen which is split off from a glucosid, 
and that this glucosid is formed during the first or starvation period of the leaves 
in the barn. This opinion can hardly be accepted when we observe the rapidity 
with which the juice of the fresh leaves turns brown upon exposure to the air, 
showing that the chromogen, or rather the ‘‘ soluble” chromogen, is already present 
in the normal leaf. 
