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volatile oils of different Monardas and found crystalline deposits 
in the oils after standing. Careful work upon authentic material 
was not done until begun under the direction of Professor Kremers 
at Madison. Numerous investigations have been made there, 
especially upon the essential oils of this group. The oils of 
Monarda citriodora, M. didyma, M. fistulosa and M. punctata 
were studied in detail. With the exception of M. didyma the 
oils all contained considerable amounts of aromatic phenols. 
Hydrocarbons like limonene were also present in several species. 
As a rule, all of the oils were light in color when freshlv distilled 
but gradually turned darker in the course of time, probably 
owing to oxidation. This led the investigators to look for easily 
oxidizable substances and their search was successful, for they 
found that thymoquinone and certain of its derivatives were 
present in the oils. Now, the quinones, as a class, are often 
colored or yield brightly colored red, orange, or yellow substances 
after chemical treatment. We have here a group of closely 
related plants that contain substances of similar structure from 
the chemical point of view. A study of the part these substances 
play in the pigmentation of the plant was then undertaken. 
The pigments of the different Monardas give to their flowers 
the red, yellow, brown and purple colors that make them attrac- 
tive. These pigments are extracted with various solvents. 
The colors of each are different, but upon chemical study they 
all appear to be derived from one or two closely related mother- 
substances, among which thymoquinone has been obtained in 
the form of beautiful yellow crystals. Substances of this type 
give brilliantly colored final or intermediate oxidation products. 
It was found that the Monardas contain oxidases or oxidizing 
ferments (destroyed by heat) that can oxidize these color-pro- 
ducers from one stage to another with accompanying change of 
hue. Many investigators consider that numerous other cases 
of pigment formation in plants are due to the action of these 
oxidases upon various colorless constituents of the plant. The 
question of pigment production is one of growing interest among 
both botanists and chemists. The present publication is a 
valuable contribution to our understanding of this problem. 
