ON DROSERA ROTUNDIFOLIA 3 
3. PIGMENT 
The red pigment of Drosera occurs predominantly in the leaves 
and the root-cap. Young leaves frequently have the pigment 
restricted to the glands of the tentacles. Later it appears in the 
epidermal cells of the marginal pedicels. Leaves of old plants 
often have the entire leaf-blade pigmented and, as the leaf 
matures, the color spreads down the petiole and often into the 
stalk. In general young plants are much greener than old ones, 
but wide variations are found. 
The red pigment of Drosera rotundifolia and D. longifolia is 
identical with one of the pigments which Rennie (’87, ’93) extracted 
from rhizomes of D. Whittakert. Its formula is CyHsO;, and it 
is probably trihyd thylnaptl i , since it gives the 
reaction of Hrissbineret ani eaibes (07) characteristic of 
a-napthoquinones. 
To obtain the pigment, place a deep red leaf on a slide, add a 
few drops of hot alcohol, put on a cover-glass and heat directly 
over boiling water. The pigment is extracted from the leaf and, 
on the evaporation of the alcohol, it is deposited around the edges 
of the cover-glass. It forms crystals which are small red disks. 
It is insoluble in cold water, hardly soluble in cold alcohol and 
glacial acetic acid, but dissolves readily in boiling water, hot 
alcohol and ether, and to a lesser extent in benzol and carbon 
disulphide. It is soluble in alkalis. When a leaf is treated with 
ammonia, the pigment turns dark violet or brown; on standing 
the color fades. A timely treatment with dilute acid precipitates 
the pigment and restores the red color, but this does not occur 
after prolonged action of the ammonia. Reduction with stannous 
chloride and alcoholic hydrochloric acid gives a yellow product 
which crystallizes in needles. This is reoxidized to the original 
compound, when allowed to stand in alcoholic or alkaline solution 
exposed to the air. These properties were found for the pigment 
of D. rotundifolia. They coincide with those given by Rennie 
for the compound CyHsO;, and confirm the suggestion of their 
identity put forward by Kraemer (’10, p. 285). 
Experiments were made with the green plants to determine 
under what circumstances the pigment reappeared. Several 
plants of D. longifolia were cultivated for a month in a moist 
