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. Whittakeri. Its formula is CnHgOs, and it 

 is probably trihydroxymethylnapthoquinone, since it gives the 

 reaction of Brissemoret and Combes ('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 CnHgOs, 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 



