CAROTINOIDS IN THE PHANEROGAMS 53 



during the greening of etiolated sprouted oats. Inasmuch, however, 

 as he used a eolorimetric comparison of the total alcoholic extract of 

 the etiolated plant with the alcoholic xanthophyll layer of the extract 

 from the green plant following the Kraus separation, it is not dif- 

 ficult to account for his results. Arnaud's (1889) quantitative eolori- 

 metric comparison of the carotin content of etiolated and green leaves 

 of the kidney bean, referred to above, led to completely opposite 

 results. Arnaud's data (calculated from his eolorimetric reading) 

 show 34.0 mg. carotin in 100 grams of the dry etiolated leaves, and 

 178.8 mg. in the same amount of dry green leaves, a result which 

 appears to have been substantiated by the observation of Schunck on 

 etiolated and green daffodil leaves. Kohl (1902f) studied the same 

 question and drew the same conclusion as did Arnaud, namely, that 

 carotin increases during greening. His method of analysis, however, 

 does not permit so exact an interpretation, for he merely compared 

 colorimetrically the total unsaponifiablc pigment extracted from the 

 leaves by alcohol. Kohl's carotin solutions were thus a mixture of 

 carotin and xanthophylls. It is not possible to decide from these 

 observations whether xanthophylls as well as carotin increase in the 

 etiolated leaf during greening. This appears to be the case, however, 

 in view of Ewart's (1918) statement, quoted above, and the fact that 

 xanthophylls are the predominating carotinoids in green leaves as 

 found by Willstatter and Stoll (1913) and Miss Goerrig (1917). 



An interesting phase of the etiolated leaf pigmentation is that of the 

 most favorable conditions for the development of the carotinoids. 

 Light and temperature are obviously the controlling factors. Wiesner 

 (1877b) observed that potato sprouts, which formed in the light, 

 showed little if any yellow pigment, while those which formed in the 

 dark developed from 30 to 150 per cent more pigment. More interest- 

 ing is the result of Elfving (1882), which was confirmed by Immen- 

 dorff (1889), that carotinoids increased greatly in leaves under con- 

 ditions which depressed chlorophyll formation, i.e., low temperatures 

 (2 to 8 C.) and very diffused light. 



Carotinoids in Naturally Yellow Leaves 



Plastids which fail to develop chlorophyll but in which other pig- 

 ments form instead arc called chromoplastids. The pigments of 

 chromoplastids are usually granular, sometimes crystalline and almost 

 invariably yellow to red in color. In the case of some plants the leaf 



