116 BOTANICAL GAZETTE [FEBRUARY 
xanthophyll in green Coleus leaves was about one-third of the 
amount present in most leaves. 
Carotin.—Mottled Coleus leaves were’found to contain about 
0.3575 gm. of carotin per 1000 gm. of fresh leaves, while green 
Coleus leaves had 0.0894 gm. and green lilac leaves had 0.1324 gm. 
None of the leaves analyzed by WILLSTATTER gave as much carotin 
as did the mottled Coleus leaves. Poplar leaves (0.097) had about 
the same amount of carotin in them as did green Coleus leaves, 
while the leaves of Sambucus nigra (0.134) and Fagus silvatica 
(0.131) had about the same amount of carotin in them as did 
lilac leaves. 
The ratio of carotin in lilac leaves was found to be 2 rape 
3 
or 0.48; for green Coleus leaves nian or 1.05; for mottled 
0.0870 
Q. ad 
Coleus leaves — ,or1.49. WILLSTATTER found that the aver- 
age ratio was pe o.1. Even in green Coleus leaves the 
carotin was higher than the average, and the ratio in the mottled 
leaves was greatly increased over what it should be if the leaf 
were normal as to its yellow pigments. 
Discussion of leaf pigments 
Various theories have been proposed to explain how the pigments 
change as the leaf yellows. Swart (48) found that yellowing of 
leaves which are dying begins in that part of the parenchyma which 
is farthest from the vascular bundles, and takes place last in the 
largest vascular bundles. In connection with the disappearance of 
chlorophyll on aging of the leaf SwArt mentioned three possibili- 
ties: the chlorophyll either was transported or it remained in the 
leaf when it broke down, and if it broke down in the leaf the decom- 
position products either were transported to the stem or else 
remained in the leaf. He thought that chlorophyll in the form 
of decomposition products passed from the leaves into the stem, 
while the yellow pigments remained in the leaf. 
3 For comparative work on the yellow pigments Lovibond slides have been found 
to be quite satisfactory. 
