1921] _ SCHERTZ—MOTTLING 123 
decomposition. It is a great nitrogen user, and it is difficult to 
know what use is made of all the nitrates it consumes. One 
wonders whether there is a denitrifying process going on within the 
leaves which keeps the nitrates more or less depleted, and in case 
of lack of continuous additions completely removes them. This 
or some draft on the nitrogen of the leaf leads to a decomposition 
of nitrogen compounds of the leaf, including proteins, phospho- 
lipines, and chlorophyll, the decomposition of the latter producing 
the mottling. All the experimental evidence points to the shortage 
of nitrogen as the cause of chlorophyll decomposition in the plant 
studied, a plant very prone to mottling. One would hardly 
expect the same limiting factor to determine chlorophyll decom- 
position in plant organs in all cases, but many of the cases of 
chlorophyll loss discussed, whether involving loss from plants 
grown in cultural solutions, or in soils in the midst of the growing 
season, or loss accompanying autumnal coloration, point in the 
same direction. In the Coleus studied it is evident that there is 
little ground for Swart’s view that high acidity of the leaves leads 
to a decomposition of chlorophyll by splitting magnesium out of 
the molecule. Cultures with cuttings of this variety of Coleus 
also show that under ordinary cultural conditions the plant bears 
little margin of phosphate supply, while it bears a great excess of 
calcium, magnesium, and iron. The narrow margin of phosphate 
supply does not manifest itself in mottling, but only in limited 
growth. The narrow margin of nitrogen, on the other hand, mani- 
fests itself both in limited growth and in mottling. If IwANowskKI 
is correct in his assertion that carotin and xanthophyll render 
chlorophyll more nearly light stable, an increase in these pigments 
during mottling may act in a protective way against decomposition 
of chlorophyll. 
From the various investigations presented two things are of 
striking interest: the decomposition of chlorophyll and the great 
amounts of yellow pigments which are present when chlorophyll 
is absent, whether it is in etiolated plants, algae grown in the 
dark, plants which have poor nutrition, or when leaves mottle. 
Since the carotin is present in greater amounts when chlorophyll 
is absent, and since carotin apparently decreases as chlorophyll 
