192] © SCHERTZ—MOTTLING 83 
healthy green leaves. Leaves in the medium stage of mottling 
sometimes contained more and sometimes less of these four elements. 
Midribs of the healthy leaves contained less of these elements 
than the mesophyll, while in badly mottled leaves the midribs 
contained more calcium and more phosphorus. The petioles 
contained less iron, calcium, and magnesium than either midrib or 
mesophyll in healthy and mottled leaves, while in badly mottled 
leaves the petioles contained more iron, calcium, and magnesium 
than either the midrib or mesophyll. Old leaves were found to 
contain more calcium and magnesium than new leaves. The 
yellow spots in the mottled leaves contained less calcium, mag- 
nesium, and phosphorus than the green parts of the same leaf. 
In working on the golden privet JENSEN found that the yellowed 
leaves contained more iron and 2.5 times as much phosphorus as 
the green ones. The increased amount of iron, calcium, magnesium, 
and phosphorus in the conducting tissues of the badly mottled 
leaves indicated that there was difficulty in the transfer of these 
materials to and fro. 
McBeErH (37) found that plots receiving large applications of 
commercial fertilizers generally bore trees with badly mottled 
leaves, while trees receiving no nitrogen or barnyard manure 
generally showed little mottling. In other groves extreme mottling 
was frequently associated with a high nitrogen content. Moisture 
and nitrogen content of the mottled leaves were found to be higher 
than in the normal green leaves. His work seemed to indicate 
that too much nitrogen caused the mottling of citrus trees. 
Investigation 
The mottling of Coleus leaves occurs in a regular manner, pro. 
ceeding from the edge inward and toward the base of the leaf. The 
edge usually yellows first, while only in rare cases do yellow spots 
develop in the central part before the edges become yellow. The 
basal portion seems to retain its green color longer than the tip, 
and the veins or the region near the veins are the last to lose their 
green color. The leaves on plants in good soil often die at the tip 
about the time of mottling, while the leaves on plants in poor soil 
rarely show this characteristic. Usually the leaves from plants 
