1921] SCHERTZ—MOTTLING 127 
3. In the usual greenhouse cultural conditions, this plant has 
within it phosphorus and nitrogen little in excess of its immediate 
needs. This was shown by cuttings grown in phosphate-free 
nutrient mixtures; failure to grow was noticeable, although the 
plant maintained a healthy green color. When the plants were 
transferred to nitrate-free mixtures, they failed to grow and also 
lost their natural green color. 
4. Under usual cultural conditions these plants seemed to have 
within their tissue magnesium, calcium, and iron greatly in excess 
of their immediate needs. Cuttings grown in nutrient mixtures 
lacking any one of these elements grew and maintained their 
normal green quite as well as in the complete nutrient mixtures. 
5. A deficiency of magnesium or calcium apparently has nothing 
to do with mottling. 
6. More iron was found in all parts of the mottled than in the 
green leaf. 
7. A deficiency in phosphorus caused a larger percentage of the 
leaves to drop than did a deficiency in iron, magnesium, calcium, 
or nitrate. 
8. A deficiency in phosphorus caused more of the leaves to drop, 
while a surplus of phosphorus did not prevent them from falling if 
nitrogen was deficient. 
9. The effect of adding nitrogen to a plant or withholding it 
was shown in a very few days by the change in color of the leaves. 
10. Addition of a nitrogen compound (sodium nitrate) to a 
plant potted in soil kept the leaves on and the plant green, while 
the addition of iron, magnesium, calcium, or phosphate made very 
little change in the appearance of the plant. 
11. In order to maintain a healthy condition and a green color 
the plants seemed to require more nitrate than other plants of 
which we have a record. 
12. The mottled leaves always had a lower percentage of nitrate 
nitrogen, protein nitrogen, ammonium salts, and albuminoid 
ammonia than did the green leaves; mottled leaves had nitrites 
and free ammonia present in them. 
13. The general appearance of the mottling was the same as_ 
that of the leaf of citrus fruit trees. 
