A Chemical and Physiological Study of Mottling of Leaves

Abstract

1. The leaves of Coleus Blumei (var. Golden Bedder) are very prone to mottling or loss of chlorophyll. Mottling progresses from the lower leaves upward. Mottling of the leaves takes place first at the edge of the leaf and progresses slowly toward the veins and to the base of the leaf. Usually the pair of leaves immediately above these mottles next, and so on as the plant grows. 2. In mottling the chloroplasts lose their green color, become reduced in size, and carry on very little photosynthesis. 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. 14. Mottling of the leaves greatly lessened the carbohydrate output. 15. The catalase activity of the leaves was very greatly reduced as the leaves mottled. 16. The dry weight of the mottled leaves was less and the ash greater than that of healthy green leaves. 17. In mottled leaves the weight of F1 and of F3 was less, while that of F2 was more than that of the green leaves. 18. Protein nitrogen decreased in all of the three fractions as the leaves mottled, while phosphates decreased in F3, increased in F2, and almost disappeared in F1. 19. The amount of chlorophyll (a and b) was about one-fifth of that of lilac leaves; the proportion of a to b was the same as in other plants (lilac). 20. The carotin and xanthophyll content greatly increased as the leaves mottled. 21. Bacteria were found within the cells of the mottled leaves, but it is not known whether they bear a causal relation to mottling or not.