Nov. i, 1920 Composition of Normal and Mottled Citrus Leaves 169 



COMPOSITION OF ORANGE LEAVES AT DIFFERENT STAGES OF GROWTH 



The results obtained from the analysis of samples of leaves approxi- 

 mately one month of age, gathered on May 11, 1917, were found to be 

 considerably different from previous analyses of mature leaves. Samples 

 representing the new spring growth and that of the previous year, gathered 

 from the same trees on May 21, 191 7, also proved to be widely different 

 in composition. These results, together with the discordance between 

 the analyses previously made in this laboratory and those published by 

 Blair (2) from Florida and by Jensen (7) from California, suggested the 

 desirability of making a study on the composition of orange leaves at 

 different stages of growth. 



Samples were collected at four different intervals in the growth cycle. 

 The first represented leaves approximately 1 week old; the second, those 

 6 to 8 weeks old; the third, leaves at full maturity, the ages of which 

 ranged from 6 months to approximately 2 years; the fourth, old leaves 

 that were about to be shed, as indicated by their yellowish brown color. 

 Each sample was picked from six normal, vigorously growing trees of 

 plot V at the Citrus Experiment Station, Riverside, Calif. The samples 

 representing different ages were all taken from the same trees, and those 

 representing the first three periods of growth were gathered on the same 

 day, November 9, 1917. These trees support an abundant foliage; and, 

 as frequently occurs, they at that time bore numerous shoots of varying 

 ages, ranging from a few days to 2 or more years of age, which made it 

 possible to secure samples of widely different ages on a given day. The 

 samples of old leaves were gathered December 10, 1917. 



The data expressed as percentages of the ash show that notable 

 changes take place in the relations of certain constituents as growth 

 proceeds. Especially prominent among these changes are the decreases 

 in the percentages of phosphate and potassium, on the one hand, and the 

 increases in calcium on the other. For example, the ash of navel 

 leaves at the age of 1 week was found to contain 16.83 P er cen t phosphate 

 (P0 4 ), at 6 weeks 7.10 per cent, at maturity 2.47 per cent, while the ash of 

 old leaves contained only 1.32 per cent. 



The changes in the percentages of potassium were quite parallel to 

 those of phosphate. When navel leaves were 1 week of age, the ash 

 contained 19.87 per cent potassium, when 6 weeks of age, 10.32 per cent, 

 when mature, 5.68 per cent, while the old leaves contained only 1.66 

 per cent. 



The percentages of calcium underwent changes quite opposite to those 

 of potassium. With the ash containing 20.72 per cent calcium when 

 the leaves were 1 week old there was an increase to 28.44 P er cen t 

 at 6 weeks, to 33.21 per cent at maturity, and finally to 34.41 per cent 

 in the very old stage. 



