Nov. i, 1920 Composition of Normal and Mottled Citrus Leaves 163 



fruit (Citrus grandis Osbeck) leaves grown in California. Further 

 reference will be made to this paper later. 



As is well known, the composition of annual herbaceous plants depends 

 on their age. It has been shown that the ash content and the proportions 

 of the individual constituents absorbed from the soil change as growth 

 proceeds. Of the changes in perennials much less is known. It seems 

 reasonable to suppose, however, that the growth processes are similar. 

 The periodically developing new shoots may be likened to the portion 

 of annual plants growing above ground. 



New shoots appear on citrus trees several times each year. The tree, 

 being evergreen, bears leaves at all seasons. Consequently, the foliage 

 is composed of leaves of different ages. A given leaf ordinarily remains 

 on the tree for a period of from two to three or more years. 



SELECTION OF SAMPLES 



Special care has been taken to secure representative samples of leaves 

 of known age. Familiarity with the appearance of developing citrus 

 leaves proved to be a material aid in selecting the samples. A consider- 

 able portion of the samples were obtained from trees growing near the 

 laboratory where daily observations were made. The leaves of the 

 Washington Navel and Valencia orange, the Eureka lemon, and the 

 Marsh seedless grapefruit have been analyzed. Each sample was com- 

 posed of several hundred leaves, collected from six or more adjacent 

 trees, all of which were reasonably uniform in appearance and the culture 

 and fertilization of which had been the same. The trees were 10 or more 

 years of age. The entire leaf, including the petiole, was analyzed as a unit. 



The samples were picked from the trees, placed in tight bags and 

 immediately taken to the laboratory and weighed. In most cases this 

 procedure did not require more than 30 minutes. In order to remove 

 dust and other adhering foreign material, the leaves were thoroughly 

 cleaned by wiping each leaf with a moist cloth, but washing with water 

 was necessary with a few samples heavily coated with dust or showing 

 evidences of residues from previous spraying. Early in this work it was 

 found that the samples from which the dust had not been completely 

 removed contained abnormally high percentages of silica, alumina, iron, 

 and inorganic materials not soluble in dilute hydrochloric acid. 



METHODS OF ANALYSIS 



The samples were dried at 105 C. for 24 hours, and the loss in weight 

 was calculated as moisture. The dry samples were ground to a powder in 

 a small hand mill, were thoroughly mixed, and were then stored in 

 tightly stoppered bottles for analysis. 



Total nitrogen was determined by the official Kjeldahl method, modified 

 to include nitrates. Total sulphur was determined by the sodium-peroxid 



