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Orange fruits undergo certain definite and progressive changes in chemical composition during growth and maturation. The rates at which these changes occur depend chieflv upon climatic and soil conditions, but they are also somewhat affected by the rootstock, as shown by HODGSON and EGGERS (15), SINCLAIR and BARTHOLOMEW (17), and others. While studying the influence of rootstocks on the composition of citrus fruits, it seemed important to the authors to investigate the changes that occur in the soluble constituents of the juice during growth and maturity of the fruit, and, especially, to correlate the concentration of one soluble constituent with that of another for the purpose of determining their physiological and biochemical characteristics. The present studies were therefore undertaken.It is well known that differences in the composition of citrus fruits are due not only to variety and similar factors, but also to the influence of the geographical location in which the fruits are grown, and to seasonal changes affecting the rate of the ripening processes. A study of the effects of these environmental factors on the composition and quality of the fruit has clearly demonstrated that, without actual investigation, it is not safe to conclude that the characteristics of the citrus fruits in one locality are the same as those of the fruits in another locality. For this reason it is of extreme importance to know the changes in soluble solids, total and reducing sugars, acids, and pH that occur during the growth and maturity of citrus fruits in the different citrus-growing areas of southern California. A knowledge of the interrelation of these particular constituents has served as a foundation upon which a more extended and specialized program of research on citrus fruits has been initiated.The results reported in the first part of the present paper, which concerns the interrelation of juice constituents, are especially significant because they show the combined effects of different rootstocks, soils, and regional and annual climatic factors on the constituents of orange juice, over a period of several years. Data presented later in the paper show the effect of external factors and of some of the juice constituents on the buffer properties of the juice.

sions have been drawn on scant data. Certain facts have, however, been fairly well established. Hume (24) reported on a Florida experiment in which fruit samples from Rough-lemon stock had a higher acid percentage and a lower sugar percentage than those of the same variety on sour-orange stock. Since these results were published, later investigations (20) in Florida have shown the reverse to be true. In Australia, Quinn (31) has observed that fruit samples from the Washington Navel and the Thompson Navel varieties on sweet-orange rootstock had higher concentrations of sugars and acids than similar fruit produced on Rough-lemon stock. Under California conditions, Hodg-son and Eggers (23) have reported that fruit samples from Valencia orange, Marsh grapefruit, Bearss lime, and Eureka and Lisbon lemons yielded higher soluble solids and acids when on 'I'rifoliate-orange rootstock than when on sourorange, sweet-orange, grapefruit, or Rough-lemon rootstock. Fruits from the Rough-lemon stock had, in every instance, the lowest soluble solids and acids. Similarly, Harding et ale (20), in Florida, found that the concentrations of soluble solids and acids were higher in Valencias grown on sour-orange rootstock than in those grown on Rough lemon. In a report on rootstock experiments in Argentina, Schultz (33) has recorded the total soluble solids, total sugars, and total acids in the j nice of several citrus varieties on various rootstocks. The portion of his data that is of particular interest in the present paper is that concerning the comparative amounts of soluble constituents in the juice of several citrus varieties on sourorange and on Trifoliate-orange stocks. The mean total soluble solids of 10 determinations from seven varieties of citrus on sour-orange stock was 13.38 per cent; the mean total soluble solids for similar determinations from Trifoliate stock was 13.24 per cent. In 8 of the 10 determina.tions, samples from the Trifoliate stock had lower total soluble solids, in 9 less acid, and in 5 slightly higher amounts of total sugars than those from the sour-orange stock. All these investigations, therefore, have served to establish the fact that the rootstock does, in some cases, affect the composition of the fruit. Rough-lemon rootstock appears to be an extreme example: most commercial varieties of citrus on Rough lemon yield fruit of low acid content, with, usually, a low sugar concentration and, consequently, a low concentration of total soluble solids in the juice. The characteristic low acid content of fruits from Roughlemon stock would result in higher ratios of total soluble solids to acids earlier in the season than in fruits from the other stocks.. The present experiments were designed to test these findings for oranges and grapefruit on a large number of rootstocks growing on different soil types and under different climatic conditions in California. The originators of the Station experiment attempted to eliminate as many as possible of the other variable factors inherent in such a problem. On the sampl...

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