4 BULLETIN 1255, U. S. DEPARTMENT OF AGRICULTURE. 



or not the element would vary, and whether or not the variation was 

 sufficient to be commercially important. The object being to dis- 

 cover chemical or physical differences existing between strains of 

 fruit of the same variety, the outstanding characteristics were chosen 

 for observation. Whenever possible, characteristics had been studied 

 in the field by A. D. Shamel and his associates (5, 6), so that the data 

 here reported are the results of laboratory work alone. Thus, the 

 tree characteristics and the yield, color, shape, and size of fruit, and 

 its seed content, were determined in the field; while specific gravity 

 of the fruit, percentage of rind, oil, pulp, and juice, and percentage 

 of acid and sugar in the juice, were determined in the laboratory. 

 In the second phase of the work, the determinations were confined 

 to specific gravity of the fruit, percentage of peel, and percentage of 

 acid in the juice. 



Specific gravity is of value in judging the quality of citrus fruit. 

 First, and probably of greatest importance, is the compactness of the 

 fruit. Puffy, coarse- textured, hollow-centered fruit has a low specific 

 gravity. As the juice constitutes nearly two-thirds of citrus fruit 

 by weight, the specific gravity of the juice, to that extent, determines 

 the specific gravity of the fruit. For this reason, considering oranges 

 of equal size, the heaviest ones are usually the sweetest. The texture 

 of the rind perhaps plays but a small part in determining the specific 

 gravity. Coarse rind, however, is usually accompanied by coarse 

 rag and flesh and hollow centers. 



The oil content of citrus fruit is of importance only in so far as 

 oil is a by-product of the citrus industry. Other factors being equal, 

 however, the fruit producing oil in greatest quantity and of highest 

 quality is of most value. Oil occurs in comparatively small quan- 

 tities and a decided variation in the content is necessary to appre- 

 ciably affect the value of the fruit. 



Rind, pulp, and juice, of course, are primary factors in judging the 

 quality of citrus fruits. A fruit with a thin rind may not ship as 

 well as one with a thicker and tougher covering, but the consumer will 

 choose the former where opportunity offers. 



Insoluble solids in the pulp indicate its texture, coarse, tough pulp 

 having a high content of insoluble solids. Cell and partition walls 

 are included in the material measured by this determination. 



Sugar, of prime importance in oranges and grapefruit, is of little 

 value in lemons. There seems to be some difference, however, in the 

 quantity contained in lemons of different strains. 



Acid is of great importance in all classes of citrus fruit. In oranges 

 and grapefruit it is an indication of immaturity; in lemons it is the 

 valuable constituent of the juice, both when the fruit is sold fresh 

 and when it is used for the manufacture of citric acid. 



METHODS OF ANALYSIS. 



The methods of the Association of Official Agricultural Chemists 

 were used in making the determinations, wherever such methods 

 existed. Otherwise, others of recognized accuracy were employed. 



Specific gravity of the fruit was determined by weighing it first 

 in air and then under water. No difficulty was experienced with 

 air bubbles clinging to the fruit. 



The volatile oil in the peel was determined by the method of Wilson 

 and Young (#), using the whole fruit finely ground. No method lias 



