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



DISCUSSION OF RESULTS. 



VARIABILITY IN CITRUS FRUITS. 



Certain differences in the data reported exist. It is necessary to 

 ascertain whether these differences in composition are inherent in 

 the fruits of individual trees or whether they extend beyond the indi- 

 vidual tree and constitute a difference between strains. 



Citrus fruits are variable in composition, and the time of year in 

 which lemons mature has a bearing upon their composition (})■. In 

 comparing the composition of fruit from different trees, therefore, it 

 is impossible accurately to compare samples from two trees unless the 

 fruit was gathered at approximately the same time. This does not 

 mean that the samples must be picked the same day, or even perhaps 

 the same week, but they should be picked in the same month. Cer- 

 tainly samples gathered during different seasons of the year are not 

 comparable. Such precautions become unnecessary only when the 

 number of samples is so great as to preclude the probability of error 

 from seasonal variations in composition. Therefore the comparisons 

 obtained in the later experiments are between lots of fruit gathered at 

 approximately the same time. 



In order to determine the significance of any difference, not only 

 the variation in composition between samples of fruit from the same 

 tree, but also the variation in composition existing between samples 

 of fruit from different trees of the same strain must be carefully 

 observed. Only in cases where the difference as a whole between 

 strains is greater than that between trees of the same strain can it 

 be safely assumed that a significant difference exists. 



DIFFERENCES IN COMPOSITION OF FRUIT FROM THE SAME TREE AND FROM TREES 



OF THE SAME STRAIN. 



The variability in fruit from the same tree is shown best by the 

 probable errors given with each determination in Tables 3 and 4. 



As the number of subsamples making up each sample to some 

 extent affects the probable error, unusually lar^e errors were some- 

 times due to the small number of subsamples taken. The difference 

 in composition of samples from the same tree gathered at different 

 times also varies. Notwithstanding these facts, it seems that, as a 

 whole, where 25 or more fruits constitute a sample, different trees 

 show approximately equal probable errors. 



The variation in specific gravity of Eureka lemons, as shown by the 

 probable error, is from 0.001 to 0.008, being in most cases from 

 0.002 to 0.003. Only 3 of the 77 samples reported in Table 3 show 

 probable errors in specific gravity greater than 0.004. Naturally 

 the variation in rind is greater than that in either specific gravity or 

 acidity of the juice. This is due in part to the nature of the fruit 

 and in part to the accuracy with which the analytical determinations 

 can be made. The probable errors in this determination vary from 

 0.1 to 1.5, with an average error of approximately 0.6. Eight samples 

 have errors of 1 or more, but 6 of the 8 samples consisted of 15 fruits 

 or fewer. The samples are rather uniform in acidity, the probable 

 errors ranging from 0.01 to 0.12, the average being close to 0.05. 



The variation in the specific gravity of Lisbon lemons is from 0.001 

 to 0.005, with an average midway between these limits. The prob- 

 able errors for the rind vary from 0.1 to 1.5, with an average of 



