142 CALIFORNIA FRUITS I HOW TO GROW THEM 



parison, and to prevent the washing of fertilizers from one fertilized 

 plot to another, but they must also be compared, first of all, among 

 themselves, to determine what is the normal product of the unfertilized 

 land. It will frequently be found that these unfertilized check 

 plots differ more widely between themselves than do the fertilized 

 ones from them or from each other. Systematic experimentation, 

 on plots arranged to avoid such errors, has been continued for several 

 years by the University Experiment Station in the citrus district of 

 Southern California. Results from this work, not yet available, can 

 be secured, when ready, by correspondence with the Station at Berkeley. 

 It is also hoped by this work to secure some knowledge of what specific 

 effects on growth or fruiting are caused by the use of particular sub- 

 stances. Statements now freely made along this line are largely 

 conjectural. 



From these statements it must appear that the prescription of 

 fertilizers is not an easy matter. Disappointments will naturally be 

 encountered, but unquestionably the advantage is on the side of patient 

 trial and wise investment in fertilizers honestly made and honestly 

 sold. The observing grower must learn all that he can from experience. 

 It is obviously the duty of the grower to constantly study fertilizer 

 questions as presented in books and journals and to be alert for obser- 

 vation of the behavior of his own trees with the applications he may 

 make. The publications of responsible fertilizer manufacturers and 

 dealers, also convey important information when read discriminately. 



Though the deficiencies of the soil, as learned by analysis, or by 

 practical test, must be the basis of prescription of fertilizers, the 

 analyses of fruits, as showing the special needs of the plants, are of 

 the highest importance. The following analyses of the different fruits, 

 containing in each case, skin, pulp, and seeds, are almost entirely from 

 California-grown specimens, and are supposed to represent an average 

 composition of the fruits named. 



Quantities of soil ingredients withdrawn by various fruits 



Compiled from analyses by G. E. Colby, University of California. 



t Including hulls. * Estimated. 



