1917] Hodgson: Abnormal Water Relations in Citrus Trees 53 



Conclusion 



This paper deals with one phase of an investigation of a so-called 

 physiological disease, June drop of the Washington Navel orange. 

 An excessive dropping of the young fruits has been experienced for 

 years in the dry interior valleys of California and Arizona. 



An abnormal water relation is found to obtain periodically in 

 citrus foliage and in the young fruits during the hot growing season 

 in these regions. A diurnal decrease in water content of the fruits 

 occurs during the afternoon and is accompanied by a considerable 

 increase in the water deficit of the leaves. Negative pressures of con- 

 siderable magnitude are found in the water columns of citrus trees 

 under these climatic conditions. These attain their maximum during 

 the afternoon. The dropping of the fruits appears to be most severe 

 where the above mentioned water relations are most abnormal. 



Inasmuch as in the case of certain other plants the abscission of 

 young fruits has been shown to be due to abnormal water relations it 

 is suggested that such may be the case here. 



In conclusion, the writer wishes to acknowledge his indebtedness 

 to Professor J. Eliot Coit, under whose supervision and with whose 

 assistance a large part of the experimental work was done ; also his 

 obligations to Professor Charles B. Lipman for his kindly interest in 

 the investigation and for his many useful suggestions, and to the 

 Edison Land and Water Company for their kind and courteous 

 cooperation. 



