UNIVERSITY OF CALIFORNIA PUBLICATIONS 



IN 



AGRICULTURAL SCIENCES 



Vol. 3, No. 3, pp. 37-54, plate 12 September 29, 1917 



SOME ABNORMAL WATER RELATIONS IN 

 CITRUS TREES OF THE ARID SOUTH- 

 WEST AND THEIR POSSIBLE 

 SIGNIFICANCE 



BY 



EGBERT W. HODGSON 



INTRODUCTION 



The progress of the development of the citrus industry, in general, 

 and that of California in particular, has frequently been retarded or 

 temporarily stopped by serious obstacles in the form of insect pests 

 or plant diseases. Some of the most baffling of these troubles fall 

 naturally into a group which for want of a better name has come to 

 be known as that of ' ' physiological diseases, ' ' which are thought to be 

 caused by various obscure derangements of nutrition or other vital 

 functions. This group includes mottled-leaf, die-back, chlorosis, June 

 drop, puffing of the fruit, and others of less importance. Knowledge 

 of the true nature of this class of diseases is extremely meager in spite 

 of the fact that they have received much earnest attention from scien- 

 tific investigators ; and little can be accomplished in the way of devis- 

 ing control measures until much more is known in regard to them. 

 Nor can we hope to progress far beyond the realm of speculation with- 

 out greatly augmenting our knowledge of the physiology and anatomy 

 of the normal citrus tree when grown under any one of a series of 

 very widely varying environmental complexes which obtain in differ- 

 ent parts of the arid southwest. 



It is, therefore, proposed to attempt by means of a series of sys- 

 tematic experimental studies to obtain some definite and accurate 

 information on the physiology of the genus Citrus. It is hoped that 

 the results may serve as a basis for the elucidation of some, at least, 



