40 University of California Publications in Agricultural Sciences [Vol.3 



diurnal condition of dessication has been found by Livingston and 

 Brown to serve as a check on the absolute transpiration and has been 

 termed "incipient drying." Lloyd 5 independently obtained similar 

 results in his investigations on Fouquieria splendens and Mrs. Shreve 6 

 established the same phenomonon in 1913 with Parkinsonia micro- 

 phylla. 



Inasmuch as the genus Citrus is undoubtedly a mesophyte of 

 tropical origin and therefore grown in the interior valleys of Cali- 

 fornia under purely artificial conditions, 7 it would naturally be 

 expected that the abnormal water relations above discussed might 

 obtain to an unusual degree, especially during the hot growing period, 

 when the ability of the plant to make up for excessive transpiration 

 is taxed to the limit. Citrus fruits are borne on wood of the current 

 season's growth which ordinarily bears six to eight leaves on the same 

 fruiting shoot. Therefore, it seemed reasonable that under conditions 

 of excessive transpiration the leaves might draw on the water supply 

 of the fruits and thus bring about an abnormal water relation. With 

 the above considerations in mind it occurred to the writer that this 

 premature fall of the fruits might be due to irregularities or abnormal- 

 ities in the water relations between the fruits and foliage, resulting in 

 abscission in some way analagous to the shedding of cotton bolls under 

 the stimulus of a water deficit. 



The method used in obtaining the data here presented consisted 

 in the main of simple moisture determinations of leaves and fruits of 

 various kinds taken at different hours of the day. The material was 

 gathered and quickly placed in weighing cups fitted with ground 

 glass covers. After weighing, the material was thoroughly dried 

 and then reweighed. For convenience in the case of fruits and large 

 leaves, the material was cut into small pieces. The calculations are 

 based on the dry weight of the material, except as otherwise stated. 

 The data obtained are shown in condensed form in table 1. The 

 figures shown represent averages of at least ten duplicate determina- 

 tions, and in most instances of more. 



The data presented in table 1 show some very interesting condi- 

 tions. It is quite clear that, with the exception of the new succulent 

 growth, the young fruits are at all times higher in water content than 

 the leaves situated near them. These data also seem to leave no doubt 



s Plant World, vol. 15, p. 11, 1912. 



6 Ann. Rpt. Dir. Bot. Res. C. I. W., Feb. 12, 1913, p, 81. 



7 For a more complete discussion see Livingston, B. E., "A single index to 

 represent both moisture and temperature conditions as related to plants." 

 Physiological Researches, vol. I, No. 9, April, 1916. 



