1917] Hodgson: Abnormal Water 'Relations in Citrus Trees 5] 



as compared with the leaves and, moreover, it is highly probable thai 

 a large percentage of this area is non-functional, being obstructed 

 by accumulations of a resinous nature, there is small likelihood for 

 absolute loss of water in this manner to the extent noted. Hence 

 there seems but one way to explain it and thai is by movement back 

 from the fruits. 



Evidence of an indirect nature pointing to the same conclusion 

 lies in the fact that there are some indications thai abscission of ;i 

 certain proportion of the young fruits is directly due to the influence 

 of hydrolysing enzymes secreted by certain saprophytic or facultative 

 parasitic fungi always found present on the shriveled style and fre- 

 quently in the proliferations of the navel. Such enzymes in order to 

 act on the abscission layer must be drawn back through the vascular 

 systems of the fruit into the pedicel where this layer is located. 

 Investigations on this point are now in progress. 



Experiment 7 — Three similar fruits were selected on different 

 parts of a tree ; on one of the lower branches in the shade, at a height 

 of four feet, and in the top of the tree in full sunlight. At noon each 

 fruit was pared so as to admit entrance of a solution and then plunged 

 quickly into a small vial containing a watery solution of eosin. These 

 vials were securely tied to the shoot and left suspended for two hours. 

 At the end of that time, on cutting leaves from these shoots, eosin 

 staining was found in the vascular systems of all. On examining back- 

 ward toward the tree, eosin was found as far back as thirty centi- 

 meters. This experiment was repeated a number of times both at 

 Edison and at Riverside and uniformly gave the same results, although 

 much less marked at the latter place. In every case the backward 

 movement of the eosin solution was at its maximum during the 

 afternoon. 



Cutting the ends of branches in situ under a watery solution of 

 eosin was tried at different times of day and gave similar results. 

 This experiment was performed at Edison, Riverside and [ndio. At 

 the latter place, with the temperature at 116° F and the humidity at 

 8% the eosin solution traveled backward at the astonishing rate of 

 30 cm. per minute at 6 p.m. Similar results were obtained using 

 Eucalyptus rudis as material. In fact with long slender poles of 

 Eucalyptus tereticornis at Edison, such a remarkably rapid backward 

 flow of eosin was observed (105cm. in one minute) in the afternoon 

 as to compel the conclusion that after all, the force responsible for 

 this movement under such conditions must be negative pressure pro- 



