CRITERIA AND METHODS 129 



above the ring had increased considerably in diameter with 

 a corresponding increase in conductive capacity. This 

 even exceeded that of the lower part of the stem which, in 

 the normal stems, has the highest conductance of the three 

 parts. One would hardly be justified in explaining the 

 change in relative rates of flow between upper and middle 

 parts as due to the plugging of the middle part by a ring, 

 when it is obvious that the change is due to increased con- 

 ductance of the upper part and not to a decreased conduct- 

 ance of the middle part. Although the wounds presumably 

 were not protected, the increased resistance was very 

 slight at best. 



Maskell and Mason (1929a) also mention an increased 

 resistance to water flow resulting from ringing and they 

 state that it becomes evident about 14 hr. after ringing, 

 but they imply that a failure of the leaves of ringed plants 

 to maintain a normal moisture content is due to an inter- 

 ference in water transport; whereas a change in moisture 

 content is certain to result from a failure to transport 

 solids from the leaf and there may be not the slightest 

 interference in water flow. Furthermore they used vaselin 

 as a protective agent which I have found to be injurious to 

 twigs, and it has not been demonstrated to be harmless as 

 a ring wound dressing. 



Even if further investigations demonstrate conclusively 

 that partial plugging invariably results from ringing, the 

 effect is at most slight when the ring wound is protected, 

 and especially so when compared to deep notching or the 

 cutting of one-half to three-fourths of the xylem, and yet 

 when the xylem is injured by such cutting, there seems to 

 be a relatively slight effect on transport. When, on the 

 other hand, the phloem is completely cut, the transport 

 is significantly reduced. Evidence from most of the types 

 of ringing experiments here reported clearly demonstrates 

 that a narrow bridge of phloem is adequate for almost 

 normal food transport. And since with complete ringing 

 but a part of the xylem at most can be plugged, because 

 the parts above show no signs of water deficit, it seems 



