128 TRANSLOCATION IN PLANTS 



both in his own experiments and mine, as due to this dry- 

 ing. He failed to recognize, however, that as all the ring 

 wounds were protected from such loss in the experiments 

 I reported, the water loss was not a factor, and yet the 

 behavior under similar types of ringing was similar. 



It is surprising how frequently possible injury to the 

 xylem is called upon to explain the effects of ringing on 

 transport. Yet one-fourth to one-half or even three- 

 fourths of the xylem may be completely severed without 

 any appreciable alteration in the behavior or composition 

 of the tissues above, if a small part of the phloem also 

 remains. When proper precautions are used, I have found 

 that the resistance to flow of water past a ring is not 

 measurably altered. Gardner (1925) says, "Ringing evi- 

 dently decreases the conducting capacity of stems in some 

 cases as much as 45 per cent," while "The bent section 

 shows no tendency to obstruct the passage of water." 

 But such effects are not evident from his data. As a 

 measure of the resistance he determined the time necessary 

 to force 2 cc. of water through the stem under a head of 

 4}^ ft. of water. He gives such measurements for flow 

 through pieces of equal length (usually 12 cm.) from upper, 

 middle, and lower parts of the stems of the pear. This 

 was done for normal stems, ringed stems, and bent stems. 

 For ringed and bent stems, the rings or bends were located 

 in the middle portion. The average time of five stems for 

 flow in the middle section of normal shoots was 9.95 min. 

 and for the lower portion 8.74, a ratio of 1.14 to 1. For 

 the eight bent shoots the times were, respectively, 6.8 and 

 5.1, a ratio of 1.34 to 1. In the ten ringed stems the times 

 were, respectively, 11.25 and 7.19, a ratio of 1.57 to 1. He 

 says half of the ringed stems had healed over completely. 

 Leaving the five stems out and averaging only the five 

 that did not heal over, the average times were 10.9 and 

 7.8, a ratio of 1.40 to 1, a figure very like those of the normal 

 or bent stems. Gardner evidently compared the resistance 

 of the middle portion to that of the part above the ring 

 but this is not a safe comparison for, as he says, the part 



