126 TRANSLOCATION IN PLANTS 



become evident, for both stems were in competition one 

 with the other. When a defoUated shoot is isolated by a 

 ring, its higher water content, when compared with a 

 similar defoliated shoot not isolated by a ring, is also an 

 indication that the xylem has not been plugged and that 

 water has moved readily. A dye injected into the xylem 

 below such a ring is readily carried past the ring (Curtis, 

 1925). 



Gardner (1925) states that the xylem is unavoidably 

 injured when a ring is made. In order to escape the injury 

 attendant on ordinary ringing, he scraped away the cortex 

 and applied a 7 per cent solution of potassium hydroxide, 

 which was supposed to kill all the tissues external to and 

 including the cambium, but no others. Though he con- 

 siders this method superior to other methods of ringing, 

 the reasons for its supposed superiority are not evident. 

 It may be true that he found less injury than when a ring 

 was carelessly made by a knife and left entirely unpro- 

 tected, but there is certainly no necessity for causing the 

 knife edge to penetrate the xylem at all, and a coating of 

 warm paraffin wax would have prevented other injury. 

 It is rather difficult to conceive of the possibility of apply- 

 ing strong potassium hydroxide or any other soluble 

 material to the outside of a tissue and insure its penetra- 

 tion in sufficient quantities to kill the cambium without 

 penetrating any farther. Furthermore, after the outer 

 tissues are killed, though they may act as a partly protect- 

 ing layer, they probably do not protect the xylem from 

 loss of water as effectively as does paraffin. The fact that 

 the cambium will become active and regenerate new tissues 

 when the phloem and bark are removed over an area 

 several centimeters in diameter, if it had been immediately 

 coated with warm paraffin, is proof that loss of water has 

 not been excessive and that the heat of the paraffin was not 

 too great. 



Swarbrick (1927) also claims that ringing inevitably 

 injures the outer layers of xylem. The injury, however, is 

 undoubtedly due to carelessness and can be entirely 



