July, 1923] CURTIS — EFFECT OF RINGING A STEM 381 
Furthermore, even though transpiration above a ring may have been 
reduced, the high carbohydrate content of the tissues above the ring, as 
well as the ring itself, would tend to prevent the removal of nutrients once 
they got up past the ring. This failure in removal would tend to offset 
any possible slower absorption that might result from decreased trans¬ 
piration. 
Aside from difficulties in interpretation, resulting from possible differ¬ 
ences in transpiration, there is the difficulty that the xylem itself may 
have been altered by the ringing. Several writers (Daniel, 1906; Combes, 
1912; Higgins, 1919, and others) have offered evidence that tyloses or gum 
may plug the xylem vessels in the region of a ring or other wounds, but in 
none of those instances that have come to my attention have precautions 
been taken to protect the exposed xylem. In nearly every one of my 
own experiments in which the exposed xylem of small twigs has not been 
immediately covered with a layer of melted paraffin, the leaves above the 
ring have shown withering sooner or later. Those that were protected 
rarely showed withering within the time of the experiment, and in no case 
were samples taken from stems that showed withering. In other experi¬ 
ments, however, which are not yet completed, I have obtained indications 
that rings even when protected may increase the resistence of a stem to 
the flow of water. Even if it were conclusively demonstrated, however, 
that ringing resulted in a partial plugging of the xylem, it could not be 
said with assurance that such plugging is the reason for the lower nitrogen 
and ash contents in the tissues above a ring. 
Summary 
Experiments are reported showing the effects of ringing a stem on the 
upward transfer of nitrogen and ash constituents. Data from such experi¬ 
ments with privet, peach, and lilac are presented. 
The data show that a ring distinctly hinders the movement of nitrogen 
and of ash constituents into the leaves above the ring, either when the 
ring is made in the spring before the leaves open and the new xylem is 
laid down, or when it is made in the summer after they have opened and 
the new xylem is partly or fully formed. 
When sodium nitrate, with or without other nutrient salts, is added to 
the soil, the nitrogen and ash contents of the leaves from unringed stems 
increase to a much greater extent than do those of the leaves from ringed 
stems. This is true whether data are expressed per unit of dry weight, per 
unit of leaf surface, or as absolute quantities. 
The stems also were analyzed to determine whether or not the low 
nitrogen content of the leaves could be accounted for by accumulation of 
nitrogen in the stems. These analyses, whether of the entire stem or of 
the wood and bark separately, showed a lesser content in the ringed stems. 
A single experiment was tried in which an attempt was made to eliminate 
