50 TRANSLOCATION IN PLANTS 



the summer when no nitrogen was added to the soil, or 

 when there were no rains to wash what was appUed into the 

 soil, no distinct increases were evident in either ringed or 

 check leaves. When expressed as a percentage of dry 

 weight, the leaves of the ringed stem showed decreases as 

 one would expect. 



Though ringing experiments of the type mentioned have 

 in every case resulted in an interference in upward transfer 

 of solutes, this in itself cannot be considered as conclusive 

 evidence that the xylem is not directly concerned in 

 translocation, for the rate of transpiration from ringed 

 branches seems commonly reduced. 



If solutes are carried in the transpiration stream, this 

 reduced transpiration may partly account for the reduction 

 in solutes carried to the ringed branch. To eliminate a 

 possible effect of transpiration, an experiment was carried 

 out with twigs of Ligustrum treated as previously described 

 in Sec. 7 and shown in Fig. 1. On all twigs there was a 

 group of four pairs of leaves at the top of the stem to 

 insure a transpiration stream through the stem. In two 

 sets of 12 stems each, rings were made immediately below 

 the upper leaves, and in one of these sets additional rings 

 were also made at the base of the defoliated parts. In all 

 three sets each twig had 4 pairs of leaves at the top, and 

 in each case a ring was present between these leaves and 

 the leaves below. This would tend to make the amounts 

 and rates of water movement through the defoliated parts 

 about equal in all instances. Since the carbohydrate 

 content of the defoliated region would be expected to 

 influence its ability to absorb or retain nitrogen, rings were 

 made at both the top and base of the defoliated region in 

 one set of twigs to insure a low carbohydrate content, and 

 at the base only in the other set to insure a high carbo- 

 hydrate content. As is clearly shown in Table 10, the 

 ring at the base of the defoliated part has interfered with 

 the movement of nitrogen into this region, both when the 

 carbohydrate content is high and when it is low, and the 

 effect is not due to an effect on transpiration. 



