52 TRANSLOCATION IN PLANTS 



the stems with no ring below the defoliated part may give 

 no indication of the total amount that has moved into this 

 region. This part is in complete connection with the rest 

 of the plant and one would not expect it to accumulate 

 materials in excess of amounts found in other parts. Per- 

 haps the amount finally found is only one-half or even 

 one-tenth of the amount that may have moved in and out 

 again. Above the ring, however, in group 3, there was no 

 opportunity (except by leaching which should be similar 

 in all treatments) for the nitrogen to leave the tissues after 

 it had once entered. Even after the long period of 39 

 days, only about 71 per cent as much total nitrogen had 

 entered this tissue as had been retained by the other stems, 

 which may have received and reexported many times the 

 amount finally found. 



Furthermore, though the twigs with the single ring at 

 the base had more nitrogen than those with two rings, this 

 does not mean that all these twigs at the beginning had a 

 low nitrogen content similar to the double-ringed stems 

 at the end of the experiment. Respiration must have 

 appreciably reduced the carbohydrate content between the 

 two rings. This would tend to result in a decomposition 

 of the proteins and the production of more soluble forms of 

 nitrogen. This would very likely result in some release 

 and leaching of nitrogen into the transpiration stream and 

 thus tend to reduce the amount present. Some nitrogen 

 might similarly enter with the transpiration stream from 

 below, but the low carbohydrate between the two rings 

 would reduce the tendency to retain any passing through. 

 Maskell and Mason (1929a) found an appreciable loss of 

 nitrogen from between rings on the stem of cotton, which 

 can probably be accounted for on the same basis, that is, 

 release of nitrogen from starved tissues. In a later paper, 

 however (1930a), they observed a slight increase in defoli- 

 ated parts between rings. Since the amount originally 

 present in the stem was not determined and since there 

 are no data showing the amounts passing into, and out of, 

 the bark when phloem connections are not broken, no 



