g4 TRANSLOCATION IN PLANTS 



tial release of their stored nitrogen. In another series, 

 where the stamp method was used to determine true 

 changes and where the growing shoots were cut off, scald- 

 ing the stem resulted in a slightly greater gain of nitrogen 

 in the leaves during the day and less loss during the night. 

 These slight differences again were probably due to the 

 prevention of transport to the roots, and to the greater 

 release from starved roots. 



Chang also determined the influence of killing the roots 

 on nitrogen absorption and distribution. The roots were 

 killed by placing the pots in scalding water for ten minutes. 

 Data from this experiment are presented in Table 15. 

 During the day the leaves of such plants absorbed signi- 

 ficantly more nitrogen than did those of check plants. 

 The shoots absorbed sHghtly more, but the difference was 

 not statistically significant. Taking the leaves and shoots 

 together the differences were not significant. At night 

 the leaves of the root-killed plants lost slightly less than 

 the normal leaves, but the difference was not significant. 

 It would seem then that killing the roots has not appreci- 

 ably altered the absorption or movement of nitrogen to 

 the tops. 



These findings of Chang's tend to support those of 

 Maskell and Mason, but I am not convinced that they 

 represent normal behavior. In the first place, in order to 

 show measurable and significant changes over 12-hour 

 periods, nitrate was added at concentrations much in 

 excess of those normally found in soils. As pointed out 

 earlier in this section, high concentrations can be expected 

 to lead to unusual leakage into the xylem, where transpira- 

 tion would carry it to the leaves. In the second place, 

 starvation of the roots would tend to result in still less 

 retention and more seepage into the xylem. As seen in 

 Table 14, the roots of the stem-scalded plants retained less 

 nitrogen, although the tops of those same plants actually 

 absorbed significantly more nitrogen than the check plants 

 and the plant as a whole, including the roots, actually had 



