The effect of nitrogen on the movement of tracers down the stolon of Saxifraga sarmentosa, with some observations on the influence of light.

The movement of applied (137)Cs and of naturally-assimilated (14)C down the long stolon of Saxifraga is strongly inhibited by confining a length of 10 to 30 cm of the stolon in an atmosphere of nitrogen. The inhibition is reversible, normal transport being restored after less then 4 h when the stolon is returned to air from 5 h in nitrogen. Callose formation does not seem to be involved. There is evidence that local darkness has a similar adverse effect on phloem transport.These findings are considered antagonistic to the pressure-flow hypothesis, but favourable to the active mass-flow theories.