45 m. from the time when the lower
sides of the tips were touched with the caustic.
Phaseolus multiflorus.--Eight radicles, serving as controls, were extended
horizontally, some in damp friable peat and some in damp air. They all
became (temp 20o - 21o C.) plainly geotropic in 8 h. 30 m., for they then
stood at an average angle of 63o beneath the horizon. A rather greater
length of the radicle is bowed downwards by geotropism than in the case of
Vicia faba,
[page 536]
that is to say, rather more than 6 mm. as measured from the apex of the
root-cap. Nine other radicles were similarly extended, three in damp peat
and six in damp air, and dry caustic was held transversely to their tips
during 4 or 5 seconds. Three of their tips were afterwards examined: in (1)
a length of 0.68 mm. was discoloured, of which the basal 0.136 mm. was
yellow, the apical part being black; in (2) the discoloration was 0.65 mm.
in length, of which the basal 0.04 mm. was yellow; in (3) the discoloration
was 0.6 mm. in length, of which the basal 0.13 mm. was yellow. Therefore
less than 1 mm.
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