Oxalis (Biophytum) sensitiva.--The cotyledons are highly remarkable from
the amplitude and rapidity of their movements during the day. The angles at
which they stood above or beneath the horizon were measured at short
intervals of time; and we regret that their course was not traced during
the whole day. We will give only a few of the measurements, which were made
whilst the seedlings were exposed to a temperature of 22 1/2o to 24 ?
decrees C. One cotyledon rose 70o in 11 m.; another, on a distinct
seedling, fell 80o in 12 m. Immediately before this latter fall the same
cotyledon had risen from a vertically downward to a vertically upward
position in 1 h. 48 m., and had therefore passed through 180o in under 2 h.
We have met with no other instance of a circumnutating movement of such
great amplitude as 180o; nor of such rapidity of movement as the passage
through 80o in 12 m. The cotyledons of this plant sleep at night by rising
[page 27]
vertically and coming into close contact. This upward movement differs from
one of the great diurnal oscillations above described only by the position
being permanent during the night and by its periodicity, as it always
commences late in the evening.
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