Botany; Geotropism; Plants -- Irritability and movements
We have as yet referred only to the different positions of the leaflets
of L. pubescens at night; but the petioles likewise differ in their
movements. That of a young leaf which formed a highly inclined star at
night, stood at noon at 42° above the horizon, and during the night at
72°, so had risen 30°. The petiole of another leaf, the leaflets of
which occupied a similar position at night, rose only 6°. On the other
hand, the petiole of a leaf with all its leaflets sloping down at
night, fell at this time 4°. The petioles of two rather older leaves
were subsequently observed; both of which stood during the day at
exactly the same angle, viz., 50° above the horizon, and one of these
rose 7°–8°, and the other fell 3°–4° at night. We meet with cases like
that of L. pubescens with some other species. On a single plant of L.
mutabilis some leaves, which stood horizontally during the day, formed
highly inclined stars at night, and the petiole of one rose 7°. Other
leaves which likewise stood horizontally during the day, had at night
all their leaflets sloping downwards at 46° beneath the horizon, but
their petioles had hardly moved. Again, L. luteus offered a still more
remarkable case, for on two leaves, the leaflets which stood at noon at
about 45° above the horizon, rose at night to 65° and 69°, so that they
formed a hollow cone with steep sides. Four leaves on the same plant,
which had their leaflets horizontal at noon, formed vertical stars at
night; and three other leaves equally horizontal at noon, had all their
leaflets sloping downwards at night. So that the leaves on this one
plant assumed at night three different positions. Though we cannot
account for this fact, we can see that such a stock might readily give
birth to species having widely different nyctitropic habits.
Little more need be said about the sleep of the species of Lupinus;
several, namely, L. polyphyllus, nanus, Menziesii, speciosus,
and albifrons, though observed out of doors and in the greenhouse, did
not change the position of their leaves sufficiently at night to be
said to sleep. From observations made on two sleeping species, it
appears that, as with Tropaeolum majus, the leaves must be well
illuminated during the day in order to sleep at night. For several
plants, kept all day in a sitting-room with north-east windows, did not
sleep at night; but when the pots were placed on the following day out
of doors, and were brought in at night, they slept in the usual manner.
the trial was repeated on the following day and night with the same
result.
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