The Sentinel. [volume] (Trenton, N.J.) 1880-1882, 1881-08-20
Flower Clocks and BarOmeters.

Even the most casual observer of ma
ture must have noticed the closing of
certain flowers upon the partial or en-
tire withdrawal of light. Thus the
click weed is sensitive to cloudy
weather and acts almost as barometer,
and every one knows the action of the
pimpernel," or "poor mans weather
grass" (Anagallis arvensis, L.. This
pretty little plant is frequent on New
port island, where / have found it, es-
pecially on the cliffs beyond the first
beach. It is adventurous from Europe.
Tennyson, who is an acute observer, says
of it: "The pimpernel dozed on the
lea" The well-known Marvel of Peru
is also called "Four O'clock" from its
habit Of opening at about that hour.
If we watch any plant we shall find that
it has pretty definite time Of expand
ing or closing it's petals, as well as
particular way of doing it. Botanists,
then, speak OF the waking and sleeping
conditions Of the plant, and much re-
search has been bestowed upon the sub
| iect in order to find out the physical
action and cause of the phenomena. In
his recent volume on Movement in
Plants" Mr.. Darwin gives the results
Of his painstaking Investigations of this
and kindred subjects. AS generally
happens in his work, while be is steadily
aiming at some particular point, he dis
poses of any quantity of obscurities as
side issues on the way.
Linn@us, noting the precise times of
opening and closing of flowers, con-
structed floral clock in his gardens at
Upsat, where the hours were indicated
by the conditions of different plants.
Afterward DeCandolle did the same for
the latitude Of Paris. The clock of
Iinn@us in Sweden runs slower than
that of DeCandolle in France. Climate
as well as latitude, and particular sea-
sons also, would influence this sensitive
horologe Those interested will find
DeCandolle's list given in Figuier's
vegetable World" American edition,
page 1874.
OF a few familiar plants the hours Of
opening are about as follows: Morning
glory, 3 to A. NJ; pimpernel, 8 to 10
A. NJ; Marvel OF Peru, to P. NJ;
evening primrose, 5 to P. NJ; night
blooming cereus, 7 to 8P. N.
''Thus in each flower and simple bell,
That III our path betrodden lie,
Are sweet remembrancers who tell
How fast the winged moments fly"
The hours of closing are as definite as
those of opening, and thus we may az
range quite dial, the hours being indi-
Gated by particular plants. The plants
may be confused by means Of artificial
light, but upon withdrawal of the I'M
natural conditions, will, sooner or later,
resume their normal record.
1t is curious to watch the different
attitudes flowers assume in repose In
the botanic garden in Cambridge the
writer used to go out toward evening to
watch the changes. sThe movements
ere sometimes very quick, especially
chose of the foliage, which also has its
time of sleep. Thus in the little Mar
silia, plant, with four OBJ cordate
leaflets, these turn in upon each other
from the expanded condition, SO as to
meet face to face. There is quite per-
ceptible little "click" when the move
ment occurs. The petals of some plants
droop in slumber; others fold crossways:
still others curl up lengthwise. So with
the rayforets of the Composite. The
whole aspect of garden is, hence, quite
changed in the evening. In fact, it does
not DO to allow our Investigations to
ease with the daylight.