98 
JOURNAL OF THE R< 'YAL Hr»RTlCULTURAL SOCIETY. 
the erect bracts of the involucre cf the Dandehon beconie reflexed as 
soon as the fruit has ripened, thus allowing the parachute-like achenes to 
escape easily. Moving corollas are very numerous. A large series of 
plants might be mentioned of which the corollas close up either as soon 
as the sun is obscured, as species of ^Icscmhryanthemum, Anagallis 
arvciisis, Convolvulus, kc, or else at evening, such as many Composita:*, 
including the Daisy and Daindehon, re-expanding on the return of light. 
Conversely some night-flowering plants open their petals only at night, 
coiling them up by day. As an illustration Silene nutans may be taken, 
concerning which Dr. Kerner tells us * that a flower lasts three days and 
three nights. With the approach of dusk the bifid limbs of the petals 
spread out with a flat surface and fall back upon the calyx. In this 
position they remain through the night, curling themselves up into an 
incurved spiral and becoming longitudinally creased at the same time on 
the return of sunhght and a warm temperature. No sooner does evening 
return than the wrinkles disappear, the petals become smooth, uncurl 
themselves, and faUing back against the calyx the corolla is again 
expanded. 
In the Pea family there are several instances of the corolla having a 
power to move when irritated. Thus in the genera Genista and Indigo- 
fera the claws of the petals act like springs kept iu a state of tension ; 
for when the corolla is touched, as by an insect in search of honey, the 
claws suddenly curl downwards, and the petals consequently drop 
vertically ; while the stamens, previously concealed within the keel petals^ 
are violently thrown upwards, showering the bee with paUen."^ 
The movement of stamens is perhaps more curious, and apparently 
intimately connected with the phenomenon of insect pollination. As an 
example of slow movement the Grass of Parnassus, Parnassia palustrls, 
may be mentioned. In this flower each stamen in succession rises up, 
places its anther on the stigma, and having shed its pollen retires and 
falls back upon the petals. Each stamen occupies about twenty-four 
hom-3 in rising up and discharging its pollen, and takes about the same 
time to recede, the whole period being eight days, but varying according 
to circumstances of tempemture, moisture, kc. 
Berberis furnishes an instance of rapid motion, for it the stamens be 
touched at the base of the filament they instantly sprmg forward and 
strike the stigma, having previously lain cn the surface of the spreading 
petals. The effects of the irritation on the filament of Berbei-is hsixe been 
observed by Heckel. It appears that the cells of the irritable part are 
arranged in a parallel manner, the back of the filament being insensible. 
Their contents are yellow and disseminated through the cavity. After 
irritation they undergo aggregation, and contract into the centre of the 
cell, and the cell-wall is striated transversely. The ceUs of the back of 
the filament are contracted in repose but extended in irritation. 
The stamens of common Lucerne, Ifedicago sativa, as also other 
species of that genus, suddenly curve upwards and remain rigidly fixed 
in an arched condition, having been previously horizontal. i 
* Flowers and their Vnhiddcn Guests, p. 132. 
+ These I have described more fully in Journ. Linn. Soc.. ix. p. 355. and x. p. 4C8. 
^ Journ. Linn. Soc.. ix. 327. 
