322 PRINCIPLES OF BOTANY, ETC: 
The style indeed of some flowers seems to possess » 
much irritability, as it follows the stamens with its 
stigma. 
The closing and opening of some flowers called 
their Vigiliae (§ 7), does not belong to this subject, 
though it may occasionally contribute something to 
the impregnation of flowers. It seems to depend 
on an increased contractility, or on an accumu- 
lation of the strong smelling transpirable matter. 
On the first it certainly depends in those flowers 
which, as it were, indicate rain, that is, shut them- 
selves soon before rain falls. ‘Lhe fibre in the pe- 
tals seems to act as a hygrometer, as in Calendula 
pluvialts, hybrida; Bellis perennis, and the . like. 
Something similar happens | in the Oenothera, though 
it remains open during rain. Perhaps some flowers, 
especially of the class Syngenesia, close in the even- 
ing for the very same reason. ‘The Hesperis ¢ristis 
and ‘some others, which open in the evening, and 
diffuse their fragrant odours, unfold themselves at 
night time, by reason of the accumulated perspir- 
able matter. But how shall we account for the 
Nymphaea alba opening in the forenoon, and clos- 
ing again about four o’clock in the afternoon, and 
then remaining till the next morning immersed in 
water ? 
§ 291. 
Koelreuter examined, in a very laborious manner, 
how many globules of pollen might be required to. 
complete an impregnation, His chief discoveries 
on this point are as follow: 
All 
