Gartner 'Beitrage zur Kenntniss' etc. page 346.) As we thus
see that the open state of all ordinary flowers, and the consequent loss
of much pollen, necessitate the development of so prodigious an excess
of this precious substance, why, it may be asked, are flowers always
left open? As many plants exist throughout the vegetable kingdom which
bear cleistogene flowers, there can hardly be a doubt that all open
flowers might easily have been converted into closed ones. The graduated
steps by which this process could have been effected may be seen at the
present time in Lathyrus nissolia, Biophytum sensitivum, and several
other plants. The answer to the above question obviously is, that with
permanently closed flowers there could be no cross-fertilisation.
The frequency, almost regularity, with which pollen is transported by
insects from flower to flower, often from a considerable distance, well
deserves attention. (10/12. An experiment made by Kolreuter 'Forsetsung'
etc. 1763 page 69, affords good evidence on this head. Hibiscus
vesicarius is strongly dichogamous, its pollen being shed before the
stigmas are mature. Kolreuter marked 310 flowers, and put pollen from
other flowers on their stigmas every day, so that they were thoroughly
fertilised; and he left the same number of other flowers to the agency
of insects. Afterwards he counted the seeds of both lots: the flowers
which he had fertilised with such astonishing care produced 11,237
seeds, whilst those left to the insects produced 10,886; that is, a less
number by only 351; and this small inferiority is fully accounted for by
the insects not having worked during some days, when the weather was
cold with continued rain.
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