It cannot be maintained that their openness is necessary for
fertility, as cleistogene flowers which are permanently closed yield a
full complement of seeds. Pollen contains much nitrogen and
phosphorus--the two most precious of all the elements for the growth of
plants--but in the case of most open flowers, a large quantity of pollen
is consumed by pollen-devouring insects, and a large quantity is
destroyed during long-continued rain. With many plants this latter evil
is guarded against, as far as is possible, by the anthers opening only
during dry weather (10/7. Mr. Blackley observed that the ripe anthers of
rye did not dehisce whilst kept under a bell-glass in a damp atmosphere,
whilst other anthers exposed to the same temperature in the open air
dehisced freely. He also found much more pollen adhering to the sticky
slides, which were attached to kites and sent high up in the atmosphere,
during the first fine and dry days after wet weather, than at other
times: 'Experimental Researches on Hay Fever' 1873 page 127.)--by the
position and form of some or all of the petals,--by the presence of
hairs, etc., and as Kerner has shown in his interesting essay, by the
movements of the petals or of the whole flower during cold and wet
weather. (10/8. 'Die Schutzmittel des Pollens' 1873.) In order to
compensate the loss of pollen in so many ways, the anthers produce a far
larger amount than is necessary for the fertilisation of the same
flower.
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