Other
plants when cultivated have failed to produce perfect flowers during several
successive years; and this is the case with Juncus bufonius in its native land
of Russia. Cleistogamic flowers are produced by some species late and by others
early in the season; and this agrees with the view that the first step towards
their development was due to climate; though the periods at which the two sorts
of flowers now appear must since have become much more distinctly defined. We do
not know whether too low are too high a temperature or the amount of light acts
in a direct manner on the size of the corolla, or indirectly through the male
organs being first affected. However this may be, if a plant were prevented
either early or late in the season from fully expanding its corolla, with some
reduction in its size, but with no loss of the power of self-fertilisation, then
natural selection might well complete the work and render it strictly
cleistogamic. The various organs would also, it is probable, be modified by the
peculiar conditions to which they are subjected within a completely closed
flower; also by the principle of correlated growth, and by the tendency in all
reduced organs finally to disappear. The result would be the production of
cleistogamic flowers such as we now see them; and these are admirably fitted to
yield a copious supply of seed at a wonderfully small cost to the plant.
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