Its flowers are simpler and much more variable than in ordinary
garden-varieties. The process of doubling consists mainly in a change of
stamens into petals. This change is dependent on the season. On each
stem the earliest flowers are single. These are succeeded by blossoms
with one or two converted stamens, and towards the summer this number
increases gradually, attaining 10-11 and in some instances even more
altered filaments. Each year the same succession may be seen repeating
itself on the stems of [366] the old roots. Double tuberous begonias are
ordinarily absolutely sterile throughout the summer, but towards autumn
the new flowers become less and less altered, producing some normal
stamens and pistils among the majority of metamorphosed organs. From
these flowers the seeds are saved. Sometimes similar flowers occur at
the beginning of the flowering-period. Double garden-camomiles
(_Chrysanthemum inodorum plenissimum_) and many other double varieties
of garden-plants among the great family of the composites are very
sensitive to external agencies, and their flower-heads are fuller the
more favorable the external conditions. Towards the autumn many of them
produce fewer and fewer converted heads and often only these are fertile
and yield seeds.
Ascidia afford another instance of this periodicity, though ordinarily
they are by far too rare to show any regularity in their distribution.
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