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Darwin, Charles, 1809-1882

"The Different Forms of Flowers on Plants of the Same Species"


Although the majority of the species in the large genus Oxalis seem to be
trimorphic, some are homostyled, that is, exist under a single form; for
instance the common O. acetosella, and according to Hildebrand two other widely
distributed European species, O. stricta and corniculata. Fritz Muller also
informs me that a similarly constituted species is found in St. Catharina, and
that it is quite fertile with its own pollen when insects are excluded. The
stigmas of O. stricta and of another homostyled species, namely O.
tropaeoloides, commonly stand on a level with the upper anthers, and both these
species are likewise quite fertile when insects are excluded.
With respect to O. acetosella, Hildebrand says that in all the many specimens
examined by him the pistil exceeded the longer stamens in length. I procured 108
flowers from the same number of plants growing in three distant parts of
England; of these 86 had their stigmas projecting considerably above, whilst 22
had them nearly on a level with the upper anthers. In one lot of 17 flowers from
the same wood, the stigmas in every flower projected fully as much above the
upper anthers as these stood above the lower anthers. So that these plants might
fairly be compared with the long-styled form of a heterostyled species; and I at
first thought that O. acetosella was trimorphic.


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