details, that some plants of Caltha palustris produce only male flowers, and
that these live mingled with the hermaphrodites. (Introduction/20. 'Geographie
Botanique' tome 4 page 488.) The rarity of such cases as this last one is
remarkable, as the presence of hermaphrodite and male flowers on the same
individual is not an unusual occurrence; it would appear as if nature did not
think it worth while to devote a distinct individual to the production of
pollen, excepting when this was indispensably necessary, as in the case of
dioecious species.

I have now finished my brief sketch of the several cases, as far as known to me,
in which flowers differing in structure or in function are produced by the same
species of plant. Full details will be given in the following chapters with
respect to many of these plants. I will begin with the heterostyled, then pass
on to certain dioecious, sub-dioecious, and polygamous species, and end with the
cleistogamic. For the convenience of the reader, and to save space, the less
important cases and details have been printed in smaller type [].

I cannot close this Introduction without expressing my warm thanks to Dr. Hooker
for supplying me with specimens and for other aid; and to Mr. Thiselton Dyer and
Professor Oliver for giving me much information and other assistance. Professor
Asa Gray, also, has uniformly aided me in many ways. To Fritz Muller of St.
Catharina, in Brazil, I am indebted for many dried flowers of heterostyled
plants, often accompanied with valuable notes.


CHAPTER I.

HETEROSTYLED DIMORPHIC PLANTS: PRIMULACEAE.

Primula veris or the cowslip.