differently constructed flowers; but there are some plants that produce
differently formed seeds, of which Dr. Kuhn has given a list. (Introduction/15.
'Botanische Zeitung' 1867 page 67.) With the Umbelliferae and Compositae, the
flowers that produce these seeds likewise differ, and the differences in the
structure of the seeds are of a very important nature. The causes which have led
to differences in the seeds on the same plant are not known; and it is very
doubtful whether they subserve any special end.

We now come to our second Class, that of monoecious species, or those which have
their sexes separated but borne on the same plant. The flowers necessarily
differ, but when those of one sex include rudiments of the other sex, the
difference between the two kinds is usually not great. When the difference is
great, as we see in catkin-bearing plants, this depends largely on many of the
species in this, as well as in the next or dioecious class, being fertilised by
the aid of the wind; for the male flowers have in this case to produce a
surprising amount of incoherent pollen. (Introduction/16. Delpino 'Studi sopra
uno Lignaggio Anemofilo' Firenze 1871.) Some few monoecious plants consist of
two bodies of individuals, with their flowers differing in function, though not
in structure; for certain individuals mature their pollen before the female
flowers on the same plant are ready for fertilisation, and are called
proterandrous; whilst conversely other individuals, called proterogynous, have
their stigmas mature before their pollen is ready. The purpose of this curious
functional difference obviously is to favour the cross-fertilisation of distinct
plants. A case of this kind was first observed by Delpino in the Walnut (Juglans
regia), and has since been observed with the common Nut (Corylus avellana). I
may add that according to H. Muller the individuals of some few hermaphrodite
plants differ in a like manner; some being proterandrous and others
proterogynous. (Introduction/17. Delpino 'Ult. Osservazioni sulla Dicogamia'
part 2 fasc 2 page 337. Mr. Wetterhan and H. Muller on Corylus 'Nature' volume
11 page 507 and 1875 page 26. On proterandrous and proterogynous hermaphrodite