top, and female flowers at the
base.

[Illustration: FIG. 100.--Spike of _Carex acuta_, with female flowers at
the summit.]

On the subject of this section the reader may consult A.
Braun,. 'Das Individ.,' 1853, p. 65. Caspary, 'De Abietin.
flor. fem. struct. morphol.' Schleiden. 'Principles,' English
edition, p. 299. Mohl, 'Verm. Schrift.,' p. 45. Meyen in
'Wiegm. Archiv.,' 1838, p. 155. Cramer, 'Bildungsabweich,' p.
4, tab. v, figs. 13-17. Parlatore, 'Ann. Sc. Nat.,' ser. iv,
vol. xvi, p. 215, tab. 13A. See also under the head of
Prolification, Substitutions, &c.

=Change from the monoecious to the dioecious condition.=--This is of
less frequent occurrence than might have been anticipated. In the
'Gardeners' Chronicle,' 1847, pp. 541 and 558, several instances are
noted of walnut trees bearing female flowers to the exclusion of males.
The mulberry tree has also been noticed to produce female blossoms only,
while in other plants male flowers only are developed.

It seems probable that the age of the plant may have something to do
with this production of flowers of one sex to the exclusion of the
other.

=Change from the dioecious to the monoecious condition.--Androgynism.=--
This is of far more common occurrence than the preceding.

[Illustration: FIG. 101.--Monoecious inflorescence of Hop.]

In the hop (_Humulus Lupulus_), when monoecious, the female catkins
are usually borne on the ends of the branches as shown in the cut (fig.
101), and a similar thing has been noticed in _Urtica dioica_ by Clos,
'Bull. Soc. Bot. France,' vol. 9, p. 7.

Baillon ('Etudes du groupe des Euphorbiacees,' p. 205) mentions the
following species of that order as having been seen by him with
monoecious inflorescence: _Schismatopera distichophylla_, _Mozinna
peltata_, _Hermesia castaneifolia_. Oliver mentions ('Hook. Icon.
Plant.,' t. 1044) that in _Leitneria floridana_ the upper scales of the
male catkin occasionally subtend an ovary.

It would seem that external conditions have some effect in determining
the formation of one sex, as in some species of _Carex_, while in the
case of _Salix repens_, Hampe[192] says that when grown partially or for
a time under water, those twigs which are thrust up above the surface
bear female flowers, while those twigs that blossom after the water is
dried up, produce male flowers only.

Carriere[193] says that a plant of _Stauntonia latifolia_ which for s