of which
Darwin received specimens of the moth which there visits the flower,
unfortunately so much broken as to be useless (see "Life and Letters,"
III., page 284).)

Down, March 25th [1874].

I am glad to hear about the Hedychium, and how soon you have got an
answer! I hope that the wings of the Sphinx will hereafter prove to
be bedaubed with pollen, for the case will then prove a fine bit of
prophecy from the structure of a flower to special and new means of
fertilisation.

By the way, I suppose you have noticed what a grand appearance the plant
makes when the green capsules open, and display the orange and crimson
seeds and interior, so as to attract birds, like the pale buff flowers
to attract dusk-flying lepidoptera. I presume you do not want seeds of
this plant, as I have plenty from artificial fertilisation.

(723/2. In "Nature," June 22nd, 1876, page 173, Hermann Muller
communicated F. Muller's observation on the fertilisation of a
bright-red-flowered species of Hedychium, which is visited by
Callidryas, chiefly the males of C. Philea. The pollen is carried by the
tips of the butterfly's wing, to which it is temporarily fixed by the
slimy layer produced by the degeneration of the anther-wall.

LETTER 724. TO W. THISELTON-DYER. Down, June 4th [1874].

I am greatly obliged to you about the Opuntia, and shall be glad if you
can remember Catalpa. I wish some facts on the action of water, because
I have been so surprised at a stream not acting on Dionoea and Drosera.
(724/1. See Pfeffer, "Untersuchungen Bot. Inst. zu Tubingen," Bd.
I., 1885, page 518. Pfeffer shows that in some cases--Drosera, for
instance--water produces movement only when it contains fine particles
in suspension. According to Pfeffer the stamens of Berberis, and the
stigma of Mimulus, are both stimulated by gelatine, the action of which
is, generally speaking, equivalent to that of water.) Water does not
act on the stamens of Berberis, but it does on the stigma of Mimulus.
It causes the flowers of the bedding-out Mesembryanthemum and Drosera
to close, but it has not this effect on Gazania and the daisy, so I can
make out no rule.

I hope you are going on with Nepenthes; and if so, you will perhaps like
to hear that I have just found out that Pinguicula can digest albumen,
gelatine, etc. If a bit of glass or wood is placed on a leaf, the
secretion is not increased; but if an insect or animal-matter is thus
placed, the secretion is greatl