r off at once, but on reflection will keep it till I
receive the plants.

LETTER 703. TO H. MULLER. Down, March 14th, 1870.

I think you have set yourself a new, very interesting, and difficult
line of research. As far as I know, no one has carefully observed the
structure of insects in relation to flowers, although so many have
now attended to the converse relation. (703/1. See Letter 462, also H.
Muller, "Fertilisation of Flowers," English Translation, page 30, on
"The insects which visit flowers." In Muller's book references are
given to several of his papers on this subject.) As I imagine few or
no insects are adapted to suck the nectar or gather the pollen of
any single family of plants, such striking adaptations can hardly, I
presume, be expected in insects as in flowers.

LETTER 704. TO T.H. FARRER (Lord Farrer).

Down, May 28th, 1870.

I suppose I must have known that the stamens recovered their former
position in Berberis (704/1. See Farrer, "Nature," II., 1870, page 164.
Lord Farrer was before H. Muller in making out the mechanism of the
barberry.), for I formerly tried experiments with anaesthetics, but I
had forgotten the facts, and I quite agree with you that it is a
sound argument that the movement is not for self-fertilisation. The
N. American barberries (Mahonia) offer a good proof to what an extent
natural crossing goes on in this genus; for it is now almost impossible
in this country to procure a true specimen of the two or three forms
originally introduced.

I hope the seeds of Passiflora will germinate, for the turning up of the
pendent flower must be full of meaning. (704/2. Darwin had (May 12th,
1870) sent to Farrer an extract from a letter from F. Muller, containing
a description of a Passiflora visited by humming-birds, in which the
long flower-stalk curls up so that "the flower itself is upright."
Another species visited by bees is described as having "dependent
flowers." In a letter, June 29th, 1870, Mr. Farrer had suggested that P.
princeps, which he described as having sub-erect flowers, is fitted for
humming-birds' visits. In another letter, October 13th, 1869, he
says that Tacsonia, which has pendent flowers and no corona, is not
fertilised by insects in English glass-houses, and may be adapted for
humming-birds. See "Life and Letters," III., page 279, for Farrer's
remarks on Tacsonia and Passiflora; also H. Muller's "Fertilisation of
Flowers," page 268, for what little is known