My dear M^r. Darwin

I need hardly say that I shall feel much pleased if you can make any use of the small fact noticed by me concerning Monkshood. I fear however that I can give you but very scanty details.¹

In 1871 I was in a part of Switzerland where there was great abundance of blue Aconitum Napellus, with a sprinkling also of white specimens of the same species. I chanced one day to notice that all the blossoms from white specimen which I was examining had a hole made through the corolla for the theft of nectar, while the blossoms of a blue specimen which I was comparing with the white one had not been similarly mistreated.

Thinking that this difference of treatment might account for the difference in the abundance of the two varieties, I collected and examined a hundred racemes of each variety.

Not a single fully opened blossom on the 100 white specimens was without the nibbled hole; while not a single blossom on the 100 blue specimens had it.² One or two however of the blue blossoms had been gnawed irregularly by some animal or other, probably a slug or snail.

I do not know whether the Aconitum is sterile, when insects are excluded.³

I wish I could give you more information, but this is all I have.

I am reminded by this question of colour of a passage which I noted some year or two ago in Mead on the Plague, written some 140 years ago, and thought would interest you as bearing on the correlation of colour and disease. “I am well aware that there are plagues among animals, which do not indifferently affect all kinds of them, some being confined to a particular species (like the disease of the Black Cattle here, a few years since, which neither proved infectious to other brutes nor to men;) yet it has always been observed that the true plague among men has been destructive to all Creatures of what kind soever”⁴

Believe me | Y^rs. very sincerely | W. Ogle.