My dear Sir

I thank you for your very interesting letter, and I honour you for your laborious and careful experiments.¹ No one knows till he tries how many unexpected obstacles arise in subjecting plants to experiments.

I can think of no suggestions to make; but I may just mention that I had intended to try the effects of touching the dampened seeds with the minutest drop of formic acid at the end of a sharp glass rod, so as to imitate the possible action of the sting of the ant.² I heartily hope that you may be rewarded by coming to some definite result; but I fail 5 times out of 6 in my own experiments. I have lately been trying some with poor success and suppose that I have done too much, for I have been completely knocked up for some days.³

That is an extremely curious fact which you mention about the old Jewish law.⁴

With all good wishes, | Your’s very sincerely | Ch. Darwin