From Isaac Anderson-Henry   24 April 1863

My dear Sir

I embrace the first leisure to thank you for your very obliging note of the 20^th Inst.¹ and the beautifully executed likeness of yourself so kindly accorded to me.² I have no Carte else I am so proud to possess

I was not a little struck to learn that they had got at Kew the supposed hybrid Bryanthus (erectus) wild from North America. Having a Letter from D^r Hooker by the same post which brought me yours, I have in my answer embraced the opportunity of asking him about it.³ May it not be the B. Gmelini a true north American Species, not previously introduced and noticed by D Don in Edin: Phil: Journal 17 p 160.?⁴ At same time there is, I must confess, a mystery about Mr Cunninghams hybrid, (B. erectus)   His nephew now in a Nursery (Messrs Lawsons) hard by here, owned to me that his uncle was not quite certain of its parentage tho he believed it to be as given out,—viz a cross between the Rhod^s. Chamæcistus & a Menziesia.⁵ I think I mentioned to you that I was at that time at work myself attempting a mule between these same things—but I made the Rhodothamnus, and not the Menziesia the seed bearer,—& did not succeed.⁶ On hearing of Mr C’s cross, I inverted the X, and made Menziesia (Phyllodoce) Cærulea the female, & the R Chamæcistus the male parent which succeeded and from the seeds I raised one or two plants, which I lost early by the incursion of a snail. I then held that those in that order must have been the parents of the B. erectus. I have this year wrought the R. Chamæcistus on both, viz^t on the Phyllodoce (M) Cærulea and M. empetriformis. I am not sure that any one of the X^s on M. Cærulea has taken—but all of those (4 or 5) on the empetriformis seem to have taken, & the pods are already unmistakeably swollen with the ripening seeds. This looks like confirmation of Mr C’s selection and success. And I need not say that long experience (20 years of it) has made me most careful by previous emasculation, &^c, to secure against the interference of insects

Many many thanks for your most interesting Paper on the Linum family.⁷ I wrought upon that tribe last year, and have, if true, one cross from it—viz^t. L. rubrum Grandiflorum (annual) crossed on L. album, a perennial, the plants from which are now six inches high. But I was grievously puzzled & perplexed by the varying forms of the sexual organs on the different species,— in so much that I began to conclude from these and the want of success that Botanists had erred in the arrangement of the tribe, & that several species must be removed to another family. I wrought on a great many sp^s.— L. trigynum (with its 3 styles) L. flavum, L. perenne, L Corymbiflorum, yellow (a most obstinate thing which bore seed in no form), L. album a fine large white flowered perennial, L. flavum (which likewise bore no seed) and L. rubrum Grandiflorum— The L. trigynum let alone was the best seed bearer of them all; but I accomplished no certain cross upon it. I have the whole in array for further operations this year, & with the light you have thrown upon the genus, I will now resume my experiments with fresh avidity⁸

If I remember aright, I was perplexed in the same way in the Phlox family; with these short and long stamens—and perhaps it was from this cause & not falling on the corresponding styles, that I failed often, where I had reckoned success certain

And there are other tribes with which I have been grievously baffled, tho I cannot now recall them, for the like reason

Your discovery I am persuaded involves a law which pervades innumerable races.⁹ It is akin to Newtons discovery of the law of Gravitation¹⁰   The more I think of it, the more I am astounded by its importance & the further discoveries to which it will lead. I had long believed that different results were produceable by the different pairs of anthers on plants having these organs of unequal length,—e.g. the Geraniaceæ, the Rhodoraceæ &c &c   Now, we must have regard to the styles—the length of them—tho I incline to the belief, that this law may be found limited mainly to tribes having the anthers all of equal lengths.

Believe me; you are yet but on the threshold,—tho you have unlocked the portal in which the greatest merit lies.

If I can aid in any way do kindly suggest to me   Mean time I remain | very faithfully yours | Is. anderson Henry

I am keeping mind the experiment on the top flower of the Geranium¹¹

Many thanks for your suggestion as to Bates Travels—¹² I devour all these Books of Travels whose writers speak at all intelligibly of Natural history   But how few of them do?

P.S. On looking again, I find appearance of one pod of Menziesia Cærulea X Rhod. Chamæcistus having taken

We have formed a Microscopic Club here limited to 15 among whom are a good many Professors of the University. D^r Greville is our Chairman¹³   Will the knowledge of the microscope aid me much in any experiments you would suggest?

Charles Darwin Esqr F.R.S. &c &c