My dear Sir

Your Letter of the 2^d. reached me at my place in Perthshire from which I returned last night.¹ I cannot withdraw from the estimate I expressed of the importance and value of your discovery.—² You have let in the first ray of what I believe must burst in sunlight sooner or later

I have already, by the severest tests, proved you right among the Primulas.³ I took three several plants of the Common garden P. Polyanthus—got them potted & put under Glass. I thereafter carefully labelled them, A, B, & C,—noting on the labels & in a Book, their respective properties. A indicated by purple thread had a short style and long anthers.— B, indicated by yellow silk had a long style and Short anthers.— C indicated by red worsted, like A, had a short style and long anthers.

Having secured against all interference by insects or otherwise I effected the experiment of fertilisation on 17 April last

On the plant A I did 2 flowers with the pollen of B., and one flower with its own pollen—carefully marking each with the appropriate thread.

On the plant B I did 4, two with the Pollen of A & two with its own pollen, marking as above

On the plant C I did one with the pollen of B. and one with its own pollen

Result

On A. the two done with the pollen of B. have already fine swollen seed vessels— the one done with its own pollen is a total failure

On B. all are failures—and the reason is this: The plant was sickly when I made the operation—and some days thereafter I found it nearly dead— I barely kept it alive by removal from a warm to a cold greenhouse

On C I did two flowers as I have said.— The one with the pollen of B has its seed pod swollen beautifully—the other, with its own, is a total failure

I have attempted a cross on P Sinensis with long style with the long anthered primrose known here as “Hose in hose” a mere form of P. polyanthus   And tho’ I cannot be confident it seems to have taken. The seed vessel at all events is swelling finely; but this, as you may have observed, is no sure test— And I confess I have my doubts—just because the cross is one of the severest—the Sinensis belonging, I hold, to a separate tho allied genus. Of this again

Meantime I regard the above results as clearly confirmatory of those of your published Experiments—and that the law you have discovered is established in nature

Thanks for your suggestions about the Pelargoniums—upon which I shall try my hand forthwith— So also of the Linums and Phloxes.⁴ I had sown a potful of their seeds last year and wait their coming up. I have had my patience severely taxed in this way. I have got seeds to vegetate often, especially seeds from abroad after lying dormant for more than two years

In a Letter I had from D^r Hooker by the same post with yours— He says “The Bryanthus which M^r Darwin alludes to is a dried specimen from the M^ts. of California. If B. erectus is a hybrid (and no doubt you are correct) it is more probably a cross between 2 Bryanthii than with a Rhododendron.”⁵ All probable if M^r Cunningham had had the only two Bryanthii then (or perhaps yet) known, to make the X with—⁶ But I presume they are yet to introduce. My Experiments this year may put this question to the test

D^r Hooker suggests to me “to try and cross American individuals of European plants with European Individuals. E.g. (he asks) would an American plant of Caltha palustris be as fertile with an English as with an American?” I must, in my manifold crosses have united Americans, as I have done innumerable Asiatics, with Europeans—eg among the Rhododendrons.—⁷ As to the fertility of the hybrid, that may be another thing

I have got American Brambles, as well as Asiatic among which I have long resolved to try experiments to improve, if possible, the fruits of our European species—⁸ And I am especially to try a union between the Blackberry & Raspberry—⁹ And having my eye to your discovery, I am to apply all kinds of anthers, short and long, inner & outer, & in different states of maturity

Believe me ever | Yours very Sincerely | Is. anderson Henry

Thanks for your information about the Microscope.¹⁰ But I had got one at a high price ere your Letter came, which however I required otherwise

I was told today that poor Donald Beaton was dying—at least, in a hopeless way¹¹

Charles Darwin Esq F.R.S. | &c &c