Dear Sir,

I am much obliged for your letter of the 5^th. It had never occurred to me to try the effect of dry heat upon pollen.¹ I have frequently boiled it to see if this would prevent the molecular motion of the granular matter. The whole question of the action of various agents upon pollen had been reserved for a future course of experiments but my mind had dwelt more particularly upon what might be the effect of solutions of various bodies upon the vitality of pollen. The problem of cure has still to be solved and really resolves itself principally into a question of prophylaxis. I fear it will prove to be the most formidable and difficult part of the task I originally set myself. I shall however make an effort to find a cure. Even if I fail I shall be sure to get some good from the effort.

The fact of pollen being in some plants coherent and in some incoherent, was not quite unknown to me, but I was not aware that the thing had been thoroughly investigated;² and before getting your letter it had not struck me as being a matter of any great importance in discussing the causes of hay-fever. I see now, however, that it has a very important bearing upon the subject, and I very much regret that it should have escaped my attention.

When I tell you that all my investigations have had to be made with the hourly recurring demands of a moderately large practice³ pressing upon me, you will quite understand that the pull must have been great at times, and that it has not been an easy task to take note of every thing belonging to the subject. I am much obliged to you for drawing my attention to the matter.

I must also thank you for the information you give me about the distribution of pollen, the facts are to me very interesting. As soon as I begin my experiments again I shall not fail to try the effect of dry heat upon pollen but as I am only just beginning to feel that my usual summer attack is on the turn I have not courage enough to begin experimenting until I have had a little rest.

In conclusion allow me to say that any suggestion you may wish to make or any fact you would like to communicate will be very thankfully received by me at any time.

Apologising for troubling you with this letter & with best wishes.

I Remain Dear Sir | Yours Very Sincerely | Cha^s H Blackley

Cha^s Darwin Esq MA. F.R.S. &c

P.S. I omitted to say that empty pollen cells are generally found on the slides, but, as far as I can now remember, these do not amount to more than two or three per cent.⁴ | CHB