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Philip Gosse, moreover, was engaged at this time in the delightful task of helping Charles Darwin to develop his various important theories, and the three succeeding letters (now first published) may be taken as specimens of this correspondence:—

"Down, Bromley, Kent, September 22, 1856.

MY DEAR SIR,

I want much to beg a little information from you.

I am working hard at the general question of variation, and paying for this end special attention to domestic pigeons. This leads me to search out how many species are truly rock pigeons, i.e. do not roost or willingly perch or nest in trees. Tenminck puts C. leucocephala (your bald-pate) under this category. Can this be the case ? Is the loud coo to which you refer in your interesting Sojourn like that of the domestic pigeon? I see in this same work you speak of rabbits run wild; I am paying much attention to them and am making a large collection of their skeletons. Do you think you could get any of your zealous and excellent correspondents to send me an adult (neck not broken) female specimen? It would be of great"

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value to me. It might be sent, I should think, in a jar with profusion of salt and split in the abdomen. I should also be very glad to have one of the wild canary birds for the same object; I have a specimen in spirits from Madeira.
 Do you think you could aid me in this, and shall you be inclined to forgive so very troublesome a request? As I have found the good nature of fellow-naturalists almost unbounded, I will venture further to state that the body of any domestic or fancy pigeon which has been for some generations in the West Indies would be of extreme interest, as I am collecting specimens from all quarters of the world.

Trusting to your forgiveness,

I remain, my dear sir,

Yours sincerely,

CH. DARWIN.

"Down, Bromley, Kent, September 28, 1856.

MY DEAR SIR,

I thank you warmly for your extremely kind letter, and for your information about the bald-pate, which is quite sufficient. When we meet next I shall beg to hear the actual coo!

I will by this very post write to Mr. Hill, and will venture to use your name as an introduction, which I am sure will avail me much ; so you need take no trouble on the subject, as using your name will be all that I should require. With my sincere thanks,

Yours truly,

CH. DARWIN.

I am very anxious to get all cases of the transport of plants or animals to distant islands. I have been trying the effects of salt water on the vitality of seeds

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 — their powers of floatation — whether earth sticks to birds' feet or base of beak, and I am experimenting whether small seeds are ever enclosed in such earth, etc. Can you remember any facts? But of all cases whatever, the means of transport (and such I must think exist) of land mollusca utterly puzzle me most I should be very grateful for any light."

"Moor Park, Farnham, Surrey, April 27, 1857.

MY DEAR SIR,

I have thought that perhaps in course of the summer you would have an opportunity, and would be so very kind as to try a little experiment for me. I think I can tell best what I want by telling what I have done. The wide distribution of some species of fresh-water molluscs has long been a great perplexity to me ; I have just lately hatched a lot, and it occurred to me that when first born they might perhaps have not acquired phytophagous habits, and might perhaps like nibbling at a duck's foot. Whether this is so I do not know, and indeed do not believe it is so, but I found when there were many very young molluscs in a small vessel with aquatic plants, amongst which I placed a dried duck's foot, that the little barely visible shells often crawled over it, and then they adhered so firmly that they could not be shaken off, and that the foot being kept out of water in a damp atmosphere, the little molluscs survived well ten, twelve, or fifteen hours, and a few even twenty-four hours. And thus, I believe, it must be the fresh-water shells get from pond to pond, and even to islands out at sea. A heron fishing, for instance, and then startled, might well on a rainy day carry a young mollusc for a long distance. Now you will remember that E. Forbes argues chiefly from the

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difficulty of imagining how littoral sea-molluscs could cross tracts of open ocean, that islands, such as Madeira, must have been joined by continuous land to Europe; which seems to me, for many reasons, very rash reasoning. Now, what I want to beg of you is, that you would try an analogous experiment with some sea-mollusc, especially any strictly littoral species — hatching them in numbers in a smallish vessel and seeing whether, either in larval or young shell state f they can adhere to a bird's foot and survive, say, ten hours in damp atmosphere out of water. It may seem a trifling experiment, but seeing what enormous conclusions poor Forbes drew from his belief that he knew all means of distribution of sea-animalcules, it seems to me worth trying. My health has lately been very indifferent, and I have come here for a fortnight's water-cure.

I owe to using your name a most kind and most valuable correspondent, in Mr. Hill of Spanish Town. I hope you will forgive my troubling you on the above points, and believe me, my dear sir,

Yours very sincerely,

CH. DARWIN.

P.S. — Can you tell me, you who have so watched all sea-nature, whether male crustaceans ever fight for the females? is the female sex in the sea, like on the land, 'teterrima belli causa?' I beg you not to answer this letter, without you can and will be so kind as to tell me about crustacean battles, if such there be."

To this my father replied with ample notes, as, & little later, he helped Darwin to collect facts with regard to the agency of bees in the fertilization of papilionaceous flowers.

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C. DARWIN to P. H. GOSSE.

Down, June 2, 1863.

MY DEAR SIR,

 It would give me real pleasure to resolve your doubts, but I cannot. I can give only suspicions and my grounds for them. I should think the non-viscidity of the stigmatic hollow was due to the plant not living under its natural conditions. Please see what I have said on Acropera. An excellent observer, Mr. J. Scott, of the Botanical Gardens, Edinburgh, finds all that I say accurate, but nothing daunted, he with the knife enlarged the orifice, and forced in pollen-masses; or he simply stuck them into the contracted orifice  without coming into contact with the stigmatic surface, which is hardly at all viscid; when, lo and behold, pollen tubes were emitted and fine seed capsules obtained. This was effected with Acropera Loddigesii; but I have no doubt that I have blundered badly about A. luteola. I mention all this because, as Mr. Scott remarks, as the plant is in our hot-houses, it is quite incredible it ever could be fertilized in its native land.  The whole case is an utter enigma to me. Probably you are aware that there are cases (and it is one of the oddest facts in physiology) of plants which under culture have their sexual functions in so strange a condition, that though their pollen and ovules are in a sound state and can fertilize and be fertilized  by distinct but allied species, they cannot fertilize themselves. Now, Mr. Scott has found this the case  with certain orchids, which again shows sexual disturbance.

He had read a paper at the Botanical Society of Edinburgh, and I dare say an abstract which I have seen will appear in the Gardener's Chronicle; but blunders have crept in in copying, and parts are barely

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intelligible. How insects act with your Stanhopea I will not pretend to conjecture. In many cases I believe the acutest man could not conjecture without seeing the insect at work. I could name common English plants in this predicament. But the musk orchis is a case in point. Since publishing, my son and myself have watched the plant and seen the pollinia removed, and where do you think they invariably adhere in dozens of specimens?-always to the joint of the femur with the trochanter of the first pair of legs, and nowhere else. When one sees such adaptation as this, it would be helpless to conjecture on the Stanhopea till we  know what insect visits it. I have fully proved that my strong suspicion was correct that with many of our English orchids no nectar is excreted, but that insects penetrate the tissues for it. So I expect it must be with many foreign species. I forgot to say that if you find that you cannot fertilize any of your exotics, take pollen from some allied form, and it is quite probable that will succeed. Will you have the kindness to look occasionally at your bee ophrys near Torquay, and see whether pollinia are ever removed. It is my greatest puzzle. Please read what I have said on it, and on O. arachnites. I have since proved that the account of the latter is correct. I wish I could have given you better information.

My dear sir,

Yours sincerely,

CHARLES DARWIN.

P.S.—If the flowers of the Stanhopea are not too old, remove pollen masses from their pedicels, and stick them with a little liquid pure gum to the stigmatic cavity. After the case of the Acropera, no one can dare positively say that they would not act.