I hear with delight that you are meditating a trip to America, and I write forthwith to express my own and Mrs. Gray’s and my good father-in-law’s earnest hope that you will come over, even if it be for a few weeks only. The rest of the voyage cannot but be useful to so busy a person as you constantly are, and a run through the country, and a sight of the Yankee world, would interest you. At the Montreal scientific meeting you would see several old friends and many new ones. Torrey, Greene, Darlington,[34] James,[35] etc., would be half frantic with pleasure at the thought of seeing you; so it will not do to hint at such a thing, until you give me authority; and as for my wife and me, we will look after you like dutiful children, will go with you to Niagara, or to Lake Superior, if you will go so far, for there is nothing would give us so much pleasure as a visit from you; and if you would bring Lady Hooker or Mrs. Evans, or both, with you, it would be charming. The voyage is nothing to speak of, traveling here is easy and rapid, although not so very comfortable, as in England, and a good deal of the country can be seen in a few weeks without much fatigue. Pray do come, and exceedingly gratify, Your affectionate and faithful A. GRAY. TO JAMES D. DANA. December 13, 1856. MY DEAR DANA,--I duly received the sheets I asked for. The right way to bring a series of pretty interesting general questions towards settlement is perhaps in hand (though I do not expect myself to bring anything important to bear on it), viz., for a number of totally independent naturalists, of widely different pursuits and antecedents, to environ it on all sides, work towards a common centre, but each to work perfectly independently. Such men as Darwin, Dr. Hooker, De Candolle, Agassiz, and myself,--most of them with no theory they are bound to support,--ought only to bring out some good results. And the less each one is influenced by the other’s mode of viewing things the better. For my part, in respect to the bearings of the distribution of plants, etc., I am determined to know no theory, but to see what the facts tend to show, when fairly treated. On the subject of species, their nature, distribution, what system in natural history is, etc., certain inferences are slowly settling themselves in my mind, or taking shape; but on some of the most vexed questions I have as yet no opinion whatever, and no very strong bias, thanks, partly, to the fact that I can think of and investigate such matters only now and then, and in a very desultory way. I cannot say that I believe in centres of radiation for groups of species. From Darwin’s questions to me I think I perceive some of the grounds on which he would maintain it. One is attended to on page 77 of the January number [of “Silliman’s Journal”], but I am not clear that they are not just as susceptible of other interpretation.