JDH thanks Asa Gray for his opinion on an unspecified essay by JDH, letter includes discussion of species & specific centres suggesting the subject of the essay is geographical plant distribution, the definition of a species & whether they are created entities or varieties evolve with environmental influences. JDH refers Gray to his comments in the FLORA ANTARCTICA. He argues against Gray & Agassiz's belief in multiple centres. Discusses the relative importance of genetic resemblance as opposed to habitat, referring to the Dorking Fowl, Manx Cats & Falkland Island rabbits. He favours theories based on observable evidence of geography, physiology etc. Dismisses Agassiz's work, incl on glaciers such as Aletsch, as prejudice not based in fact but on a desire for notoriety. JDH & Lyell like Agassiz personally. JDH looks to Americans for future discoveries in science as he considers them more practical. Bentham has decided to give his herbarium to RBG Kew. Thomas Thomson [TT] wants to be botanist on an expedition to North West Australia, if the East India Company will give him leave. Hurt approves of TT, who was imprisoned with his brother during the Afghanistan campaign. William Jackson Hooker has applied to The Duke of Newcastle on TT's behalf. Writes of progress with FLORA INDICA & distribution of plant sets to Gray, Paris, Berlin, Vienna, St Petersburg, Brown at the British Museum, Lowell & Torrey. Asks Gray about North American Larch, Yew, Junipers & Coniferae incl. Scotch Pine. Uses Yews from Pontrilas as an example of the difficulty of using habitat vs character in determining species. The Deodar Avenue at Kew is another example of how plants may not always have the ideal characteristics of their species. Agrees that species cannot be pronounced the same because they are united by certain forms, gives Mt Lebanon & Himalayan Cedars as example of extreme forms. Argues the difficulty is with local botanists wanting to give local varieties a distinct classification.