In 1831, his finding at Killarney of the beautiful moss _Hookeria laetevirens_, hitherto unknown in Ireland, led to the formation of one of the warmest and most valuable friendships of his life. He forwarded specimens, with a characteristic letter, to W. J. Hooker at Glasgow, and the kind and encouraging reply which he received led to further letters and eventually to an intimacy which seems to have been prized equally on both sides. Hooker recognized at once the extraordinary talent of the shy young man of twenty, lent him books, asked him to visit him, and congratulated him on his critical faculty, predicting for him a rapid advance to "the top of algologists." Another life-long friendship made about this time was with Mrs Griffiths of Torquay; and he numbered Greville and Agardh among his earliest correspondents. Already he was deep in his life-task of comparing and describing plants, working with the restless energy which characterised him. "I rise at five every morning," he writes, "and work till breakfast, examining or describing the Algae for the 'British Flora[109].' If I do five species a day I think it good work. This may seem slow, but there is much to be compared and _corrected_! for I differ from Dr Hooker on many species. Oh, impudence! oh, presumption!" In 1832 he undertook to do the Algae for J. T. Mackay's _Flora Hibernica_, which was published three years later; this was his most important contribution to the botany of his native land. The death of his father in 1834 broke up Harvey's home life, and his strong desire to study the vegetation of distant countries led to enquiries as to the obtaining of an appointment in the Colonies. New South Wales was first thought of, but it was for the Cape that he started in the following year. Asa Gray, a friend of many years' standing, tells, in a notice of Harvey in the _American Journal of Science and Arts_[110], a curious story as to the circumstances attending this momentous change in Harvey's life. The story is repeated in the notice of Harvey in Seemann's _Journal of Botany_[111], though not mentioned in the _Memoir_ edited by his cousin. It seems that, as the result of Harvey's representations, he obtained through Mr Spring Rice, afterwards Lord Monteagle, the post of Treasurer at the Cape; but, by an accident, the appointment was made out in the name of an elder brother (Joseph Harvey); and an inopportune change of ministry occurring just at the time, frustrated all attempts at rectification. Be that as it may, Joseph Harvey sailed for South Africa in July 1835, taking his younger brother with him as assistant.