Complex sentence: In 1841, W.J. Hooker became director of Kew and Fitch moved to London and after 1841 Fitch was the sole artist for all official and unofficial publications issued by Kew.
Split into simpler sentences: In 1841, W.J. Hooker became director of Kew and Fitch moved to London. After 1841 Fitch was the sole artist for all official and unofficial publications issued by Kew.