Yapp was appointed botanist to
Cambridge University's 1899–1900 expedition to the North-Eastern
Malay States, led by
Walter William Skeat. Specimens he collected on the expedition went to the Cambridge University Herbarium, with some in the National Collection at Kew. On his return to Cambridge, he was curator of the university's herbarium from 1900 to 1903, He was appointed Professor of Botany at
Aberystwyth University in 1904, adding to the university's museum collection specimens he collected in South Africa in 1905. He served on the central committee of the Study and Survey of British Vegetation, later renamed the British Vegetation Committee. This group evolved, in 1913, into the
British Ecological Society, In 1914, he became Chair of Botany at
Queen's University, Belfast. He was also assistant to Sir Arthur Yapp, his older brother, in the
Ministry of Food during
World War I. An adapted edition was also produced for Australian schools, in 1934. == Illness and death ==