In 1900, Henry went to France to study at the French National School of Forestry at Nancy. He later became joint author with Henry John Elwes of the 7 volume "Trees of Great Britain and Ireland" 1907–13. His contribution here was unique insofar as he devised a system of identification based on leaves and twigs and on the position of buds to aid identification even in the absence of fruit and flowers. He was involved in the establishment of the Chair of Forestry at Cambridge University in 1907, and remained there until 1913. He was responsible, with A.C. Forbes, the Director of Forestry at the Department of Agriculture and Technical instruction, for the lay-out of plots of trees at Avondale, County Wicklow.