As a botanist, his work is denoted by the author abbreviation Thoday when citing a botanical name.
His nomination readsProfessor of Botany in the University College of North Wales, Bangor.
Distinguished for researches in plant physiology and causal anatomy, in which he has carried out work over a wide field.
In his earlier work he made important contributions to our knowledge of photosynthesis and respiration.
His later work has dealt with growth and differentiation in Compositae, and more especially with succulent members of this family, as exemplified in particular by 'Kleina articulata'.