Elizabeth Ewing's obituary by John R. Lee can be found here: (right click, open link in new tab) https://archive.org/stream/glasgowna141519401946ande/glasgowna141519401946ande_djvu.txt
Cullen was the Director of the Stanley Smith (UK) Horticultural Trust.
He trained at the University of Liverpool before coming to Edinburgh where he worked at the University's Department of Botany, at which point he assisted Peter H. Davis with his Flora of Turkey. Cullen then became Assistant Keeper at RBGE and editor of the European Garden Flora.
(info from (right click, open in new tab) http://assets.cambridge.org/052184/5068/frontmatter/0521845068_frontmatter.htm )
Charles C. V. Batts, Mycologist, National Institute of Agricultural Botany, Cambridge, 1951 - 1956.
Lecturer in Plant Pathology, Imperial College of Science, London, 1956 - 1960