His contribution to the field of plant biochemistry was substantial. Since his first publication in 1959, he produced over 100 research papers and more than 20 reviews. As Head of Plant Sciences he continued to maintain an active research group, training graduate students and producing a steady flow of research publications.
Soon after coming to Cambridge in 1965, he collaborated with members of the Biochemistry, Genetics and Zoology Departments to design and establish an important new course for first-year students which became known as Biology of Cells. This development was of enormous significance for science education at Cambridge and has been used since as a model for inter-disciplinary courses throughout the country. A whole generation of Cambridge chemists and physicists was enticed into careers in molecular and cellular biology after receiving from Tom ap Rees their first instruction in the mysteries of life.
He was born in 1930 and attended Llandovery College, Dyfed. In 1951, after two years' military service in the Royal Corps of Signals, he went up to Lincoln College, Oxford, where he was awarded an Upper Second in Botany. He stayed in Oxford for his DPhil, working with Dr J.L. Hartley in the Botany Department. Eighteen months' post-doctoral work at Purdue University in Indiana was followed by an antipodean migration to take up a lectureship in the Botany Department at the University of Sydney.
In 1961, still in Sydney, he moved on to the Plant Physiology Unit of CSIRO (Commonwealth Scientific and Industrial Research Organisation) where he became a Senior Research Officer. His globetrotting ended in 1964 when he returned to Britain to become a lecturer in the Botany Department at Cambridge University. In 1991 he was promoted to Reader, but never took up the post as it was overtaken by his election to the Chair of Botany.
In the wider scientific community he was a member of the Science and Engineering Board of the BBSRC (Biotechnology and Biological Sciences Research Council) and a formidable Chairman of the Plant and Microbial Sciences Board.
Ap Rees's commitment to education was absolute. He was an authoritative lecturer and a firm believer in the importance of practical work in the education of a scientist. Among his students he commanded respect and admiration through his natural authority and the excellence of his teaching. He became a Fellow and College Lecturer in Gonville and Caius College in 1965 and remained a dominant influence in the teaching of biology at Caius until he took up the Chair of Botany in 1991. In 1983 he was awarded the ScD from Cambridge University in recognition of his achievements in research. Between 1986 and 1991 he was a formidable Director of Studies in Biology, once describing his duties as "encouraging the faint-hearted and putting the fear of God into the idle".
Tom ap Rees was not your "typical" don: though he lunched in college almost daily he rarely dined or attended official College Feasts. But he never missed a Matriculation or Graduation Dinner, or other function at which students were entertained. He had precious gifts of gentle humour and the ability to instill self-confidence into his neighbours, whoever they were.
He had prodigious energy and led strictly by example: as Head of Department he gave his full share of lectures - and sat on more than his fair share of committees. He maintained an active group of graduate students and thus he could (and did) respond to grumbles about workloads with a robust "when you are doing as many lectures and sitting on as many committees as I am then you can complain". He summarised his management philosophy as a desire to create a sense of unity and "to be as much use to people as I can".
This policy governed his day-to-day approach to university life: he could always find time to help, whether you were a junior undergraduate or a senior member of staff. (Or even a historian colleague with a gardening problem.) The mystery was how he combined this open-door policy with getting so much done; in part he achieved it by being satisfied with the broad over-view: sometimes the details needed further attention, but the result was generally right.
To a certain extent, ap Rees kept his professional and personal life separate, though he took piles of work home and frequently entertained students there. Lunch, with his wife Wendy, started with a tour of the fine garden, and continued in a gallery of photographs of mountains. Gardens and mountains were the passions of his private life, his copious knowledge about them contributed to a grand view of all things natural.
His enthusiasm for gardens was useful when he was the acting Director of the Cambridge Botanic Garden (1995-96). He was also a proud son of Wales, a rugby enthusiast who somehow remained an optimist, and maintained close links with the Principality throughout his life.
This rich mix of talents and interests was often concealed by his natural modesty. One of us came back in the spring of this year from Gregynog in central Wales, enthusing about the beauty of the gardens, but surprised that the season was 2-3 weeks behind cold Cambridge. "That's because it's 692 feet above sea-level" was the reply: it turned out that for years ap Rees had been informally advising the gardens' Warden.
Thomas ap Rees, botanist and plant scientist: born Frome, Somerset 19 October 1930; Lecturer in Botany, Cambridge University 1964-91; Fellow, Gonville and Caius College, Cambridge 1965-91, Professor of Botany and Head of Department of Plant Sciences 1991-96; married 1955 Wendy Holroyde (three sons); died near Cambridge 3 October 1996.