Mason was born on September 23, 1928, near Winsted, Connecticut, and grew up on the family farm there, where he developed an interest in natural history. When he entered Yale University in 1946, he intended to study languages, but was told by the faculty that only graduate students could study Sanskrit and other ancient languages. Disappointed, he turned instead to biology, where his choice of botany over zoology was made more or less randomly. It brought him under the influence of Alexander W. Evans, with whom he began his training on lichens. Mason received a BS degree in botany (honors) from Yale and was elected to Phi Beta Kappa in 1950.

Mason continued his studies of lichens with John W. Thomson at the University of Wisconsin. His PhD dissertation was an ecological analysis of the corticolous lichens of southern Wisconsin that made use of ordination techniques being developed at that time by John Curtis and colleagues. He received the PhD degree in 1953 and taught briefly at the University of Wichita from 1953 to 1955 and West Virginia University from 1955 to 1957 before coming to the Smithsonian Institution as an associate curator in the Department of Botany.

Mason spent 33 years at the Smithsonian, two of them as departmental chair from 1968 to 1969. He oversaw a fivefold expansion of the lichen collection, which made it the largest in the United States and probably third largest in the world; Mason personally collected approximately a third of the specimens in the collection. Mason’s collecting took him to every continent and brought to the Smithsonian over 80,000 specimens. He was perhaps proudest of his trips to Antarctica (1980-85), where he studied the endolithic lichens of the dry valleys. These most unusual organisms live inside the porous rocks there and can be collected only by cracking rocks to expose the lichens inside.

Mason published nearly 200 scholarly works, including five books and numerous lengthy monographs. The Biology of Lichens (1967, 1974, 1983) introduced a generation of students to lichens; similarly, How to Know the Lichens (1969, 1979) became the standard identification manual for North America. He was co-editor of The Lichens (1973) and co-author of Lichens of California (1988).

Mason’s research covered all areas of lichenology. Early in his career at West Virginia University, with the physiologist V. G. Lilly, he did numerous experiments that investigated the nutritional requirements of lichen fungi. He was an early advocate of the use of chemical characters in the interpretation of evolutionary trends in lichens. He made extensive use of the scanning electron microscope, producing in over 15 years a library of microscope negatives that will prove invaluable to future researchers. His photographic studies of lichen growth in the eastern United States had application in both ecology and environmental studies.

In 1961, Mason was elected to membership in the Washington Biologists’ Field Club. He was an active participant in all Club activities, serving frequently as outdoor cook at the annual shad bake and oyster roast. He was most interested in continuing the lichen work begun on the island by founding member William Maxon and members Emery Leonard and Ellsworth Killip. This began as survey work, but developed into an extensive biomonitoring effort involving the use of lichens as environmental indicators of air quality.

The most significant of these efforts began in 1959 and measured lichen growth rates photographically at permanent sites established across the island. Done over a period of nearly 20 years, these measurements established correlations between lichen growth and various microclimatic factors, which were recorded continuously with the assistance of his son Robert. When the Capital Beltway Bridge (now the American Legion Memorial Bridge) was completed in 1965, the environment of the island changed considerably, and Mason was able to observe marked changes in lichen responses. Later studies with Club member Jim Lawrey demonstrated significant uptake of various heavy metals and other pollutant elements by lichens on the island. Since lichens have been collected on the island for over 100 years, analysis of collected lichens provided retrospective data about the island’s environment in the past. In addition, measurements have been collected up until the present. Due to Mason’s efforts, the Club has an extensive set of environmental data for the island that begins in the 1890s and continues into the present.

Mason was stricken with renal cell cancer in 1989 and died at his home in Arlington, Virginia, on April 23, 1990. Although he was not technically among those members eligible to have memorial plaques mounted on the island after death, the Club asked for and received permission from the National Park Service to place a commemorative plaque on the island for Mason. At his family’s request, his ashes were also placed on the island. At the memorial service on the island dedicating Mason’s plaque, his family members noted his fondness for the Club and his excitement over his research projects conducted on the island. Since his death, lichenologists visiting Washington from foreign countries frequently ask to see the island where he worked and the plaque mounted there in his honor.