The Danish plant ecologist who assisted a Danish chemist, famous for the introduction of the concept of pH died in 1974.
Carsten Erik Olsen (March 1, 1891  August 19, 1974) was a Danish plant ecologist and plant physiologist, who pioneered the study of plant nutrition in soils of different pH. 
Sren Peder Lauritz Srensen (9 January 1868  12 February 1939) was a Danish chemist, famous for the introduction of the concept of pH, a scale for measuring acidity and alkalinity. 
