Marguerite Gertrud Anna Henrici, plant physiologist, spent some time in France after completing her schooling and in 1913 entered the University of Basle to study botany, chemistry and zoology. She later specialized in plant physiology and was awarded a doctoral degree by the same university in 1917. After some time as assistant to Professor G. Senn she became a researcher in the university's botanical institute during 1920-1922. Here she was recruited by Arnold Theiler* to join his team at the Onderstepoort Veterinary Research Institute in research on lamsiekte.
Arriving in South Africa in November 1922, her brief was to study the seasonal variations of phosphate, a deficiency of which had been shown to cause the disease, in the vegetation of affected areas. For this purpose she was stationed at, and put in charge of, the Armoedsvlakte experimental farm in the Vryburg district. This project developed into a life-long study of the food value of South African grasses and veld types, resulting in some 80 scientific papers during her career. Her first paper based on work performed in South Africa, written in German, dealt with the transpiration of grasses and was published in a Swiss journal in 1923. This was followed by several further papers on the chlorophyll, carbohydrate and phosphorous content of grasses, and the cystine and sulphur content of Karoo shrubs, in the 11th and 12th Report of the Director of Veterinary Education and Research between 1926 and 1928. Two more general papers, both published in the South African Journal of Science, dealt with "Growth of veld plants under arid conditions of Bechuanaland" (1926) and "Grass or bush in the Karroid area?" (1931). In 1927 the University of South Africa awarded her a DSc degree for a thesis titled Studies in plant physiology in South Africa and Europe.
From July 1926 to December 1927 Henrici was stationed at the Ermelo Research Station to study the phosphorous content of highveld grasses. The results were published in two papers in the 16th Report of the Director of Veterinary Services in 1930. Meanwhile she had been transferred in 1929 from the Veterinary Division to the Division of Plant Industry of the Department of Agriculture, under I.B. Pole Evans*. A veld reserve was established at Fauresmith in the Free State and a field station built there for a study of the Karoo vegetation. Here she spent almost 30 years in fruitful research and published many papers in the South African Journal of Science, the Science Bulletin of the Department of Agriculture, and Farming in South Africa. Considering her language problems - she initially spoke German, French and a little English - and the fact that few women were appointed to professional posts at the time, she adapted well to the mainly Afrikaans speaking farming community.
After spending the year 1939 on vacation in Europe Henrici conducted an important series of experiments on transpiration in grasses, Karoo bushes and other vegetation, leading to several publications. However, her techniques elicited some criticism and divergent opinions on the relative effects of indigenous and exotic trees on ground water resources involved her in some controversy. After reaching retirement age in 1948 she continued her work at Fauresmith in a temporary capacity until March 1957. After her final retirement she stayed in the town for many more years and in 1968 the local farming community honoured her with an illuminated address. Poor health eventually forced her to enter a home for the aged in Bloemfontein, where she died two years later.
Henrici became a member of the South African Association for the Advancement of Science in 1926 and was president of its Section C in 1937. Also in 1926 she joined the South African Biological Society and was awarded its Senior Captain Scott Memorial Medal in 1935. She was an honorary member of the Basle Botanical Society and in 1969 received an honorary doctorate from her alma mater, the University of Basel. In 1971 she was made an Honorary Life Member of the South African Association of Botanists. She accumulated a herbarium of over 6000 specimens, mainly from the western Free State and Ermelo. These are housed in the National Botanical Institute in Pretoria and in the herbarium of the McGregor Museum, Kimberley, while a set was kept at the veld reserve at Fauresmith. The plant genus Neohenricia was named after her by H.M.L. Bolus*, and the species Salsola henriciae by I. Verdoorn.
