The earliest published record of diurnal changes in sap acidity appears to be the report of Heyne (8) in 1813 who detected it by the sense of taste. He found that Bryophyllum calycinum was more sour early in the morning than in late afternoon. According to Richards (19), these observations were corroborated by Link who tested the juice from the same species and other crassulaceous forms with litmus paper. Other investigators also verified these observations and various explanations were offered for such diurnal changes in acidity (6, 21). Succulents were used in most of the early investigations on diurnal changes in sap acidity and the acidity there of was measured as measured was total titratable acidity. Gustafson (6) recorded diurnal changes in total and actual acidity of the juice of Bryophyllum calycinum, and found the lowest pH at 4 P.M. on a sunny day. The hydrogen-ion concentration underwent a similar series of changes on cloudy days, the chief difference being that changes were more pronounced on sunny days. Gustafson reported pH 3.90 for 10:00 A. M. and pH 5.37 for 4 P. M. for whole tops of Bryophyllum calycinum. Ingalls and Shive (13) recorded pH values 3.44 and 4.93 at 9 A.M. and 5 P.M., respectively, for stems, and pH 3.34 and 4.92 at 7 A.M. and 5 P.M. for leaves of Bryophyllum.
Proceedings of the Iowa Academy of Science
©1953 Iowa Academy of Science, Inc.
Loehwing, Helen C.
"Diurnal Changes in Sap Acidity of Certain Plants,"
Proceedings of the Iowa Academy of Science, 60(1), 192-199.
Available at: https://scholarworks.uni.edu/pias/vol60/iss1/25