I am looking for the next two publications, published in the South African Journal of Agricultural Science, in 1968: • Oberholster, R.E. 1968a, A method for separation of plant opal in soils, South African Journal of Agricultural Science, 11 (1) : 195-196, en • Oberholster, R.E. 1968b, Opal phytolith in two soil profiles on the Springbok Flats. South African Journal of Agricultural Science, 11 (4): 743-748. Much appreciated Gerhard