Summary: Relative phytotoxicity of purified, biodegradable surfactants was determined by observing their effects on the growth of orchid seedlings in vitro. Pronounced phytotoxic effects occurred on culture media containing high concentrations of surfactants. Concentration of ionies above 100 ppm were most damaging and also caused a 90% or greater reduction of interfacial tension. Nonionic ethoxylates reduced growth and viability at lower concentrations than ionies, but larger percentages of seedlings survived at 1000 ppm levels of these agents, which were less efficient in reducing interfacial tension. No correlation was found between biological effects and surface tension data but a coincidence may exist between interfacial tension reduction by ethoxylates and increased phytotoxicity. A number of purification procedures for surface active agents are presented as an Appendix.

Summary: Effects of a nonionic surface active agent (lauroyl/myristoyl di (2‐hydroxyethyl) amide) and one anionic surfactant (sodium (linear) dodecylbenzene sulphonate) on cell ultrastructure were determined using Phalaenopsis protocorms. There were no observable effects after 5 days exposure to 1000 ppm of the nonionic. However, the anionic caused severe damage. Drastic changes in morphology, loss of membranes, swelling of thylakoids and appearance of dense osmophilic granules were evident in chloroplasts. Other effects include disintegration of polysomes into monosomes; swelling of mitochondria; dispersion of chromatin in the nucleus; appearance of unidentified vesicles in the cytoplasm and plasmolysis of cells. These ultra‐structural changes can be attributed to the possible emulsification of membrane lipids as well as precipitation and dispersion of cellular proteins.