The growth of Avicennia marina was recorded in nutrient culture to which a range of concentrations of sodium chloride, potassium chloride, and calcium chloride were added. All levels of potassium chloride and calcium chloride suppressed growth, but a positive growth response to sodium chloride was recorded. The optimum level of sodium chloride was approximately 1?V2 per cent, which is half of the concentration in sea water. THE TERM MANGROVE is applied to a group of floristically diverse trees and shrubs which characterize the coastal vegetation of many tropical and subtropical areas. A feature of the mangrove habitat is the high salinity, and much has been speculated, less written, and little experimental effort expended, on the physiological relationship between mangroves and salinity. One question relates to the possible essentiality of sodium as a nutrient for these species; another to the degree and basis of tolerance exhibited toward high concentrations of sodium in the field. It is notoriously difficult to conclude anything of the physiological response of plants from observation of their field distribution (Ellenberg 1952), and it would appear that culture experiments with mangroves are long overdue. With the exception of the work of Stern and Voigt (1959) there are no repeatable, controlled experimental data on the response of mangroves to culture conditions generally, or salinity in particular. In that work it was shown that Rhizophora mangle L. responded to the inclusion of sea-water2 in the nutrient culture and that, moreover, within the limits of the range of treatments applied, maximum growth was achieved at salt concentrations equivalent to sea water. The present work deals with the grey mangrove [Avicennia marina (Forsk.) Vierh. var. resinifera (Forst.) Bakh.I and its response in culture to a range of concentration of various salts. The goals of the present investigation were: the ecological status of the plant and preliminary data on the physiology of its salt tolerance. METHODS The experiments were performed in a glasshouse at Brisbane, Australia (lat. 27.5?S), during the spring of 1967. A non-aerated nutrient culture system was used in which levels were adjusted each day with deionized water and entire solutions changed at 10-day intervals. The containers were glazed earthenware pots of two-litre capacity into which sets of three plants were suspended through holes in thick, black nylon covers. The basic nutrient was a modified Hoagland's (Hewitt 1966), and its composition is given in table 1. It was, however, never used at full strength during the course of the experiment. The dilutions are described later along with the planting details. Mature fruits were collected from trees growing in the Pine River Estuary, 10 miles north of Brisbane on August 20. Fruits of even size were selected and set out to germinate on the following day on TABLE 1. Composition of the basic nutrient solution (all concentrations relate to the element). MacronuMicronutrients trients (Hoagland's Conc. (Hoagland's Conc. No. 1) (#M/1) No. 2) (ppm) N as (NO3)15,000 Fe 2