An attempt was made to develop a true breeding strain of white double-flowered Portulaca grandiflora Hook. White double-flowered plants of two strains were bred to the second generation using single plant selections. Both single- and double-coloured flowers were introduced into the breeding programme to gain information on the breeding behaviour of flower doubleness and colour. Seed dormancy and the failure of the plants to grow in the greenhouse during the winter months resulted in prolonging the breeding programme. Methods of overcoming these delays were investigated. The results obtained from these investigations and the breeding studies are briefly as follows. Genotypically a true breeding strain of white double-flowered portulaca can be obtained but environment and somatic mutations so influence the phenotype that few, if any, of the plants are considered desirable. Multiple alleles apparently exist for colours from red to magenta and because of the small numbers of plants grown it was impossible to determine the breeding behaviour of this group. The dormant period of portulaca seed can be shortened by pre-germination chilling of the seed, soaking them in a weak solution of potassium nitrate and then germinating at alternating temperatures. Normal plant growth can be maintained throughout the winter in the greenhouse if additional light and heat are supplied to the plants. / Land and Food Systems, Faculty of / Graduate