In a previous paper ('33) the author reported the result of growing seedlings of Cattleya Trianae Linden & Rchb. f., on three-salt solutions of various ratios, all having a total osmotic concentration of one atmosphere. It was found that the best growth was associated with solutions having low concentrations of phosphate ions. All other ions were varied between wide limits with but little apparent effect. There is ample evidence in the literature of plant nutrition to support the belief that any set of nutrient salts at a given total concentration will exhibit more or less definite ratios for optimum growth, particularly if external conditions be kept constant. Since the effectiveness of any salt ratio depends upon the total concentration, it is not possible to compare the effects of specific ions in solutions differing in the total amount of salt present. The addition of extraneous ions may modify the permeability of the protoplasm and disturb the effectiveness of a given salt ratio. The solutions studied in the present work differ from each other in many respects, and the biological value of specific ions is therefore modified or obscured so that no comparison on the basis of ionic composition may be made. Such a comparison is possible only with the triangular series of salt ratios at a given total osmotic concentration. In the previous paper, the nutrient solution of La Garde ('29) was cited as a very favorable medium for the germination and growth of orchids, but its effectiveness could not be attributed to the specific concentrations of the potassium or phosphate ions. The present study was carried out to test this further, and to ascertain which of several published nutrient solutions were most satisfactory for the germination of orchid seedlings. The technique was the same as that described in the previous paper. The seeds were Cattleya Trianae Linden & Rchb. f. and from the same pod as those used for the triangular studies. The flasks were inoculated June 10, 1932, and the measurements were taken January 21, 1933. The molecular compositions of the solutions used are indicated in table i; their composition in parts