In lemnaceous plants the iron-deficiency caused chlorosis and poor growth, showing the increase in number of connected fronds. Moreover, the formation of anthocyan and resting fronds were accompanied especially in Spirodela polyrhiza. Oxalates both in the form soluble and insoluble accumulated, when the culture solution was deficient in iron or nitrogen. However, the amount of the accumulating oxalate decreased secondary as the result of pathlogical condition of the piant body, when the deficiency in those elements became extreme. Lemnaceous plants utilized nitrates and ammonium salts as the nitrogen source, but in the latter case, especially when salts of strong acids were used, the plants wereharmfullyaffectedbytheincreasedphysiologicalacidityanddiedatlast. Nitrites and urea were also tolerably well available. The lowest pH-value of the culture solution which permits the existence of the plants was about 3.8.This pH-value, however could be further lowered to 3.2-3.4, if CaCl2 (0.001-0.01mol) was added to the culture solution as antagonist against hydrogen ion.The similar effect could be recognized also in MgCl2 or Al2K2 (SO4) 2. The resting fronds of the lemnaceous plants does not bud directly after its formation, even if the surrounding condition is regulated in favour of the growth. In the natural vegetation the resting fronds is awoke in early winter, probably by the in fluence of low temperature. The dormancy could be artificially removed by the treatment with 3% sodium sulphocyanate for 1-2hours, 0.1% heteroauxin for 2 hours, or 95% alcohol 1-2 hours.