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SUMMARY 1. The assimilation of inorganic nitrogen by Scopulariopsis brevicaulis and some physiologically similar species has been studied. Their failure to assimilate completely from ammonium sulphate has been shown to be due to the fall in pH of the medium induced by the initial uptake of ammonia. 2. Complete assimilation of ammonia takes place in the presence of the neutral salts of each of thirteen organic acids investigated. The organic acids act prima rily through their buffering effect which prevents or slows down the fall in pH. They are not specifically required for ammonia assimilation by these fungi and can be effectively replaced by certain inorganic buffers. 3. The influence of several external factors on the rate of assimilation of ammo nia, nitrate, and nitrite has been studied in S. brevicaulis. In corresponding condi tions the mycelium assimilates ammonia more rapidly than .nitrate over a wide range of conditions. 4. Ammonia, even in very low concentration, completely suppresses nitrate assimilation when both sources of nitrogen are present together. Nitrite, how ever, is assimilated simultaneously with ammonia. It is therefore concluded that ammonia blocks the reduction of nitrate to nitrite by the fungus. 5. The suppression of nitrate assimilation in the presence of ammonia is com mon to many mould fungi besides S. brevicaulis, and is believed to have adaptive significance in natural habitats. 6. The nitrate-reducing and assimilating system is formed, even when S. brevi caulis is grown in complete absence of nitrate (ammonia medium with organic acid). It comes into action rapidly when the inhibiting effect of ammonia is removed. Similarly, nitrate-grown mycelium is capable of assimilating ammonia at maximal rate without any adaptive lag.

SUMMARY Barley, Brussels sprout, French bean, tomato, and sugar-beet plants grown in soil in pots and sprayed, usually daily, for several weeks, with nutrient solutions containing nitrogen, phosphorus, potassium, and a spreader, with precautions to prevent the spray solution falling on the soil, had higher nutrient contents and dry weights than control plants sprayed with water and spreader only. Increase in nutrient content occurred with high or low levels of nutrient supply to the roots and was approximately proportional to the concentration of spray and to the frequency of spraying. The nitrogen content of sugar-beet plants was increased equally by spraying with solutions supplying ammonium sulphate, calcium nitrate, or urea in equiva lent concentrations. Nutrient uptake from solutions sprayed on leaves influenced uptake by the roots so that the additional amounts of nutrient contained in sprayed plants may be greater or smaller than the amount absorbed from the spray by the leaves.

SUMMARY Plants were grown in sand cultures to observe the effects of mineral deficiencies, with different sources of nitrogen supply, on leaf acid phosphatase activity using phenolphthalein phosphate as substrate. Large increases ranging from 7 to 18 times normal (on fresh weight or protein basis) occurred with deficiency of phosphorus with nitrate, nitrite or ammonia nitrogen ; increases from 4 to 8 times normal occurred with deficiencies of zinc with nitrite or ammonia; and of copper with nitrite. Less pronounced increases, from z to 3 times normal on a protein basis, occurred with deficiency of zinc with nitrate; of boron with all nitrogen sources; of manganese and of iron with nitrite. Activities on both protein and fresh-weight basis were often greater with nitrite or ammonium sulphate than with nitrate. Effects of phosphorus, zinc, copper, boron, and nitrogen sources were significant. Molybdenum deficiency caused approximately z times normal activity on a protein basis in tomato, tobacco, sunflower, cauliflower, lucerne, mustard, spinach beet, and lettuce when nitrate was given. Effects with ammonia nitrogen were not consistent in molybdenum-deficient plants but 50 per cent, increases occurred in the first 5 species listed. Activities varied widely between species. It was concluded that the increases in activity were caused by increases in amounts of the enzyme produced during growth, and that different combinations of deficiencies and nitrogen supplies produce different specific responses in terms of enzyme synthesis.