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(4), where large losses of nitrogen were observed with Chlorella and with Narcissus leaves floated on nutrient solutions. DAVIDSON'S (2) experiments with wheat and cowpeas, where no losses were observed, illustrate the (b) type of experimentation.The results of Pearsall and Billimoria are so striking that a brief summary of their experiments is profitable. In their comparatively few experiments with Chlorella, the organisms were grown in a heavily buffered phosphate medium (pH6) containing 1 per cent. glucose and approximately 13 mg. of nitrogen as NaNO3 per 50 ml. of nutrient solution. After incubation for 28 days in darkness, nearly two-thirds of the added nitrogen had disappeared; after 11 days in the light the loss was 6 per cent.In their more extensive work with Narcissus, sterilized leaves were floated on nutrient solutions containing various forms of nitrogen, glucose, and phosphates to buffer the solution at pH 5.4. Different portions of old and young leaves were incubated in the culture media in both light and darkness. No losses were observed where organic sources of nitrogen were 496 www.plantphysiol.org on May 12, 2018 -Published by Downloaded from

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