A. macrogynus synthesized trehalose but apparently did not metabolize it. Trehalose was released to the suspending medium before the development of zoosporangia by plants suspended in water and before the development of resistant sporangia by plants in glutamic acid and glucose solution. Plants in the latter solution accumulated high levels of glycogen and trehalose before mRNA was transcribed for the development of resistant sporangia. Before the transcription of mRNA for either zoosporangia or resistant sporangia there was a period during which the plant content of glycogen, trehalose, protein and nucleic acid was constant. The increase in wall glycans and chitin during the development of zoosporangia was measured and possible origins of the walls are discussed.