Ingenhousz in an elegant experiment with an aquatic plant showed that in bright sunlight, small bubbles were formed around the green parts while in the dark they were not. Later he identified these bubbles to be of __________

Conceptual,NCERT XI PAGE 207.

Jan Ingenhousz (1730-1799) showed that sunlight is essential to the plant process that somehow purifies the air fouled by burning candles or breathing animals.

 Ingenhousz, in an elegant experiment with an aquatic plant, hydrilla, showed that in bright sunlight, small bubbles were formed around the green parts while in the dark they did not. 

Later, he identified these bubbles to be of oxygen. Hence, he showed that it is only the green part of the plants that could release oxygen.