APA (7th ed.) Citation

Darwin, C. (1939). Calendar of the Letters of Charles Robert Darwin to Asa Gray. The Historical Records Survey.

Chicago Style (17th ed.) Citation

Darwin, Charles. Calendar of the Letters of Charles Robert Darwin to Asa Gray. Boston, Mass.: The Historical Records Survey, 1939.

MLA (8th ed.) Citation

Darwin, Charles. Calendar of the Letters of Charles Robert Darwin to Asa Gray. The Historical Records Survey, 1939.

Warning: These citations may not always be 100% accurate.