1. Brennan, E. G., Plant Physiol. 25: 736 (1950).
2. Applegate, H. G., Phyton, Ann. rei botan. 14: 111 (1960).
3. Adams D. F. paper to be presented at the annual meeting of the Air Pollution Control Association New York June (1961).
4. Air Pollution Handbook 1956
5. Applegate H. G. unpublished information (1960).