Olsen, Sigurd and Ingrith D. Olsen. "Photography for the Preservice Biology Teacher." The American Biology Teacher 38/2 (February 1976): 88-90, 109.

Olsen, Sigurd and Ingrith D. Olsen. "Photography for the Preservice Biology Teacher." The American Biology Teacher 38/2 (February 1976): 88-90, 109.