Abstract

Barbara McClintock won the Nobel Prize in 1983 for her discovery of mobile genetic elements. Her Nobel work began in 1944, and by 1950 McClintock began presenting her work on "controlling elements." McClintock performed her studies through the use of controlled breeding experiments with known mutant stocks, and read the action of controlling elements (transposons) in visible patterns of pigment and starch distribution. She taught close colleagues to "read" the patterns in her maize kernels, "seeing" pigment and starch genes turning on and off. McClintock illustrated her talks and papers on controlling elements or transposons with photographs of the spotted and streaked maize kernels which were both her evidence and the key to her explanations. Transposon action could be read in the patterns by the initiated, but those without step by step instruction by McClintock or experience in maize often found her presentations confusing. The photographs she displayed became both McClintock's means of communication, and a barrier to successful presentation of her results. The photographs also had a second and more subtle effect. As images of patterns arrived at through growth and development of the kernel, they highlight what McClintock believed to be the developmental consequences of transposition, which in McClintock's view was her central contribution, over the mechanism of transposition, for which she was eventually recognized by others. Scientific activities are extremely visual, both at the sites of investigation and in communication through drawings, photographs, and movies. Those visual messages deserve greater scrutiny by historians of science.