Artifacts in video measurements cause growth curves to advance in steps

Abstract

Measurement of video recordings of mushroom growth seemed to reveal a stepwise mode of stipe elongation in fruit bodies of Caprinus cinereus and Agaricus bisporus in which brief episodes of explosive growth were followed by quiescent periods which could last many minutes. Similar stepped growth curves were obtained for hyphal extension growth in agar cultures. The stepped nature of these growth curves proved to be an artifact, probably caused by the fact that the video image is composed of a defined number of lines, phosphor dots and/or pixels. An essay test to verify the reality of any discontinuities in such observations is to make video records at a range of magnifications. If the steps (or other discontinuities) are real their absolute magnitude will be unchanged by the altered magnification (though the precision of the measurement will increase). If the steps are artifacts, their apparent absolute magnitude will decline at higher magnifications because the line interval in the image corresponds to a smaller absolute distance on the subject.