Light microscopy of the unicellular green alga Cylindocystis brebissoni during cooling at a rate of 1°C per minute in the cryoprotective additive dimethylsuphoxide. This image was taken at -20°C. The cells have partitioned into the freeze concentrated solution, which has decreased in size. For a subsequent image click on Next. At this rate of cooling extensive cellular shrinkage is observed, intracellular ice is not apparent, and the recovery on thawing was high.