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 -7.5°C and an ice front is apparent. For subsequent images 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.