Breakdown of fat in watermelon seedlings germinated in the dark occurs in essentially the same way as in the light. Free fatty acids do not accumulate and the composition of the lipid remains almost unchanged during its rapid utilization. The low weight of ‘protoplasmic lipid’ remaining in the etiolated cotyledons after the storage fat has disappeared contains a lower proportion of linolenic acid than that from green cotyledons of a corresponding age. The weight of phos phatide (lipid P) per cotyledon increases both in light- and dark-grown seedlings until 8 days, thereafter declining in the dark but continuing to rise in the light. Phosphatide and glyceride fractions from the same fat resemble each other fairly closely in fatty acid composition.