The membranes of Lycopodium clavatum spores and Pinus silvestris pollen grains are similar, and have been found to consist approximately of cellulose (10—15%), an ill-defined “xylan” fraction (10%), a lipid fraction (55—65%) which on oxidative degradation gives a mixture of non-branched mono- and di-carboxylic acids with 16 carbon atoms or less, and a lignin-like fraction estimated to be 10—15%. The significance of these results is discussed.