Reference pollen slides have been made from twenty-three samples of material identified as Tilia platyphyllos Scop., T. cordata Mill., or T. × vulgaris Hayne. Up to 100 grains in each slide have been microscopically examined and each opposing face has been classified as of ‘cordata’ or ‘platyphyllos’ type. The survey showed that grains of T. platyphyllos material were homopolar and consistently of ‘platyphyllos’ pattern. Some material of T. cordata was also homopolar and consistently of ‘cordata’ pattern. There was, however, an extreme degree of heteropolarity in most of the hybrid material and also in much of that attributed to T. cordata, a large proportion of the grains having ‘cordata’ pattern on one face and ‘platyphyllos’ on the other.
The results show the extreme importance of adequate authentication of pollen type-material and suggest that in Britain both T. cordata and T. platyphyllos are native, but that much hybridization has occurred between them, giving progeny in which the somatic phenotypes show less indication of ‘platyphyllos’ parentage than the pollen seems to do.