Max Frei/Courtesy Alan Whanger

Grain by grain. To confirm his identification of this pollen grain pulled from the shroud (left), Max Frei compared it to a control grain of Gundelia tournefortii (right). Mounted in glycerin to prevent the delicate grains from being squished between the glass slides, the individual pollen grains were studied using a light microscope and compared to other, known grains to identify their genus and species. Frei determined that this grain—as well as numerous others from the shroud—was Gundelia tournefortii, which is found only in parts of the Near East. The authors of Flora of the Shroud of Turin, though unable to confirm all of Frei’s findings owing to the deterioration of the original samples, concluded that there were 91 grains of Gundelia tournefortii on the tapes.