I hate to inform you but Ray Rogers was wrong. Pliny the Elder never said that Saponaria officinalis was used in the bleaching of linen. What he said is, “There is another kind of wild poppy (a spurge rather, Euphorbia esula of Linnaeus), known as "heraclion" by some persons, and as "aphron" by others. The leaves of it, when seen from a distance, have all the appearance of sparrows; the root lies on the surface of the ground, and the seed has exactly the colour of foam. This plant is used for the purpose of bleaching linen cloths in summer.” — Pliny the Elder, The Natural Histories, Book 20, Chap.79
The heraclion plant is not Struthium (soapwort, Saponaria officinalis).
It was Theophrastus who said that struthium was used for bleaching linen. Pliny, according to some sources, misunderstood Theophrastus to mean heraclion.
Was Saponaria officinalis used for bleaching linen 2000 years ago? Yes. Do we need to correct about a million web pages at this point? Probably.
It is a bit curious where Rogers got his information.
For your reading pleasure: Pliny the Elder: the Natural History