Another viewpoint on Perthro:
The Old English Rune Poem reads "[ Lot box ] is always play and laughter among bold men, where warriors sit in the beer hall, happily together." Neither the Old Norwegian Rune Poem nor the Icelandic Rune poem address the Rune. Consequently it is often interpreted as the Rune of Chance, Gambling, and Luck.
However, I was studying Runelore, by Edred Thorsson, in preparation for a Rune Talk workshop. More specifically I was hand copying the list he provides in the Appendix (see p. 204-205) for the Anglo-Friesian Futhork, and I noticed the similarity in the drawings, and alternate drawings, of Runes numbered 14, 21, and 32, scratched below:
When I noticed that the shape of the Frisian drawn stave for Rune 14 Perthro, and Rune 21 for Lagu, water, was the same, I realized that in olden times Perthro probably stood for the Well of the Norns, or Urdr's Well located in Asgard where the Aesir meet at their lawgiving. This would give the Rune Perthro its current interpretation of chance, luck, and mystery, but what was lost was the Rune's original connection with the Well of the Norns. If this was indeed the original interpretation, the meaning could have been lost along with the traditional practice of women's mysteries, which were probably associated with the mystery of the womb and childbirth, around the time of the Romans conquests when the influx, migration, and intermingling of peoples disrupted old customs and introduced new ones. I have included Anglo-Frisian Rune 32 because of the similarity of the shape and the fact that the Rune's name, Stan, means Stone.
Quote from the Younger Edda, "...the norns, that dwell in the fountain of Urd, every day take water from the fountain and take the clay that lies around the fountain and sprinkle therewith the ash, in order that its branches may not wither or decay. This water is so holy that all things that are put into the fountain become as white as the film of an egg-shell. As is here said: An ash I know/Hight Yggdrasil;/A high, holy tree/ With white clay sprinkled./Thence come the dews/That fall in the dales./Green forever it stands/Over Urd's fountain. The dew which falls on the earth from this tree men call honey-fall, and it is the food of bees. Two birds are fed in Urd's fountain; they are called swans, and they are the parents of the race of swans." (Snorri, Chapter VII, V. 16
This passage from Snorri's Younger Edda supports my idea when I consider that the Rune itself looks like a cup, pot, or can turned on its side to pour or release water. The connection to Stan/Stone seems equally obvious to me because earth contains water. Earth and water are two elements that mingle in order to provide the chemistry necessary to life.
Water also provides a metaphor for the changing states of the Soul, and the presence of the swans at Urd's Well are a clue to the involvement of the Valkyries that ride to choose the slain for Valhalla. Only those who had lived lawfully would be chosen for that high estate - another clue given by the presence of Urd's Well is by the Thing and that the Norns are responsible for overseeing Ørlög, the Norse word most akin to karma, fate, destiny.