The actual tree to which Polo refers in the text was probably one of those so frequent in Persia, to which age, position, or accident has attached a character of sanctity, and which are styled Dirakht-i-Fazl, Trees of Excellence or Grace, and often receive titles appropriate to Holy Persons.  Vows are made before them, and pieces torn from the clothes of the votaries are hung upon the branches or nailed to the trunks.  To a tree of such a character, imposing in decay, Lucan compares Pompey: 

    “Stat magni nominis umbra. 
  Qualis frugifero quercus sublimis in agro,
  Exuvias veteres populi sacrataque gestans
  Dona ducum * * * * *
  —­Quamvis primo nutet casura sub Euro,
  Tot circum silvae firmo se robore tollant,
  Sola tamen colitur.”
      (Pharsalia, I. 135.)

The Tree of Mamre was evidently precisely one of this class; and those who have crossed the Suez Desert before railway days will remember such a Dirakht-i-Fazl, an aged mimosa, a veritable Arbre Seul (could we accept that reading), that stood just half-way across the Desert, streaming with the exuviae veteres of Mecca Pilgrims.  The majority of such holy trees in Persia appear to be Plane-trees.  Admiration for the beauty of this tree seems to have occasionally risen into superstitious veneration from a very old date.  Herodotus relates that the Carians, after their defeat by the Persians on the Marsyas, rallied in the sacred grove of Plane-trees at Labranda.  And the same historian tells how, some years later, Xerxes on his march to Greece decorated a beautiful Chinar with golden ornaments.  Mr. Hamilton, in the same region, came on the remains of a giant of the species, which he thought might possibly be the very same.  Pliny rises to enthusiasm in speaking of some noble Plane-trees in Lycia and elsewhere.  Chardin describes one grand and sacred specimen, called King Hosain’s Chinar, and said to be more than 1000 years old, in a suburb of Ispahan, and another hung with amulets, rags, and tapers in a garden at Shiraz.[7] One sacred tree mentioned by the Persian geographer Hamd Allah as distinguishing the grave of a holy man at Bostam in Khorasan (the species is not named, at least by Ouseley, from whom I borrow this) comes into striking relation with the passage in our text.  The story went that it had been the staff of Mahomed; as such it had been transmitted through many generations, until it was finally deposited in the grave of Abu Abdallah Dasitani, where it struck root and put forth branches.  And it is explicitly called Dirakht-i-Khushk, i.e. literally L’ARBRE SEC.