The Collaborative International Dictionary of English v.0.48:

Gang-flower \Gang"-flow`er\, n. (Bot.)
   The common English milkwort (Polygala vulgaris), so called
   from blossoming in gang week. --Dr. Prior.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Milkwort \Milk"wort`\, n. (Bot.)
   A genus of plants (Polygala) of many species. The common
   European Polygala vulgaris was supposed to have the power
   of producing a flow of milk in nurses.
   [1913 Webster]

   Note: The species of Campanula, or bellflower, are
         sometimes called milkwort, from their juice.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rogation \Ro*ga"tion\, n. [L. rogatio, fr. rogare, rogatum, to
   ask, beg, supplicate: cf. F. rogation. Cf. Abrogate,
   Arrogant, Probogue.]
   1. (Rom. Antiq.) The demand, by the consuls or tribunes, of a
      law to be passed by the people; a proposed law or decree.
      [1913 Webster]

   2. (Eccl.) Litany; supplication.
      [1913 Webster]

            He perfecteth the rogations or litanies before in
            use.                                  --Hooker.
      [1913 Webster]

   Rogation days (Eccl.), the three days which immediately
      precede Ascension Day; -- so called as being days on
      which the people, walking in procession, sang litanies of
      special supplication.

   Rogation flower (Bot.), a European species of milkwort
      (Polygala vulgaris); -- so called from its former use
      for garlands in Rogation week. --Dr. Prior.

   Rogation week, the second week before Whitsunday, in which
      the Rogation days occur.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Polygala vulgaris
    n 1: small European perennial with numerous branches having
         racemes of blue, pink or white flowers; formerly reputed to
         promote human lactation [syn: common milkwort, gand
         flower, Polygala vulgaris]