The Collaborative International Dictionary of English v.0.48:

Boll \Boll\, v. i. [imp. & p. p. Bolled.]
   To form a boll or seed vessel; to go to seed.
   [1913 Webster]

         The barley was in the ear, and the flax was bolled.
                                                  --Ex. ix. 31.
   [1913 Webster]

Easton's 1897 Bible Dictionary:

Bolled
   (Ex. 9:31), meaning "swollen or podded for seed," was adopted in
   the Authorized Version from the version of Coverdale (1535). The
   Revised Version has in the margin "was in bloom," which is the
   more probable rendering of the Hebrew word. It is the fact that
   in Egypt when barley is in ear (about February) flax is
   blossoming.