(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.
The boll of a plant is its seed-vessel or pod. Cf. Fitzherbert, 'The bolles of flaxe