The Collaborative International Dictionary of English v.0.48:

Lignify \Lig"ni*fy\ (l[i^]g"n[i^]*f[imac]), v. t. [imp. & p. p.
   Lignified (l[i^]g"n[i^]*f[imac]d); p. pr. & vb. n.
   Lignifying (l[i^]g"n[i^]*f[imac]`[i^]ng).] [L. lignum wood
   + -fy: cf. F. lignifier.] (Bot.)
   To convert into wood or into a ligneous substance.
   [1913 Webster]