The Collaborative International Dictionary of English v.0.48:

dendrology \den*drol"o*gy\, n. [Gr. de`ndron tree + -logy: cf.
   F. dendrologie.]
   1. the branch of botany studying trees and shrubs; the
      natural history of trees.
      [PJC]

   2. A discourse or treatise on trees.
      [1913 Webster] -- den`dro*log"ic*al, a. --
      den`dro*log"ic, a. -- den*drol"o*gist, a.
      [PJC]