The Collaborative International Dictionary of English v.0.48:

Resting \Rest"ing\,
   a. & n. from Rest, v. t. & i.
   [1913 Webster]

   Resting spore (Bot.), a spore in certain orders of algae,
      which remains quiescent, retaining its vitality, for long
      periods of time. --C. E. Bessey.
      [1913 Webster]

WordNet (r) 3.0 (2006):

resting spore
    n 1: a spore of certain algae or fungi that lies dormant; may
         germinate after a prolonged period