The Collaborative International Dictionary of English v.0.48:

Protonema \Pro`to*ne"ma\, n.; pl. Protonemata. [NL., fr. Gr. ?
   first + ?, ?, a thread.] (Bot.)
   The primary growth from the spore of a moss, usually
   consisting of branching confervoid filaments, on any part of
   which stem and leaf buds may be developed.
   [1913 Webster]