The Collaborative International Dictionary of English v.0.48:

Perula \Per"u*la\, n.; pl. Perul[ae]. [L., dim. of pera
   wallet, Gr. ?: cf. F. p['e]rule.]
   1. (Bot.) One of the scales of a leaf bud.
      [1913 Webster]

   2. (Bot.) A pouchlike portion of the perianth in certain
      orchides.
      [1913 Webster]