Botanique.org

Xylem cells are the following:

 vessels or tracheids. Vessels are told perfect when there is no transverse wall and when all elements are joined together to reach a length that can reach many meters. Tracheids are imperfect vessels because they have a transverse wall with a lumen more or less important. Tracheids are present in basal(ADJ.) 1. SE DIT DE TOUT PHENOMENE AYANT SON SIEGE A LA BASE D’UN ORGANE. EN PARTICULIER, LA PLACENTATION EST DITE BASALE QUAND LES OVULES SONT SUR DES PLACENTAS DISPOSES A LA BASE DE L’OVAIRE. 2. EN CLADISTIQUE, SE DIT DES TAXONS PRIMITIFS AU SENS STRICT DU TERME, C’EST-A-DIRE APPARUS AVANT LES AUTRES ET AYANT DES CARACTERES PLESIOMORPHIQUES. (primitive) vascular plants such as Ferns and allies, or Gymnosperms.