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The pollen grain of pollen is generally made of only 2 haploid cells:

 The tube cell, responsible for the elongation of the pollen tube,
 The generative cell that will give 2 male gametes or sperm cells.

The pollen grain is surrounded with 2 walls:

 The exine(N. F.) ENVELOPPE EXTERIEURE DU GRAIN DE POLLEN. VOIR : SPORODERME., thick, ornamented or smooth,
 And the intine(N. F.) ENVELOPPE INTERNE DU GRAIN DE POLLEN. VOIR : SPORODERME., fine and doubling inside the exine.

In certain places called aperture(N. F.) OUVERTURE DANS L'ENVELOPPE DU GRAIN DE POLLEN (SPORODERME). CE PEUT ETRE UN PORE OU UN SILLON UTILISE LORS DE LA DEHISCENCE DU GRAIN DE POLLEN POUR LA SORTIE DU TUBE POLLINIQUE.s, exine is thinner and intine thicker. In the pollen of Monocots or Basal Dicots, there is normally only one aperture, circular or furrowed. Sometimes, this aperture stretches, being thinned by places it then gives several pores.

In the pollen of true Dicots (Eudicots), there are normally 3 apertures. However, this number can vary and be multiplied.