Pectins are predominant in the middle lamella, the layer between neighbouring cells.
Depending on the dominant sugar is it spoken of xylans, galactanes, or of arabinogalactans , for example, if both sugars occur in nearly equal amounts. The delimination between the two classes is fluid. They were based both on the choice of suitable test objects and on the use of sensitive analytical techniques. Moreover do they secrete polysaccharides into the media, the composition of which resembles that of wall polysaccharides. A little time ago was it proven that certain oligosaccharides set free by the wall have specific regulatory functions.