1. An area within the microfibrils of a cell wall, about 50 nm in length, where the cellulose chains lie very closely parallel to each other. The resulting orderly organization of the cellobiose units (see cellulose
) results in a very regular arrangement of atoms in these areas so that the cellulose is essentially crystalline.
2. A clay-humus particle that is formed when finely divided mull humus complexes with the clay particles in the soil. It is negatively charged and thus various positive ions are absorbed on its surface. These may be exchanged for other positive ions and the total amount of ions held in this way is termed the exchange capacity of the soil.