For a primary callus culture, most convenient are tissueswith high contents of parenchyma or meristematic cells. In such explants, mostlyonly a limited number of cell types occur, and so a higher histological homogeneityFig. 1.2 Various techniques of plant cell and tissue cultures, some examples: top left callus culture,top right cell suspension culture, bottom left protoplast culture, bottom right anther cultureexists than in the entire organ. However, growth induced after transfer of theexplants to the nutrient medium usually results in an unorganized mass or clump ofcells—a callus—consisting largely of cells different from those in the originalexplant.