ABSTRACT
Cytologists have devised cytological techniques from time to time to obtain precise information on chromosome numbers, chromosome structures, size and shape, and to examine the mechanism of cell division in plant species. These properties are studied by cytological techniques. The cytological procedures are modified depending upon the crop species, the objective of the experiments, available facilities, and, above all, the personal preference of the cytologists. Pretreatment of roots is an essential step for studying the mitotic chromosomes. It performs several purposes: it stops the formation of spindles, increases the number of metaphase cells by arresting the chromosomes at the metaphase plate, contracts the chromosome length with distinct constrictions, and increases the viscosity of the cytoplasm. Numerous pretreatment agents, described below, have been developed. Nitrous oxide, a gaseous substance, was found to induce chromosome doubling and has spindle inactivation effect like colchicine. The science of chromosome study depends upon good fixative.
