Interphase chromosomes in meristematic cells look static in their outward appearance. However, in actual fact, synthesis of DNA, RNA, and other substances preparing for the subsequential nuclear division are actively performed in interphase cells. Morphological study of metabolic nuclei dates from the 1920s. Based on differences in chromatin condensation, as detected by a simple dye-staining technique, E. Heitz suggested the concept of euchromatin and heterochromatin. Thus there is no doubt that the field of morphological study on metabolic phase leave many curious subjects to be investigated, since those new visualizing techniques make it possible to observe the unknown phenomena visible during the metabolic stage. The aceto-orcein squash method has greatly contributed to the study of plant chromosomes, although its popularity decreased after the 1970s with the advance of numerous chromosome-banding techniques. However, aceto-orcein staining is commonly used for the analysis of karyotypes in many species and for observing condensation in metabolic and prophase chromosomes.