Morphological characteristics of the resting nuclei and chromosomes observed in 115 species of 52 genera of Orchidaceae were summarized, and the following five types of nuclei were found in Orchidaceae. Diffuse type: Characterized by the dark staining chromatins without conspicuous aggregation, and associated with the large chromosomes without any particular heterochromatic segment. Simple chromocenter type: Characterized by the light staining chromatins and some dark staining chromocenters with rough surface, and has no connection with chromosome size; some of the chromosomes of the complement have a gradual heterochromatic segment at the proximal region. Complex chromocenter type: Characterized by many dark staining chromocenters which vary in shape and aggregate into several large chromatin blocks, and associated with either medium or small chromosomes; most of the chromosomes of the complement have several gradual heterochromatic segments at proximal as well as interstitial and distal regions. Rod prochromosome type: Characterized by the smooth-faced rod prochromosomes, and associated with small chromosomes; most of the chromosomes of the complement have a clearly distinguishable heterochromatic rod segment at the proximal region. Round prochromosome type: Characterized by the smooth-faced round prochromosomes, and associated with small chromosomes; most of the chromosomes of the complement have a clearly distinguishable heterochromatic round segment at the proximal region.