The assumption is made that photosynthesis evolved in prokaryotes and was acquired by symbiosis in all eukaryotes. By studies of comparative mitosis and genetic systems of "lower" eukaryotes (e.g., nucleate algae, protozoa, flagellated fungi and so forth) consistent phylogenies of these organisms may be constructed. It follows logically from these considerations that the traditional concept of "plant" and "animal" kingdoms are obsolete. An internally consistent modification of Whittakers five kingdoms (Monera, Protist, Fungi, Animal and Plant) is represented and defended on the basis of information from ultrastructure, comparative biochemistry and life cycles, molecular biology and other modern work. Higher taxa (Kingdoms, Phyla, Classes) for major groups based on the recognition of the prokaryotic-eukaryotic dichotomy is offered for critical evaluation.