THE FINE STRUCTURE OF DIFFERENTIATING SIEVE TUBE ELEMENTS

Abstract

Cases of "distributive c-mitosis" (the term does not mean that colchicine has been used) in plant endosperm are described, in which the chromosomes of metaphase type (2 chromatid chromosomes) are distributed at random because of phragmoplast activity in a process similar to non-disjunction. There is some evidence that chromosmal fibers can be formed within the phragmoplast under special circumstances; during "distributive c-mitosis" some kinetochores show active movements due to cooperation with chromosomal fibers formed in the phragmoplast; while other chromosomes, as indicated by their arrangements and shape, are moved without any activity of kinetochores. Some components of the phragmoplast have the fastest movements occurring in mitosis. Some cases are described in which the phragmoplast divides telophase and interphase nuclei into 2 or more groups and moves the pieces a considerable distance apart. In a similar way, the phragmoplast may divide newly formed restitution nuclei. This phenomenon leads to a reduction of chromosome numbers, and the course of the process itself is reminiscent of amitosis.