Abstract
The development of the spindle body was studied in the spore mother cells of Equisetum arvense under the electron microscope. The spindle body consists of two elements, spindle fibers and a spindle matrix filling the spaces between these spindle fibers. These spindle fibers originate from the cytoplasm as follows. Microtubules of 25mμ in diameter become visible among the cytoplasmic organelles (such as mitochondria and plastids) in early diakinesis (Fig. 2). These microtubules move to the cytoplasmic region around the nucleus (Figs. 3-6) during diakinesis, while other organelles such as mitochondria and plastids move to the periphery of the cell (forming the clear zone). As soon as the continuous nuclear envelope breaks into fragments (prometaphase-I), these microtubules intrude into the nuclear area from the clear zone together with ER, small vesicles (30-100mμ in diameter) and cytoplasmic matrix (Figs. 7 and 8). They may connect with the kinetochore of each chromosome (chromosomal fibers, Fig. 9). Some microtubules not connected with kinetochore may form continuous fibers running from pole to pole (Figs. 9 and 10).
