A fibrillar structure formed in the cytoplasm from microtubules at the commencement of * metaphase. When present, * centrioles move so they are diametrically opposite each other on the disintegrating nuclear membrane. In the majority of plant cells, where there are no centrioles, poles still become established at opposite points. The fibrils radiate from each pole towards the centre or equator. The attached microtubules direct the chromatids (or chromosomes in the first meiotic division) towards opposite poles. Evidence tends to support the view that this is achieved by the microtubules becoming progressively shortened as a result of depolymerization in the regions nearest to the poles. |
