STUDIES ON THE SPOROGENOUS LINEAGE IN THE MOSS TIMMIELLA-BARBULOIDES .7. THE MICROTUBULE ARRAYS AT MEIOSIS

This correlated immunofluorescence and electron microscope study revea ls that the microtubule arrays during meiosis in Timmiella barbuloides mirror those in other mosses but the organization of the metaphase I spindle is quite different. In other mosses the sagittiform metaphase I spindle initially contains four bands of microtubules derived from t he tetrahedral system present at prophase. These bands converge toward s the division axis and each half spindle contains two focal points of microtubules straddling a cleavage furrow. In Timmiella the sagittifo rm spindle also contains four microtubular foci derived from the prepr ophasic tetrahedron. However, one of these contributes to one half spi ndle, the other half deriving from the three remaining foci orientated at approximately 120-degrees to each other. In contrast to other moss es the sporocytes in Timmiella are hardly lobed, the cleavage-furrows ill-defined, the prophasic plastid positioning in the lobes is also mo re variable and the organelle band in meiocytes comprises mitochondria alone.