Cytology of Conifers

III. Partial failure of meiotic spindle in Cephalotaxus drupacea var. pedunculata

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In Cephalotaxus drupacea var. pedunculata a case of partial failure of spindle during both divisions of meiosis in pollen mother cells has been re-corded. A wide variety of distribution has been observed at M.I, A.I, and AM. The chromosomes are scattered at all phases because of the lack of a directive influence of the spindle. Since there is no correlation between these arrangements at different stages it is concluded that many of these are supurious being caused by smearing per se. The chromosome division takes place normally in absence of a spindle and 48 chromatids are seen at the end of the meiosis. There are no other abnormalities.
Inspite of this abnormality there is a tendency of forming two nuclei at telophase I and four at telophase II. Tetrads are produced upto 46.7% and the rest constitute monads, diads (equal or unequal) triads and polyads containing upto 10 microspores. As expected all the cell walls are not laid by cell plate but there is evidence that wall formation takes place by furrowing.
Since normal and abnormal trees grow side by side it is concluded that the cause of the abnormality is genic rather than environmental. Furthermore, it may be said that such a genic control of spindle expresses itself under certain internal environmental conditions because both normal and abnormal cells are found within the same microsporangium. In this sense it appears that the genic control is not completely dominant.