Cytogenetics of Polyploids

IV. Cytology of photoperiodic races and cytotypes of Ageratum conyzoides L

抄録

The paper gives an account of the cytological features of two cytotypes (diploid and tetraploid) and of two ecological races viz., monsoon and winter form, both being tetraploids. The winter form is characterized by a higher number of metacentric chromosomes and higher recombination index; the range of chromosome length being similar in both the forms. Significant reduction in chiasmata from diplotene to diakinesis occurs in both the forms but the chiasma frequency differs significantly between the two forms being higher in winter form. Prefixatives and climatic factors seems to affect the chisama relationships of bivalents significantly. Resemblance in karyotype, morphology and in habitat preference between diploid and winter forms leads one to believe the former to be a putative parent of the latter form. But this needs confirmations.