Apocynaceae V: Seasonal variation in chromosome association and male sterility in a single floweringTabernaemontana divaricata

A single-flowering, male sterile variety ofTabernaemontana divaricata (2n=22) had a high frequency of univalents. Observations on material fixed at nine periods during the year showed univalent frequency to be negatively correlated with temperature. Chromosome association was normal only at temperatures around 40°C. As pollen sterility did not vary with temperature, it was concluded that it had developmental-genetic rather than meiotic causes.