M. J. McMahon
Two chrysanthemum [Dendranthema x grandiflorum (Ramat) Kitamura] cultivars, 'Bright Golden Anne' and 'Spears' were grown in unfiltered sunlight (control) or under filters that removed far-red (FR) light under long- or short-day photoperiods for a total of four treatments per cultivar. Eight pinched plants from each cultivar were exposed to each treatment. Tips of lateral branches were harvested every three days and preserved in formalin, acetic acid, and 70% ethanol (5:5:90 v:v), then observed and photographed under a dissecting microscope.
In 'Spears,' all short-day treatments developed floral primordia at the same time, and the rate and development were normal. Under long days and FR-absorbing filters, floral primordia initiated and developed normally, but were delayed several days compared to short days. Plants under long days and control filters also developed normal promordia, but at a slower rate than the other treatments.
In 'Bright Golden Anne,' only short-day treatments developed normal floral primordia. Under long days, plants under FR-absorbing filters eventually initiated floral primordia but development was abnormal. No floral primoridia developed under long-day and control-filter conditions. In all cases, 'Spears' primordia development was much more rapid than 'Bright Golden Anne.'