Biology 1st Edition by Jerome Krueger, Kendra Hill, Robert Noyd

تمرين 5

Poinsettias are beautiful houseplants that are commonly sold between Thanksgiving and Christmas ( Fig. ). The poinsettia initiates flowering when it has sustained six weeks of nights that were longer than 11.5 hours (critical day length of 12.5 hours). Is it a short-day or a long-day plant? In the United States, do poinsettias enter their photoperiod around the vernal equinox (March 20-21) or the autumnal equinox (September 22-23)? Name an animal that is attracted to the poinsettia's red "leaves."
Figure Poinsettia flowers.