You take two plants that look very similar, have similar gro…

You take two plants that look very similar, have similar growing patterns, and flower at the same time, and place them in a greenhouse hoping they will cross-pollinate. However after three weeks of observation, you notice that you still don’t have hybrid seeds being produced. Which of these reproductive isolation mechanisms is most likely the culprit? 

You take two plants that look very similar, have similar gro…

You take two plants that look very similar, have similar growing patterns, and flower at the same time, and place them in a greenhouse hoping they will cross-pollinate. However after three weeks of observation, you notice that you still don’t have hybrid seeds being produced. Which of these reproductive isolation mechanisms is most likely the culprit?