Fig 20-2. Effect of photoperiod. The contrast between the rest period and photo period requirements of Howard 17 (left) and of Missionary (right) is shown by these plants brought into the greenhouse November 7 and held until March 10 during the short days of winter. Howard 17 does well in the North after a long winter cold rest period and thirteen- to fourteen-hour daylight periods at the time growth starts, while Missionary succeeds in Florida where there is a very short rest period and the daylight periods are about 10 hours when they blossom and fruit.