Figure 5-6a. Blackberry flower bud. The larger bud (primary bud) on the left has a brown center that was killed by temperatures below 27°F. The smaller bud at the center (secondary bud) was not injured by the cold and will produce flowers and fruit. The brown nub on the right is a remnant of the leaf from the previous summer.
Cross-section of blackberry flower bud with brown center which was killed by freeze

Source: Gina Fernandez.