Plants grow upward from a tip of undifferentiated tissue called the shoot apical meristem. As the tip extends, stem cells at the center of the meristem divide and increase in numbers and the cells on the periphery differentiate to form plant organs, such as leaves and flowers. In between these two layers, a group of boundary cells go into a quiescent state and form a barrier that not only separates stem cells from differentiating cells, but eventually forms the borders that separate the plant’s organs. 

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