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2. Concentric35.12 The position of the different types of cells inside the plant are also fixed. The dermal tissue is on the outside of both stem and shoot. The vascular tissue is found in the center of the root and at fixed location inside the stem and leaf. The ground tissue is located around the vascular tissue. Plants must have a mechanism that generates the appropriate type of cell in the appropriate position. D. Meristems35.13 1. Overview Unlike animals, plants are continually generating complete new organs (leaves for example). They are able to do this because plants contain undifferentiated, perpetually "embryonic" tissues known as meristems. 2. Asymmetric cell division Meristemic cells are self-regenerating stem cells; that is, when they divide, they produce one daughter that remains undifferentiated (called an initial) and one that differentiates (called a derivative)

Meristem Derivative

Meristem

Meristem initial

Meristem

Derivative

Derivative[!]mature structure

This is another example of asymmetric cell division. 3. Primary growth Primary growth results from cells generated by apical meristemsat the tips of roots and shoots. a. apical meristems[!]primary meristems35.15 The meristem is a clump of dividing cells which give rise to 3 types of cells arranged in concentric rings. These are known as primary meristemsbecause they continue to divide before differentiating into mature structures. The apical meristem at the tip of the root divides and generates the three primary meristems continually.