Plant tissue consisting of undifferentiated cells where active cell divison occurs. The meristematic tissue is an area of active plant growth. Undifferentiated cells divide and form new, specialized cells. Meristematic tissue may be the cambium layer, leaf or flower buds, shoot tips, or root tips.
Gallmaking insects oviposit or feed on their host plants during periods of growth. A gallmaking wasp, for example, may lay eggs just as leaves are opening or shoots are lengthening. By interacting with the plant's meristematic tissue, the insect takes advantage of a period of active cell division to initiate the formation of a gall by the plant.