"Wheat grows three times a day, and Hsinchu becomes a tall bamboo overnight" is an image description of the rapid growth of wheat and bamboo stems. What kind of meristem is this rapid growth?

A. Mesenchymal meristem is distributed between differentiated and mature tissue areas, and usually refers to primary meristem derived from apical meristem and left in some local areas of some organs. The jointing of monocotyledonous plants such as wheat and bamboo, and the continuous harvesting of leeks are all due to the activities of mesophyll, which is in line with the meaning of the question.

B. The stems of herbaceous plants include epidermis, parenchyma cells and vascular bundles, in which vascular bundles are composed of phloem and xylem, without cambium. Wheat and bamboo belong to herbaceous plants, and there is no cambium in the vascular bundle of the stem, so it cannot be thickened indefinitely.

C apical meristem is located at the top of roots, stems and branches at all levels, including primary meristem and its derived primary meristem, which can make roots and shoot tips grow primarily, which does not meet the meaning of the question.

D, root tip meristem is surrounded by root cap and belongs to meristem, with small cells, thin cell wall, large nucleus and thick cytoplasm. The ability to divide is strong, and it can constantly divide to produce new cells, replenish root caps downwards and transform them into elongation zones upwards, which has nothing to do with the rapid growth and height of stems.

So choose: a