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Ragweed pith
Primary pit fields
Primary pit fields
Wall, face view
Nucleate cells
Compact parenchyma
Sclerenchyma
Intercellular spaces
Leaf, xs
Chlorenchyma
Shoot tip, ls
Apical meristem
Vascular cambium
Secretory duct
Resin canal
Clusia duct
Root cortex
Leaf aerenchyma
Air chambers
Air chambers
Aerenchyma, Acorus
Stellate cells
Epidermis
Endodermis
Phloem, ls
Phloem, xs
Transfer cells
Bean cotyledon
Acorn, starch
Potato starch
Ice plant cell
Tannin cell
Small cells

Fig. 3.7-1. Longitudinal section of the shoot apical meristem of Coleus. The shoot apical meristem produces all the cells of the shoot, and the root apical meristem produces all those of the root. Thus most cells start out as small, more or less cuboidal cells not much larger than a nucleus, then the cells grow to their mature size and shape. The larger cells at the bottom center of the micrograph will develop into very large pith parenchyma cells, and prominent intercellular spaces will form as the cells round up and push slightly apart from each other. The cells along the surface of the meristem will differentiate into epidermis cells, secreting cutin to their outer, exposed side (Fig. 3.4-1). Some meristem cells will develop as elongate sieve tube members (Fig. 3.5-1) or fibers, and some cells might develop “arms” like those of cattails (Fig. 3.3-6). It is important to remember that as long as the cells are growing, the primary walls can be pushed into some unusual shapes, but they cannot pulled back – plant cells are not as free to change shape as animal cells are.