Page:First course in biology (IA firstcourseinbio00bailrich).pdf/95

 Upper figure is of moonseed:

c, cambium; d, ducts; 1, end of first year's growth; 2, end of second year's growth; bast part at left and wood part at right. Lower figure (from Wettstein) is sunflower: h, wood-cells; g, vessels; c, cambium; p, fundamental tissue or parenchyma; b, bast; bp, bast parenchyma; s, sieve-tubes.

why dicotyledonous bundles form rings of wood and monocotyledonous cannot (Figs. 75 and 76). The dicotyledonous bundle (Fig. 76) has, running across it, a layer of brick-shaped cells called cambium, which cells are a specialized form of the parenchyma cells and retain the power of growing and multiplying. The bundles containing cambium are called open bundles. There is no cambium in monocotyledonous bundles (Fig. 75) and the bundles are called closed bundles. Monocotyledonous stems soon cease to grow in diameter. The stem of a palm tree is almost