Structure,function, and development of the peristome of the moss,Rhacopilum tomentosum,with special reference to the problem of microfibril orientation by microtubules

Summary The movement of the outer peristome teeth of the sporangium of the moss,Rhacopilum tomentosum, is driven by different swelling velocities of the outer (plates) and inner (ridges) wall thickenings due to suberin-like substances and wax-lamellae which enclose the ridges. The plates do not contain suberin-like material. The hydrophobic materials are secreted with the participation of smooth tubular ER.—When the local wall thickenings of the peristome teeth are formed, microtubules are concentrated along the plasmalemma in the thickening regions. They run along the crest of the developing plates (i.e., normal to the long axis of the tooth) and parallel to the long axis in the ridge cells. The wall thickenings are composed of layers of parallel microfibrils and of matrix substances. With a few exceptions microtubules and microfibrils have different directions. Golgi vesicles, subsurface ER and coated regions in the plasmalemma also are involved in cell wall formation. The function of the microtubules is discussed.