Some of the nodal roots of field-grown Zea mays L. bear a persistent soil sheath along their entire length underground except for a glistening white soil-free zone which extends approximately 25 mm behind the root cap. These roots are generally unbranched. The histology of the surface and the rhizosphere of the sheathed roots has been examined by correlated light and electron microscopy. All mature peripheral tissues including root hairs, are largely intact and apparently alive where enclosed by the soil sheath. The sheath is permeated by extracellular mucilage which is histochemically distinct from the mucilage at the epidermal surface, but similar to that produced by the root cap. Isolated cells resembling those sloughed from the sides of the root cap persist in the soil sheath along the length of these roots. Fresh whole mounts of the sheath show that these detached cells may be alive and streaming vigorously even at some distance from the root cap. Rhizosphere mucilage is associated with the isolated cells.
Floral apices of Chrysanthemum morifolium cv. Dramatic form glandular trichomes on the receptacle in interfloret positions and on the corolla tube above the constriction subtended by the ovary. The glandular trichomes in both positions are initiated by the enlargement of single epidermal cells followed by a single anticlinal division and a series of periclinal divisions resulting in a 10-celled biseriate structure. Receptacular trichomes develop while florets are being initiated on the flanks of the floral apex and by the time petal primordia are initiated these trichomes are mature. Glandular trichomes on the corolla tube are initiated on peripheral florets while florets are still being initiated in a centripetal direction. Each glandular trichome has a cuticular covering beneath which secreted materials accumulate, thereby distending the cuticle. A large pore eventually forms in the cuticle and presumably allows the escape of secreted substances.
Glandular trichomes on the inflorescence of Chrysanthemum morifolium cv. Dramatic are initiated from a single epidermal cell outgrowth and develop through an anticlinal division and a series of periclinal divisions to form a biseriate multicellular structure. Cells of the young trichome contain a large nucleus with prominent nucleoli and few small cellular organelles. Prior to the secretory stage, numerous ribosomes, polyribosomes, and dictyosomes are present in a dense cytoplasm but most of the dictyosomes are lost as secretion commences. Plastids in the stalk cells senesce but in a different manner than those in the upper tiers of secretory cells. Lipoidal substances form in the degenerating plastids. Cell wall ingrowths and the deposition of a flocculent material in the primary cell wall characterize secretory hairs. In very old hairs cellular lysis takes place with mitochondria being the last cellular organelle to remain intact. The secreted material, which collects in a subcuticular space, appears to be a terpenoid. The function of this material is not known.
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