Date of Award

1980

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Abstract

The ontogeny and ultrastructure of the evergreen leaf of Magnolia grandiflora L. were studied by light microscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray microanalysis. The mature evergreen leaf was also compared with those of six deciduous Magnolia species. The vegetative apex of M. grandiflora can be described using the tunica-corpus and cytohistological zonation concepts. The apex is composed of a biseriate or triseriate tunica overlying a corpus and varies from 180 (mu)m at the minimal stage to 201 (mu)m at the maximal stage. Leaf primordia are initiated by periclinal divisions in the second layer of the tunica when the previous leaf primodium is 250-350 (mu)m in height. Following leaf initiation, a foliar buttress is formed. Marginal growth begins as soon as the buttress is formed with the leaf base gradually extending around the apex through periclinal divisions (in the second layer of the tunica) on both sides of the flank. The leaf primordium increases in height through apical growth which continues through the time the primordium is 1 mm in height. The leaf blade primordium is separated from the stipule by intensified anticlinal divisions in the surface and subsurface layers near the base. The leaf blade and the stipules continue development following their delimitation. Marginal growth begins in the leaf blade primordium when it reaches approximatly 200 (mu)m in height and results in the formation of the lamina. The young blade remains in a conduplicately folded position next to the stipule until bud break. Upon emergence of the leaf from the bud, the leaf rapidly increases in size by cell division and cell expansion finally to reach a mature size of 190-230 mm. Secretory oil cells are initiated in the leaves of M. grandiflora when the leaf blade is approximately 35 mm in length. An oil cell is initiated by an anticlinal division in the ground meristem of the leaf blade. The initial is identified from other ground meristem cells by its larger size, lower level of vacuolation, fewer starch grains and lack of osmiophilic bodies. Following initiation the oil cell increases in size by cellular expansion and eventually occupies a position in the mesophyll of the mature leaf. No evidence of lysigenous development, suberization or cupule formation was found in these cells. Silica is found in the leaves of M. grandiflora in the lumen of some of the terminal tracheids, vein sheath cells, epidermal cells and guard cells. Silica is also found external to the cell walls of epidermal cells and in the cuticle. The silica is amorphous and is composed of spherical silica bodies 35-65 nm in size. The mature evergreen leaf of M. grandiflora differs from deciduous Magnolia species in greater laminal thickness, larger number of cell layers, greater cuticle thickness, more sclerification, silicification, palisade mesophyll development, and absence of armed parenchyma.

Pages

191

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