OVULE DEVELOPMENT INORNITHOGALUM CAUDATUM(LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION

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Abstract
SUMMARY: The chalazal end of the egg projects beyond the synergids while the micropylar end is in contact with the nucellar epidermis. The egg nucleus and nucleolus are large and, along with most of the cytoplasm, are located chalazally while a large vacuole occupies the micropylar end. The egg cell wall is attenuated chalazally but, based on preliminary light microscope observations, it does appear to surround the entire cell in some cases. The synergids each have a large chalazal vacuole with the majority of their cytoplasm in the micropylar half of the cell. Nuclei and nucleoli are large and other organelles are numerous. Plastids and endoplasmic reticulum (ER) are more numerous chalazally while mitochondria appear to be evenly distributed. Filiform apparatus (FA) formation occurs late in synergid maturation. The FA is large, well developed, and is surrounded by a vacuolate zone. Various sized vesicles with fibrillar or flocculent contents occur within the FA. The FA stains for both protein and RNA in addition to carbohydrate which is the dominant component. The synergid walls have a knobbed ingrowth around the periphery of their micropylar end. Neither egg nor synergids store any metabolites.This information, coupled with overwhelming evidence from the literature reviewed, has led me to conclude all angiosperm synergids are active in synthesizing and, via the FA, in secreting a substance(s) which influences the final phases of pollen tube growth. Movement of materials into a megagametophyte via the FA seems unlikely, but if it does occur, it is probably an inconsistent feature and only of trivial consequence.