PRELIMINARY-OBSERVATIONS ON THE STRUCTURE AND ORNAMENTATION OF THE OOSPORANGIAL WALL IN CHARA (CHARALES, CHLOROPHYTA)

The fertilization of the oosphere in the order Charales results in the formation of an oosporangium whose highly resistant outer organic wall is frequently decorated or ornamented. Examination by the scanning electron microscope allows for the unambiguous interpretation of such surface features and reveals details of wall structure and ornamentation not described hitherto. In this study of the oosporangia of 28 species of Chara the interpretations of the earlier light microscope investigations are reassessed and the following basic types of wall structure are recognized: a more or less continuous surface although pits, pores, and depressions are evident at c. x 15, 000; three-dimensional network of irregularly fused strands; perforate, with the larger pores often more than 0T pm in diam. Surface projections include low mounds, papillae, and perforated or unperforated pustules and granules. Often observed on acid-cleaned oosporangia are ribbon-like structures lying over and partly obscuring the region of wall lying between the spiral ridges or striae. Such structures arise on the spiral ridges and each normally consists of a thin wall bearing on either side fused nodular elements; the form and arrangement of these nodular elements sometimes differs between taxa. The taxonomic significance of characters provided by the newly described features of the oosporangial wall is assessed. © 1990 Taylor & Francis Group, LLC.