SECRETION AND DEPLOYMENT OF BRISTLES IN MALLOMONAS SPLENDENS (SYNUROPHYCEAE)1

Mallomonas splendens (G. S. West) Playfair has a cell covering of siliceous scales and bristles. Interphase cells bear four anterior and four posterior bristles that each articulate, at their flexed basal ends via a complex of labile fibers (the fibrillar complex), on a specialized body scale (a base-plate scale). Body scales, base-plate scales and bristles are formed independently of each other and at different times in silica deposition vesicles (SDVs) that are associated with one of the two chloroplasts. The fine structure of scale and bristle morphogenesis in M. splendens agrees with that previously described for Synura and Mallomonas. Four new posterior bristles are formed at late interphase with their basal ends towards the cell posterior. The fibrillar complex is formed in situ on the bristle in the SDV. Mature bristles are secreted one by one onto the surface of the protoplast, beneath the layer of body scales, where the basal ends of the bristles adhere to the plasma membrane via the fibrillar complex. The extrusion of posterior bristles and their deployment onto the cell surface was monitored with video. A fine cellular protuberance accompanies the bristles as they are extruded from beneath the scale layer with their basal ends leading. When distant from the cell, the basal ends of the bristles appear attached to the protuberance, possibly by way of their fibrillar complexes. Once bristles are fully extruded, and their tips free in the surrounding environment, the bristle bases are drawn back to the posterior apex of the cell, apparently by the now shortening protuberance. Thus a 180° reorientation of the posterior bristles has been effected outside the cell. Thin-sections of cells that are extruding bristles show a threadlike, cytoplasmic extension of the cell posterior which may be analogous to the protuberance seen in live cells. Four new posterior base-plate scales are secreted after the bristles have reoriented. Scanning electron microscopy indicates that the fibrillar complex is involved in positioning the bristles onto their respective base-plate scales. Anterior bristles are formed in new daughter cells in the same orientation as the posterior bristles; thus they are extruded tip first and no reorientation is required.     

STUDIES ON ULTRASTRUCTURE AND THREE‐GENE PHYLOGENY OF THE GENUS MALLOMONAS (SYNUROPHYCEAE)1

The genus Mallomonas, a common and often abundant member of the planktic community in many freshwater habitats worldwide, consists of 180 species divided into 19 sections and 23 series. Classification of species is based largely on ultrastructural characteristics of the siliceous scales and bristles that collectively form a highly organized covering over the cell. However, the relative importance of the different siliceous features of the scales, such as the dome, V rib, and secondary structures, as well as the different types of scales, in understanding the evolution and phylogeny of the genus is little known. In this study, we investigated the scale and bristle ultrastructure, along with sequences of three genes, for 19 isolates (18 species) of Mallomonas (18 isolates were from Korean habitats). The isolates represented nine of the 19 sections. Sequences for both the nuclear SSU and LSU rDNA and plastid LSU of RUBISCO (rbcL) genes for each of the 19 Mallomonas isolates and four outgroups were determined. Bayesian and maximum‐likelihood (ML) analyses of the data revealed that Mallomonas consists of two strongly supported clades. Mallomonas bangladeshica (E. Takah. et T. Hayak.) Siver et A. P. Wolfe was at the base of the first clade that included taxa from the sections Planae and Heterospinae, both of which lack a V rib on the shield of the scales. Our results indicated that the sections Planae and Heterospinae should be combined. The second clade, with Mallomonas insignis Penard and Mallomonas punctifera Korshikov at the base, contained taxa from the sections Mallomonas, Striatae, Akrokomae, Annulatae, Torquatae, Punctiferae, and Insignes, all of which have V ribs or well‐developed marginal ribs on the scales. Sister relationships between Mallomonas and Striatae were strongly supported, but interrelations among the remaining sections were not resolved, probably due to inclusion of too few species. Our results suggest that the current classification of the genus Mallomonas at the section level will require some revision. Additional species will need to be added in future analyses.     

A STATISTICAL CHARACTERIZATION OF GROWTH AMONG CLONES OF SYNURA PETERSENII (SYNUROPHYCEAE)1

Each of four clones from the Synura petersenii complex was grown at different pHs (5.5, 6.5, 7.5, 8.5) in batch culture experiments. Growth response curves and exponential growth rates were compared among clones and pH treatments in order to examine growth trend variation among the clonal groups. The clones were isolated from geographically distant North American localities. The clonal groups represented distinct mating types, an isolate and its subisolate, and S. petersenii- and S. glabra-like scale morphologies. No consistent relationship existed between growth response curve, and culture medium pH. Additionally, the trends across time differed according to clone and pH combination. Pairwise comparisons of linear trends from transformed growth response curves indicated two distinct clonal associations. Although the clonal associations corresponded with the final cell density of the cultures, growth response curves did not correspond with mating type, the parent-isolate and subisolate, or scale morphology. Clones with glabra-like scales had greater growth rates than the clone with petersenii-like scales. The conflicting results generated from growth response curve and growth rate analyses support the concept that S. petersenii and S. glabra form a highly variable, homogeneous grouping.     

SEASONAL PERIODICITY OF CHRYSOPHYCEAE AND SYNUROPHYCEAE IN A SMALL NEW ENGLAND LAKE: IMPLICATIONS FOR PALEOLIMNOLOGICAL RESEARCH1

The seasonal periodicity of taxa of Chrysophyceae and Synurophyceae from a small New England lake is described for the period September 1983 through June 1988. We found 51 taxa, including 29 that accounted for over 10% of the total in at least one collection. The taxa were fitted into one of five seasonal patterns. Patterns I and II represented taxa restricted to warm (pattern I) or cold (pattern II) months, respectively. Pattern HI represented organisms that began growth in the summer, persisted through autumn and disappeared with the onset of an ice cover. Pattern IV was an extension of pattern III, in which the taxon remained in the plankton throughout the winter and disappeared soon after ice out. Species without a clear seasonal pattern were grouped as pattern V. The seasonal periodicity of the flora, as examined with ordination analyses, was found to remain remarkedly similar during the 58–month study. Except for episodes of low pH during spring snow melt and unseasonally warm or cold weather, sample scores followed a fairly consistent pattern along the first and second primary axes. Water temperature, specific conductance, and pH were important variables that controlled changes in the species composition during the course of a given year. The flora was used to develop an inference model for water temperature. According to the analyses, the remains of a surface sediment sample represented a flora that grew primarily during the late autumn period at 7.6 ° C. Ways in which seasonal data could be utilized to improve paleolimnological inference work are discussed.     

ULTRASTRUCTURE OF PRYMNESIUM NEMAMETHECUM SP. NOV. (PRYMNESIOPHYCEAE)1

Based on material collected from Cape Town, a new sand-dwelling, marine species of Prymnesium is described. Using light and electron microscopy, Prymnesium nemamethecum sp. nov. has been found to resemble other species of the genus in size, organelle arrangement, and swimming behavior. It differs from other described species in that it has three types of scales, one of which is confined to the region of appendage insertion and forms a sheath of simple plate scales over the haptonema. In addition, the scales constituting the proximal body scale layer(s) are unusual because they are not simple plate scales but are specifically ornamented.     

ULTRASTRUCTURE OF CYST FORMATION IN OCHROMONAS TUBERCULATA (CHRYSOPHYCEAE)1

The cysts (statospores) of Ochromonas tuberculata Hibberd are produced within a cytoplasmic silica deposition vesicle (SDV) whose membrane (silicalemma) appears to be formed by the coalescence of golgi vesicles. Silica is first deposited as small nodules and the collar and spines develop by centrifugal growth only after a complete but still thin wall has been laid down. Small vesicles appear to be attached to the SDV only in the region overlying the developing collar; a cap of radially arranged, moderately electron-dense material occurs at the tip of the growing spines. The cyst pore is formed at the anterior end of the flagellate cell, by lack of silica deposition over a small region of the SDV and rupture of the SDV and other membranes crossing this region. When the cyst wall is complete, an extracystic plug is formed in the pore, resulting in the loss of some extracystic cytoplasm and the plasmalemma, and the inner SDV membrane becomes the functional plasmalemma. The plug develops first by coalescence with the cell membrane of golgi-derived vesicles containing dense but apparently nonsiliceous spicules surrounded by amorphous material. During later stages of plug formation only fibrous material is deposited, some of which may be extruded through the pore forcing out some of the spiculate component. Scanning electron micrographs of the mature wall show it is smooth except for the concentrically wrinkled inner face of the flared collar and that the real pore diameter is only ca. half that of the collar. At germination the plug completely disappears in an unknown way and a single cell, similar to a normal vegetative cell emerges through the pore. Chrysophycean cyst formation generally resembles cell wall formation in diatoms, but differs in some details.     

A PHYLOGENETIC ANALYSIS OF THE SYNUROPHYCEAE USING MOLECULAR DATA AND SCALE CASE MORPHOLOGY

The phylogeny of the Synurophyceae was investigated by parsimony analysis of scale case characters and small-sub unit (18S) ribosomal RNA (rRNA) sequence data. Analysis of 1 eustigmatophycean (outgroup), 3 chrysophycean, and 10 synurophycean 18S rRNA sequences corroborated the inference from ultrastructural information that the Synurophyceae is a monophyletic assemblage . Tessellaria vol-vocina, which had been tentatively proposed as a member of the Synurophyceae, was confirmed as the earliest lineage within the Synurophyceae by both the molecular analysis and an evaluation of published ultrastructural data. A second set of analyses investigated the relationships among Tessellaria volvocina, 6 Synura species, and 10 Mallomonas species/varieties, with particular reference to the validity of current classifications of the Synurophyceae and the characters upon which they are based. The molecular and scale case phylogenies were not totally resolved but were largely congruent. The data sets were combined to produce another phylogeny, which showed greater resolution. The combined phylogeny weakly supported our representatives of Synura and Mallomonas as monophyletic groupings and also upheld several of the sections within these genera that are recognized by current classifications. However, some changes to the classification and delineation of these genera are recommended and predicted. Both our 18S rRNA sequence and scale case data sets were more appropriate for examining the branching order among the more closely related text rather than resolving the deeper branching points of the synurophycean phylogeny .     

A NEW PHYLOGENY FOR CHROMOPHYTE ALGAE USING 16S-LIKE RRNA SEQUENCES FROM MALLOMONAS PAPILLOSA (SYNUROPHYCEAE) AND TRIBONEMA AEQUALE (XANTHOPHYCEAE)1

The 16S-like ribosomal RNA genes from Mallomonas papillosa Harris et Bradley (Synurophyceae) and Tribonema aequale Pascher (Xanthophyceae) were sequenced and compared to those of other eukaryotes. Mallomonas is closely related to Ochromonas (Chrysophyceae) and supports the general hypothesis of a close phylogenetic relationship between the Synurophyceae and Chrysophyceae. Tribonema is specifically related to Costaria costata (C. A. Agardh) Saunders (Phaeophyceae) demonstrating an unexpected phylogenetic relationship between the Xanthophyceae and Phaeophyceae. Distance and parsimony analysis place these four chromophyte genera in a complex evolutionary assemblage that includes the Bacillariophyceae and Oomycetes but excludes the Dinophyceae. The close relationship between the chromophyte algae and the Öomycete fungi supports the hypothesis that protists with tripartite hairs form a natural assemblage.     

SCALED CHRYSOPHYTES (CHRYSOPHYCEAE AND SYNUROPHYCEAE) FROM ADIRONDACK DRAINAGE LAKES AND THEIR RELATIONSHIP TO ENVIRONMENTAL VARIABLES1

The relationships between 23 scaled chrysophyte taxa (Chrysophyceae and Synurophyceae) and measured limnological variables in 62 Adirondack, New York, drainage lakes were examined by canonical correspondence analysis (CCA). The major proportion of variation in chrysophyte species distributions was strongly related to total monomeric Al (Al_m) and Mg concentrations, and their close correlates pH, Na, Ca, and acid-neutralizing capacity (ANC). Total monomeric Al concentrations explain a greater proportion of species variation than pH, suggesting that Al_m concentrations may be more important in governing the distribution of chrysophyte taxa in these lakes. Gaussian logit (GL) and linear logit (LL) regressions of the relative percentages of individual chrysophyte taxa to lakewater pH and Al_m concentrations and the examination of pH–Al_m response surfaces show that many chrysophyte taxa exhibit unique responses to these environmental gradients; taxa can be characterized as alkaline, circumneutral, acidic, and pH indifferent. Within each of these groups, taxa can be characterized further based upon their optima and tolerances to Al_m concentrations. Chrysophyte indicator species (i.e. a taxon with a strong statistical relationship to the environmental variable of interest, a well-defined optimum, and a narrow tolerance to the variable of interest) for pH include Mallomonas hindonii, M. crassisquama, M. pseudocoronata, and Synura uvella; M. hindonii, M. crassisquama, M. pseudocoronata, S. petersenii, and S. spinosa are good indicators of Al_m concentrations. Highly significant predictive models were developed to infer lakewater pH and Al_m concentrations from the relative percentages of chrysophyte scales in the study lakes. Model evaluation was based on their correlation coefficients and the root-mean-squared error of prediction (RMSE) derived from bootstrapping. Weighted averaging regression and calibration with tolerance down-weighting (i.e. weighting taxa inversely to their variance) produced superior results when compared to the computationally and data-demanding maximum likelihood methods and to simple weighted averaging regression and calibration.     

THE ULTRASTRUCTURE OF PYRAMIMONAS PSEUDOPARKEAE SP. NOV. (PRASINOPHYCEAE) FROM SOUTH AFRICA1

The ultrastructure of Pyramimonas pseudoparkeae sp. nov., a member of the class Prasinophyceae occurring in tidal pools along the east, south and west coast of South Africa, is described. The cell surface is covered by three distinctive body scales whilst the flagellar surfaces possess four types of scales. The structure of these scales is described. P. pseudoparkeae resembles Pyramimonas parkeae Norris and Pearson but differs in the structure of the type 2 body scale. The symmetry and ultrastructure of the cell are described with special attention given to the flagellar apparatus. Preliminary information on the life cycle of this species is presented. This new species is compared with other closely related members of the genus Pyramimonas.     

ULTRASTRUCTURE OF GLOEODINIUM MONTANUM (DINOPHYCEAE)1

The freshwater dinoflagellate Gloeodinium montanum Klebs (1912) was examined with transmission and scanning electron microscopy. Micrographs of ultrathin sections revealed a series of membrane layers rather than the usual dinoflagellate theca in vegetative cysts and in legates. Swarmers had distinct pellicles but appeared to be devoid of thecal plates and vesicles. The organization of cysts and swarmers appeared remarkably similar. All cell types had typical dinoflagellate nuclei with condensed chromosomes. Chloraplasts had girdle lamellae. One pyrenoid per cell was also present in chloroplasts of vegetative cysts. Starch grains and oil globules were distributed throughout the cytoplasm. Large accumulation bodies and polyvesicular vacuoles were found in aging cysts. Trichocysts and flagellar hairs were absent. Two types of intra-cellular prokaryotic organisms were discovered.     

Morphological evolution of silica scales in the freshwater genus Synura (Stramenopiles)

A high degree of morphological variability is expressed between the ornately sculptured siliceous scales formed by species in the chrysophycean genus, Synura. In this study, we aimed to uncover the general principles and trends underlying the evolution of scale morphology in this genus. We assessed the relationships among thirty extant Synura species using a robust molecular analysis that included six genes, coupled with morphological characterization of the species‐specific scales. The analysis was further enriched with addition of morphological information from fossil specimens and by including the unique modern species, Synura punctulosa. We inferred the phylogenetic position of the morphologically unique S. punctulosa, to be an ancient Synura lineage related to S. splendida in the section Curtispinae. Some morphological traits, including development of a keel or a labyrinth ribbing pattern on the scale, appeared once in evolution, whereas other structures, such as a hexagonal meshwork pattern, originated independently several times over geologic time. We further uncovered numerous construction principles governing scale morphology and evolution, as follows: (i) scale roundness and pore diameter decreased during evolution; (ii) elongated scales became strengthened by a higher number of struts or ribs; (iii) as a consequence of scale biogenesis, scales with spines possessed smaller basal holes than scales with a keel and; and (iv) the keel area was proportional to scale area, indicating its potential value in strengthening the scale against breakage.     

GROWTH RATES AND ULTRASTRUCTURE OF SILICEOUS SETAE OF CHAETOCEROS GRACILIS (BACILLARIOPHYCEAE) 12

The growth of setae in post-division Chaeloceros gracilis Schütt was triphasic. Following cell separation there was an initial lag phase of about 30 min after which setae grew linearly at rates ranging from 0.20 to 0.38 μm-min^?1. The growth rate was independent of whether diatoms cultured in medium containing 200 μM Si were transferred for experimentation to media containing 10 or 200 μM Si. When developing setae had attained a length of approximately 2 μm, their growth rate slowed as they entered a clearly defined plateau phase. The amount of silicon per unit length of setae was found to be 0.02 pg Si μm^?1, and the deposition rate was estimated as 0.005 Pg Si min^?1. Transmission electron microscopy revealed an axial structure resembling a microlubule extending the length of each seta and membrane bound polyphosphate bodies postulated to be the energy source for growth and associated biomineralization processes.     

PLASTID DIVISION IN MALLOMONAS (SYNUROPHYCEAE,HETEROKONTA)1

Laser scanning confocal microscopy and TEM were used to study the morphology of secondary plastids in algae of the genus Mallomonas (Synurophyceae). At interphase, Mallomonas splendens (G. S. West) Playfair, M. rasilis Dürrschm., M. striata Asmund, and M. adamas K. Harris et W. H. Bradley contained a single H‐shaped plastid consisting of two large lobes connected by a narrow isthmus. Labeling of DNA revealed a necklace‐like arrangement of plastid nucleoids at the periphery of the M. splendens plastid and a less‐patterned array in M. rasilis. The TEM of M. splendens and M. rasilis showed an electron‐dense belt surrounding the plastid isthmus in interphase cells; this putative plastid‐dividing ring (PD ring) was adpressed to the inner pair of the four plastid membranes, suggesting that it is homologous to the PD ring of green and red plastids. The PD ring did not contain actin (indicated by lack of staining with phalloidin) and displayed filaments or tubules of 5–10 nm in diameter that may be homologous to the tubules described in red algal PD rings. Confocal microscopy of chl autofluorescence from M. splendens showed that the plastid isthmus was severed as mitosis began, giving rise to two single‐lobed daughter plastids, which, as mitosis and cell division progressed, separated from one another and then each constricted to form the H‐shaped plastids of daughter cells. Similar plastid division cycles were observed in M. rasilis and M. adamas; however, the plastid isthmus of M. striata was retained throughout most of cell division and was eventually severed by the cell cleavage furrow.     

ULTRASTRUCTURE OF THE FLAGELLAR APPARATUS OF PYROBOTRYS (CHLOROPHYCEAE)1

The flagellar apparatus of Pyrobotrys has a number of features that are typical of the Chlorophyceae, but others that are unusual for this class. The two flagella are inserted at the apex, but they extend to the side of the cell toward the outside of the colony, here designated as the ventral side. Four basal bodies are present, two of which extend into flagella. Four microtubular rootlets alternate between the functional and accessory basal bodies. In each cell, the two ventral rootlets are nearly parallel, but the dorsal rootlets are more widely divergent. The rootlets alternate between two and four microtubules each. A striated distal fiber connects the two functional basal bodies in the plane of the flagella. Two additional, apparently nonstriated, fibers connect the basal bodies proximal to the distal fiber. Another striated fiber is associated with each four-membered rootlet near its insertion into the flagellar apparatus. A fine periodic component is associated with each two-membered rootlet. A rhizoplast-like structure extends into the cell from each of the functional basal bodies. The arrangement of these components does not reflect the 180° rotational symmetry that is usually present in the Chlorophyceae, but appears to be derived from a more symmetrical ancestor. It is suggested that the form of the flagellar apparatus is associated with the unusual colony structure of Pyrobotrys.     

Silica-scaled chrysophytes (Synurophyceae) from some rivers and shallow lakes in Hungary

Silica-scaled chrysophytes are a special group in the phytoplankton of rivers and shallow lakes. They are present the whole year at low density, but sometimes — mainly during autumn and spring — some species can become frequent and very numerous to form real water blooms.In this study, seven species of silica-scaled chrysophytes have been recorded and identified by electron microscopy of phytoplankton samples from some rivers and shallow lakes in Hungary. Most of these silica-scaled chrysophytes have previously been found in eutrophic and hypertrophic localities, and almost all of them are common and widely distributed, even cosmopolitan. Only Synura echinulata Korshikov has not previously been recorded from Hungary. Some of them as Synura curtispina (Petersen & Hansen) Asmund, S. petersenii Korshikov, Mallomonas acaroides Perty emend. Ivanov, M. tonsurata Teiling were frequently found in the phytoplankton samples. Sometimes in autumn and winter Synura petersenii was the most abundant species in the phytoplankton and formed blooms.     

THE ULTRASTRUCTURE OF MEIOSPORES OF COLEOCHAETE PULVINATA (CHAROPHYCEAE)1

In view of the relative importance of reproductive cell ultrastructure in phylogenetic and systematic studies of green algae, we investigated the fine structure of germinating zygotes and meiospores of Coleochaete pulvinata Braun. Meiospores have a flagellar apparatus very similar to that of zoospores and spermatozoids of the same species. Meiospores differ from zoospores and spermatozoids of C. pulvinata in having pyramidal body scales similar to those present on zoospores of C. scutata. Meiospores of C. pulvinata had as many as twice the number of spline microtubules as zoospores, and four times the number present in splines of spermatozoids of the same species. Developing meiospores of C.pulvinata, like those of other Coleochaete species, are individually surrounded by chamber walls. These differed from vegetative cell walls in lacking plasmodesmata. Moreover, the chamber walls in germinating zygotes of C.pulvinata stained a cobalt blue color with resorcinal blue, and fluoresced yellow in the presence of aniline blue, thus exhibiting the staining characteristics of callose. In location, morphology and presence of callose, chamberwalls resemble “special walls” of land plants, they may represent a charophycean spore development preadaptation useful in the evolution of walled spores characteristic of land     

ULTRASTRUCTURE OF MALE GAMETES OF SPHAEROPLEA ROBUSTA (CHLOROPHYCEAE)1

Male gametes have been studied in Sphaeroplea robusta (Chlorophyceae) using both light and electron microscopy. Mature gametes are typically biflagellate and possess a single, large mitochondrion that dominates the anterior third of the cell, directly posterior to the basal bodies. One or more microbodies are closely associated with the mitochondrion. Contractile vacuoles occur anterior to the elongated nucleus which, in fully mature gametes, possesses condensed chromatin. The reduced, starch-filled chloroplast lacks an associated eyespot and occupies a posterior position. A thin, anteriorly directed process or extension of the chloroplast parallels a portion of one of the multistranded flagellar roots. The paired basal bodies are directly opposed with no demonstrable offset, and are connected by an arched distal fiber with a highly elaborated central striated region that forms the apical cone, a feature characteristic of male gametes in most species of Sphaeroplea. Possession of a striated distal fiber, a cruciate flagellar root system (i.e. two-stranded microtubular roots alternating with multistranded roots), and directly opposed basal bodies are consistent with the alga's chlorophycean affinities.     

ULTRASTRUCTURE OF THE GAMETE OF PEDIASTRUM DUPLEX (CHLOROPHYCEAE)1

Gametes of Pediastrum duplex Meyen were investigated ultrastructurally, with emphasis on the flagellar apparatus. The cells are naked, biflagellate, and measure approximately 2.5 × 8 μm. Distinguishing them from zoospores is their possession of an eyespot and mating structure (the apical cap), and their lack of the peripheral band of cytoplasmic microtubules involved in colony formation. Four featurs of the flagellar apparatus are especially noteworthy: (1) the basal bodies are directly opposed and (2) are interconnected via their cores, (3) the central portion of the distal fiber is elaborated into an unusual ribbed structure which overlies the striated microtubule-associated component (SMAC) of the two-membered rootlets, and (4) the X-rootlets are dissimilar in microtubular number. The smaller X-rootlet consists of four microtubules in a three over one (3/1) configuration, whereas the larger has been found to be either 5 / 1, 6 / 1 or 7 / 1. The former rootlet extends past the nucleus whereas the latter extends down the opposite side of the cell, passing near the eyespot. The first two of these flagellar apparatus features have been previously noted in other motile cells of the Hydrodictyaceae. Although not specifically mentioned, published micrographs suggest the presence of the latter two as well, which may indicate that all four flagellar apparatus features are characteristics of all motile cells in the Hydrodictyaceae.     

ULTRASTRUCTURE OF TETRASPOROGENESIS IN PALMARIA PALMATA (RHODOPHYTA)1

The tetrasporangial initial in Palmaria palmata (L.) O. Kuntze (formerly Rhodymenia palmata (L.) Greville) arises from a cortex cell which enlarges and deposits a protein-rich wall layer. This cell undergoes mitosis to form a tetrasporocyte and a stalk cell. Synaptonemal complexes are formed in the sporocyte nucleus while in the cytoplasm floridean starch is deposited in association with ER or with particles presumed to be ribosomes. Microbody-like structures become numerous between the nuclear envelope and perinuclear ER, and clusters of non-membranous, spherical structures also are associated with the nucleus. Chromatin condensation is reversed following pachytene and a prolonged diffuse stage ensues, when dictyosomes and ER produce vesicles which deposit mucilage rich in sulfated and acidic polysaccharides around the tetrasporocyte. A conspicuous lenticular thickening of the mucilage sheath develops at the apical end of the sporangium. Dictyosomes are frequently associated with mitochondria which may be associated with chloroplasts. Following nuclear divisions the tetrasporocyte is cleaved into four spores by sequentially initiated, but simultaneously completed periclinal and anticlinal furrows. When mucilage deposition ceases, the dictyosomes begin to produce vesicles with glycoprotein-rich contents. These vesicles are abundant in released tetraspores, and they probably contain adhesive material aiding in the attachment of the liberated spores.