Ultrastructure of the early stages of carposporophyte development in the red algaChondria tenuissima (Rhodomelaceae,Ceramiales)

The ultrastructure of the early stages of carposporophyte development in the marine red algaChondria tenuissima has been studied. The diploid carposporophyte grows on the gametophyte. Apical gonimoblast cells develop into diploid carpospores. The basal gonimoblast cells cease to divide and undergo considerable cytoplasmic changes before they become incorporated into the expanding fusion cell. Nucleus and plastids degenerate gradually, while mitochondria remain intact. The smooth endoplasmic reticulum becomes prominent, it seems to produce small vesicles with electron dense contents. Simultaneously, numerous mucilage sacs are formed, presumably from dilating ER cisternae. The contents of the mucilage sacs are secreted by exocytosis. The pit connections between gonimoblast cells flare out. They remain as isolated bodies without connection to a wall after fusion. Secondary pit connections occur between vegetative gametophyte cells and sterile carposporophyte cells. There are three different morphological types of pit connections.     

Structure of pollen grains of Tradescantia reflexa with special reference to the generative cell and the ER around it

A pollen grain in Tradescantia reflexa consists of two cells, the generative and the vegetative cells, the generative cell being surrounded completely by the vegetative cell. The generative cell has many lobes or surface invaginations. A complicated network of rER extends throughout the entire vegetative cytoplasm, forming a system of channels made up by the cisternae of rER. Lipid granules are surrounded by ER. Branches of the rER enter all the concavities of the invaginations and attach to the plasma membranes at the bottoms of the invaginations. In the generative cell, no reserve substances, such as lipids, are seen. There is little ER, mitochondria are few in number, and Golgi bodies seem to be less active within this type of cell. Bundles of microtubules run parallel to the long axis of the generative cell. No microtubules or microfilaments can be detected at or near the bottoms of concavities, either on the generative or the vegetative side. ER is the sole cell element that bears a positional relationship to the invaginations. It appears, therefore, that rER is intimately involved in the shaping of the invaginations. This is the first report that a cell element other than microtubules and microfilaments can be involved in the formation of the outer shape of a cell. The possibility that materials from decomposed lipid droplets are transported through the rER to the generative cell is also discussed.     

A re-examination of the morphology and reproduction of Nothocladus lindaueri (Batrachospermales, Rhodophyta)

The vegetative morphology and reproduction of the freshwater rhodophyte Nothocladus lindaueri Skuja [=Batrachospermum lindaueri (Skuja) Necchi et Entwisle] were examined by light and electron microscopy. It was confirmed that this alga has a typical batrachospermalean pit plug with two cap layers, the outer one of which is domed. During elongation of hair cells, the primary wall is broken, forming a basal collar. Hair cells have a single nucleus and abundant Golgi bodies, en-doplasmic reticula (ER) and vesicles. Dividing apical cells of the fascicles have a nucleus with art adjacent zone of exclusion, the latter containing a single polar ring. Branched trichogynes and fertilized carpogonia are shown for the first time in this species. Carpogonial branch and involucral cells contain a prominent axial nucleus, proplastids, ER and vesicles. The pit plugs disintegrate among these cells leaving open pit connections. Carpogonia have plentiful mitochondria and vesicles. The wall at the trichogyne apex is thickened and densely stained. The carposporophyte centre consists of a mass of fusion cells with open pit connections, and indeterminate gonimoblast filaments arise from this mass. The combination of a symmetrical carpogonial base, a carposporophyte centre consisting of a mass of fusion cells, and exclusively indeterminate gonimoblast filaments appears to be unique among the members of the Batrachospermaceae. The specimen of N. lindaueri contains epiphytic filaments of Audouinella meiospora producing both spermatangia and monosporangia. Spermatium formation in N. lindaueri remains unknown.     

DEVELOPMENT OF THE FLAGELLAR APPARATUS AND FLAGELLAR ORIENTATION IN THE COLONIAL GREEN ALGA GONIUM PECTORALE (VOLVOCALES)1

Vegetative cells of Gonium pectorale have a fine structure similar to that of Chlamydomonas. In addition, three zones comprise an extracellular matrix; a fibrillar sheath and tripartite boundary surround individual cells, and a fragile capsule zone surrounds the entire colony. Cytokinesis is accomplished by a phycoplast and cleavage furrow. The flagellar apparatus of the immature vegetative cell of this colonial alga is similar to that of Chlamydomonas, but the basal bodies are slightly separated at their proximal ends. The four microtubular rootlets alternate between two and four members. During development, the basal bodies become further separated and nearly parallel. The distal fiber is stretched, but it remains attached to both basal bodies. At maturity, the basal bodies of peripheral cells of the colony have rotated in opposite directions on their longitudinal axes resulting in a displacement of the distal fiber to one side, an asymmetrical orientation of the rootlets and loss of 180° rotational symmetry. Central cells remain similar to Chlamydomonas in that basal bodies do not rotate, rootlets are cruciate, the distal fiber remains medially inserted and 180° rotational symmetry is conserved. A “pin-wheel” configuration of flagellar pairs and the orientation of parallel rootlets toward the colony perimeter probably accounts for the rotation of the colonies during forward swimming. In addition, these ultrastructural features support the traditional placement of G. pectorale as an intermediate between the unicellular Chlamydomonas and the more complex colonial volvocalean genera.     

Ultrastructural studies of Austramphilina elongata (Cestoda,Amphilinidea)

Summary The fine structure of larval Austramphilina elongata is described using serial semithin and ultrathin sections. Densely packed germ cells with many ribosomes and mitochondria and with large Golgi complexes fill the middle third of the body. Some necrotic nuclei were observed near the anterior end. The neodermis consists of a subepidermal syncytium connected to pericarya in the parenchyma by means of cytoplasmic processes containing peripheral microtubules; electron-dense ovoid bodies condense in these processes. Myoblasts are connected to muscle fibres by means of cytoplasmic connections rich in mitochondria. Twelve (exceptionally eleven) type I gland cells containing large secretory granules and extensive granular endoplasmic reticulum are located in the dorso-posterior part of the body; they open through 12 (or 11) discrete ducts into an anterior invagination of the tegument which is covered by epidermis and not connected to the outside. Ten type II gland cells containing elongate secretory granules with regularly arranged longitudinal microtubules are located ventral to the type I cell bodies; they open on a ventral papilla a short distance behind the anterior end. Ten type III gland cells containing irregularly round-oval secretory granules with coiled microtubules are located anterior and ventral to the type I gland cells; they open through five discrete ventro-anterior openings on each side of the body. Ducts of all gland cells have mitochondria and microtubules. The spermatozoon has a basic pattern of two axonemes, each with a single central filament, a mitochondrion (mitochondria), and a row of surface microtubules interrupted by the axonemes. In the tips of epidermal cilia, doublet 1 and doublets adjacent to it lose their microtubules B first and close in on the central pair of filaments in a spiral fashion, enclosing an electron-dense rod. Presence of a neodermis and ultrastructure of the spermatozoon support the validity of the taxa Neodermata Ehlers and Trepaxonemata Ehlers and are strong evidence against a phylogenetic relationship of the cestodarians — cestodes with the Acoelomorpha; this is also indicated by the ultrastructure of sense receptors and epidermal ciliary rootlets.     

An ultrastructural investigation of the hypocerebral organ of the adult Euperipatoides kanangrensis (Onychophora, Peripatopsidae)

The hypocerebral organs of Euperipatoides kanangrensis are a pair of spherical vesicles located ventral to the cerebral ganglia. They develop in the embryo from the most anterior pair of ventral organs, in the antennal segment. The wall of each hypocerebral organ is a dense epithelium of elongate cells with peripheral nuclei. The cytoplasm of the cells includes numerous mitochondria, Golgi bodies and microtubules. The small lumen, located eccentrically within the organ, contains concentrically layered electron-dense material resembling cuticle.Each hypocerebral organ is enclosed by a layer of extracellular matrix continuous with that surrounding the adjacent cerebral ganglion. There are no nerve connections between ganglion and organ, but cellular connections traverse the intervening matrix and could serve as a communication pathway. The ultrastructure of the hypocerebral organs indicates that they are glands.     

Discovery of a resting stage in the harmful,brown‐tide‐causing pelagophyte,Aureoumbra lagunensis: a mechanism potentially facilitating recurrent blooms and geographic expansion

To date, the life stages of pelagophytes have been poorly described. This study describes the ability of Aureoumbra lagunensis to enter a resting stage in response to environmental stressors including high temperature, nutrient depletion, and darkness as well as their ability to revert from resting cells back to vegetative cells after exposure to optimal light, temperature, and nutrient conditions. Resting cells became round in shape and larger in size, filled with red accumulation bodies, had smaller and fewer plastids, more vacuolar space, contained lower concentrations of chl a and RNA, displayed reduced photosynthetic efficiency, and lower respiration rates relative to vegetative cells. Analysis of vegetative and resting cells using Raman microspectrometry indicated resting cells were enriched in sterols within red accumulation bodies and were depleted in pigments relative to vegetative cells. Upon reverting to vegetative cells, cells increased their chl a content, photosynthetic efficiency, respiration rate, and growth rate and lost accumulation bodies as they became smaller. The time required for resting cells to resume vegetative growth was proportional to both the duration and temperature of dark storage, possibly due to higher metabolic demands on stored energy (sterols) reserves during longer period of storage and/or storage at higher temperature (20°C vs. 10°C). Resting cells kept in the dark at 10°C for 7 months readily reverted back to vegetative cells when transferred to optimal conditions. Thus, the ability of Aureoumbra to form a resting stage likely enables them to form annual blooms within subtropic ecosystems, resist temperature extremes, and may facilitate geographic expansion via anthropogenic transport.     

Ultrastructure of the Somatic Cortex of the Gymnostome Ciliate Spathidium spathula (O. F. M.)1

The somatic cortex of Spathidium spathula is described ultrastructurally. The pellicle consists of an outer membrane and an underlying alveolar system. Numerous membrane-bound mucocysts and spherical electron-opaque bodies have similar circular sites of attachment to the outer membrane. Below these are a microfibrillar zone and an underlying region of rough ER. Mitochondria are lined up under the rough ER in longitudinal cortical ridges. Parasomal sacs are found near the basal bodies and are associated with cytoplasmic membranous sacs. Various microtubular and fiber systems are associated with single basal bodies: (1) a short kinetodesmal fiber; (2) two transverse microtubular ribbons and a transverse fiber; (3) a postciliary microtubular ribbon, initially sandwiched by two fibers, which gives rise to longitudinal subpellicular microtubules extending posteriorly for a distance of some four or five basal bodies; and (4) a system of overlapping subkinetal microtubules. A three-dimensional reconstruction is included. The somatic cortex of S spathula is similar to that reported for other Haptorida of the ciliate subclass Gymnostomata.     

ULTRASTRUCTURE OF VEGETATIVE AND DIVIDING CELLS OF THE UNICELLULAR RED ALGAE RHODELLA VIOLACEA AND RHODELLA MACULATA1

Rhodella violacea (Kornmann) Wehrmeyer and Rhodella maculata Evans were investigated for ultrastructural details of vegetative and dividing cells. Rhodella violacea has a nuclear projection into the pyrenoid similar to that found in R. maculata, although the nuclear projection in R. maculata traverses a starch-lined area before contacting the pyrenoid. Unlike most, red algae, the two Rhodella species lack a peripheral encircling thylakoid in the chloroplast and have dictyosomes associated solely with endoplasmic reticulum (ER) instead of with both mitochondria and ER. Both species also have a well-developed peripheral system of ER connected to the plasmalemma by tubules, a situation found only in red algal unicells, Cell division was studied primarily in R. violacea; a less thorough examination of R. maculata showed no essential differences. Both have small, double-ringed, nucleus-associated organ files (NAOs) surrounded by moderately electron-dense material, metaphase–anaphase polar gaps in the nuclear envelope, absence of perinuclear ER. and short interzonal spindles. This pattern of mitosis is similar in most respects to that reported in the unicell Flintiella. Following mitosis, microtubules extend from the region of each NAO to its associated nucleus and to the undivided pyrenoid. The NAOs appear to apply tension to the nuclei and the pyrenoid and may be the mechanism for ensuring equal partitioning of both organdies. Two different forms of pyrenoid-nucleus association occur during mitosis. Nuclear projections into the pyrenoid, prevalent during interphase and early stages of mitosis, recede at metaphase. Then, the pyrenoid extends protrusions into the nuclear polar areas, forming a cup that partially surrounds the nucleus. Cell division and vegetative characters confirm the close taxonomic affinity of these two species of Rhodella and support their separation from the genus Porphyridium.     

THE FINE STRUCTURE OF MITOSIS AND CELL DIVISION IN THE CHRYSOPHYCEAN ALGA OCHROMONAS DANICA1

At the ultrastructural level, cell division in Ochromonas danica exhibits several unusual features. During interphase, the basal bodies of the 2 flagella replicate and the chloroplast divides by constriction between its 2 lobes. The rhizoplast, which is a fibrous striated root attached to the basal body of the long flagellum, extends under the Golgi body to the surface of the nucleus in interphase cells. During proprophase, the Golgi body replicates, apparently by division, and a daughter rhizoplast, appears. During prophase, the 2 pairs of flagellar basal bodies, each with their accompanying rhizoplast and Golgi body, begin to separate. Three or 4 flagella are already present at this stage. At the same time, there is a proliferation of microtubules outside the nuclear envelope. Gaps then appear in the nuclear envelope, admitting the microtubules into the nucleus, where they form a spindle. A unique feature of mitosis in O. danica is that the 2 rhizoplasts form the poles of the spindle, spindle microtubules inserting directly onto the rhizoplasts. Some of the spindle microtubules extend from pole to pole; others appear to attach to the chromosomes. Kinetochores, however, are not present. The nuclear envelope breaks down, except, in the regions adjacent, to the chloroplasts; chloroplast ER remains intact throughout mitosis. At late anaphase the chromosomes come to lie against part of the chloroplast ER. This segment of the chloroplast ER appears to be incorporated as part of the reforming nuclear envelope, thus reestablishing the characteristic nuclear envelope—chloroplast ER association of the interphase cell.     

ONTOGENY,HISTOCHEMISTRY AND FINE STRUCTURE OF CELLULAR INCLUSIONS IN VEGETATIVE CELLS OF ANTITHAMNION DEFECTUM (CERAMIACEAE,RHODOPHYTA)1

The ultrastructure and histochemistry of developing and mature cell inclusions in vegetative cells of Antithamnion defectum Kylin were examined. Those studied were chloroplast inclusions, cytoplasmic crystals and spherical bodies within the vacuole. Chloroplasts of mature vegetative cells contain an interthylakoidal, apparently noncrystalline deposit of undetermined chemical identity. The bodies are parallel to the long axis of the plastid, are square (0.13 μm) in cross-section, and up to 3 μm long. Spherical vacuolar bodies (0.5–1.5 μum diam) are formed during early stages of vacuole formation by accumulation of protein deposits in swelling endoplasmic reticulum (ER) cisternae. Swelling of smooth ER contiguous to the ER containing the deposits results in the vacuole enclosing the spherical bodies. In mature cells, vesicles appear to be secreted into the preformed vacuole. Cytoplasmic proteinaceous crystalloids develop without a bounding membrane and may serve as protein reserves.     

Electron microscopic studies of the compound eye of the toadbug,Gelastocoris oculatus

There are eight retinula cells in the ommatidium of the compound eye of the toadbug (Gelastocoris oculatus), two of which are central in position. Along the axial sides of the six peripheral retinula cells expand six cytoplasmic processes from the apical crystalline cone cells. These processes, which contain longitudinally-oriented microtubules, are associated with all eight retinula cells by means of desmosomal junctions. In addition to providing structural support, the possibility is set forth that the interconnecting cone processes might also serve to functionally integrate the retinula cells of an ommatidium. The eight retinula cells possess microvillus surfaces, which are especially prominent in the six peripheral cells, where they extend into the lumen of the ommatidium. There is evidence of pinocytotic activity at the bases of microvilli. Multivesicular bodies are present in the cytoplasm of retinula cells, and the means by which these bodies might be elaborated are discussed.     

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.     

Cotton embryogenesis: The pollen tube in the stigma and style

Summary The ultrastructure and composition of the pollen tube of cotton (Gossypium hirsutum) growing in the tissues of the stigma and style of the flower were examined. The distal portion of the tube is densely cytoplasmic and contains the vegetative nucleus and the two sperms. The vegetative nucleus is highly convoluted and the membrane contains many pores and connections with the ER. No organized nucleolus is present but 4–6 membrane-bound, protein containing bodies are found in the nucleus. Mitochondria containing numerous cristae are abundant in the cytoplasm. Dictyosomes are also plentiful and are engaged in the production of many large vesicles. Rough ER is conspicuous and polysomes are found in the cytoplasm. Plastids are few in number, poorly developed, and contain little starch. Many uniform, small vesicles are found throughout the cytoplasm. Lipid bodies frequently with small vesicles associated with them are found in the tube. In the proximal region vacuoles form and the cytoplasm becomes pressed against the wall. In the transition zone the ER frequently becomes distended and filled with protein. The wall has two distinct layers: one strongly PAS positive, the other faintly PAS positive. The inner wall is apparently formed by the deposition of large dictyosome vesicles. Plug structure and development were studied.     

Dynein supports motility of endoplasmic reticulum in the fungus Ustilago maydis

The endoplasmic reticulum (ER) of most vertebrate cells is spread out by kinesin-dependent transport along microtubules, whereas studies in Saccharomyces cerevisiae indicated that motility of fungal ER is an actin-based process. However, microtubules are of minor importance for organelle transport in yeast, but they are crucial for intracellular transport within numerous other fungi. Herein, we set out to elucidate the role of the tubulin cytoskeleton in ER organization and dynamics in the fungal pathogen Ustilago maydis. An ER-resident green fluorescent protein (GFP)-fusion protein localized to a peripheral network and the nuclear envelope. Tubules and patches within the network exhibited rapid dynein-driven motion along microtubules, whereas conventional kinesin did not participate in ER motility. Cortical ER organization was independent of microtubules or F-actin, but reformation of the network after experimental disruption was mediated by microtubules and dynein. In addition, a polar gradient of motile ER-GFP stained dots was detected that accumulated around the apical Golgi apparatus. Both the gradient and the Golgi apparatus were sensitive to brefeldin A or benomyl treatment, suggesting that the gradient represents microtubule-dependent vesicle trafficking between ER and Golgi. Our results demonstrate a role of cytoplasmic dynein and microtubules in motility, but not peripheral localization of the ER in U. maydis.     

Microtubules in some unicellular glands of two leeches

Summary What appear to be two types of unicellular glands are found in the integument of the leech, Helobdella stagnalis. Type I cells are characterized by a peripheral, subplasmalemmal sack of rough endoplasmic reticulum and accumulations of secretory product in the form of small membrane bound droplets. Type II cells are characterized by large numbers of closely opposed sacks of rough endoplasmic reticulum and secretory product in the form of large, evidently amorphous accumulations of secretory product.Both cell types attenuate into long, slender processes through which the secretory product passes to the surface of the leech. Each process is characterized by a subplasmalemmal sack of ER which runs the entire length of the process and is continuous, at the proximal end of the process, with sacks of rough ER. Associated with the inner member of the ER membrane pair are microtubules with a diameter of approximately 240 Å.A similar arrangement of a subplasmalemmal ER sack associated with microtubules also is found in secretory processes of the leech, Macrobdella decora.The possible source and functions of these microtubules are discussed.This investigation was supported by Public Health Service grant number GM 723-04 of the National Institutes of Health.The author is greatly indebted to Dr. David B. Slautterback for his advice and encouragement during the course of this investigation.     

Lipid body biogenesis and the role of microtubules in lipid synthesis in Ornithogalum umbellatum lipotubuloids

Lipid bodies present in lipotubuloids of Ornithogalum umbellatum ovary epidermis take the form of a lens between leaflets of ER (endoplasmic reticulum) membrane filled with a highly osmiophilic substance. The two enzymes, DGAT1 [DAG (diacylglycerol) acyltransferase 1] and DGAT2 (DAG acyltransferase 2), involved in this process are synthesized on rough ER and localized in the ER near a monolayer surrounding entities like lipid bodies. After reaching the appropriate size, newly formed lipid bodies transform into mature spherical lipid bodies filled with less osmiophilic content. They appear to be surrounded by a half-unit membrane, with numerous microtubules running adjacently in different directions. The ER, no longer continuous with lipid bodies, makes contact with them through microtubules. At this stage, lipid synthesis takes place at the periphery of lipid bodies. This presumption, and a hypothesis that microtubules are involved in lipid synthesis delivering necessary components to lipid bodies, is based on strong arguments: (i) silver grains first appear over microtubules after a short [3H]palmitic acid incubation and before they are observed over lipid bodies; (ii) blockade of [3H]palmitic acid incorporation into lipotubuloids by propyzamide, an inhibitor of microtubule function; and (iii) the presence of gold grains above the microtubules after DGAT1 and DGAT2 reactions, as also near microtubules after an immunogold method that identifies phospholipase D1.     

Fine Structure of Gametogony and Oocyst Formation in Sarcocystis sp. in Cell Culture

Fine structure of gametocytes and oocyst formation of Sarcocystis sp. from Quiscalus quiscula Linnaeus grown in cultured embryonic bovine kidney cells was studied. Microgametocytes measured up to ～5 μm diameter. During nuclear division of the microgametocyte, dense plaques were found adjacent to the nucleus just beneath the pellicle; occasionally microtubules were present within these plaques. These microtubules subsequently formed 2 basal bodies with a bundle of 4 microtubules between them. Microgametocytes also contained numerous mitochondria, micropores, granules, vacuoles, and free ribosomes. Each microgamete was covered by a single membrane and consisted of 2 basal bodies, 2 flagella, a bundle of 4 microtubules, a perforatorium, a mitochondrion, and a long dense nucleus which extended anteriorly and posteriorly beyond the mitochondrion. The bundle of 4 microtubules is thought to be the rudiment of a 3rd flagellum. Macrogametes were covered by a double membrane pellicle, and contained a large nucleus (～2.5 μm), vacuoles, and a dilated nuclear envelope connected with the rough endoplasmic reticulum (ER). In young macrogametes (～4 μm), the ER was arranged in concentric rows in the cortical region, and several sizes of dense granules were found in the cytoplasm. However, in later stages (～8 μm) the ER was irregularly arranged and was dilated with numerous cisternae; only large dark granules remained and a few scattered polysaccharide granules were found. No Golgi apparatus or micropores were observed. After the disappearance of dark granules 5 concentric membranes appeared. Four of these fused to form an oocyst wall composed of a dense outer layer (～66 nm thick) and a thin inner layer (～7 nm). The 5th or innermost membrane surrounded the cytoplasmic mass which was covered by a 2-layered pellicle and contained a nucleus, small amounts of ER, large vacuoles, and mitochondria. The sexual stages described greatly resemble those of Eimeria and Toxoplasma.     

The flagellar apparatus of the golden algaSynura uvella: Four absolute orientations

Summary Flagellated vegetative cells of the colonial golden algaSynura uvella Ehr, were examined using serial sections. The two flagella are nearly parallel as they emerge from a flagellar pit near the apex of the cell. The photoreceptor is restricted to swellings on the flagella in the region where they pass through the apical pore in the scale case and the swellings are not associated with the cell membrane or an eyespot. A unique ring-like structure surrounds the axonemes of both flagella at a level just above the transitional helix. The basal bodies are interconnected by three striated, fibrous bands. Four short (<100 nm) microtubules lie between the basal bodies at their proximal ends. Two rhizoplasts extend down from the basal bodies and separate into numerous fine striated bands which lie over the nucleus. Three- and four-membered microtubular roots arise from the rhizoplasts and extend apically together. As the roots reach the cell anterior, the three-membered root bends and curves clockwise to form a large loop around the flagella; the four-membered root bends anticlockwise and terminates under the distal end of the three-membered root as it completes the loop. There are four absolute orientations, termed Types 1–4, in which the flagellar apparatus can occur. With each orientation type the positions of the Golgi body, nucleus, rhizoplasts, chloroplasts and microtubular roots change with respect to the flagella, basal bodies and photoreceptor. Two new basal bodies appear in pre-division cells, and three short microtubules appear in a dense substance adjacent to each new basal body. Based upon the positions of new pre-division basal bodies, a hypothesis is proposed to explain why there are four orientations and how they are maintained through successive cell divisions.     

A microtubular crystal associated with the Golgi field of Pleurochrysis scherffelii

Summary In young vegetative cells of the Chrysophycean alga Pleurochrysis scherffelii, a characteristic array of microtubules is associated with the Golgi apparatus. This novel structure is described from frozen-etched preparations. The microtubular crystals flank the Golgi stack at either side at an oblique angle and lie in between the Golgi and the periplastidal ER and a parietal vacuole. The microtubules have an outer diameter of 195–230 Å and are spaced in a hexagonal pattern with center-to-center distances of 300–330 Å. The crystals lie free in the cytoplasm and are not surrounded by a membrane although they frequently associate with membraneous elements of the parietal vacuole or periplastidal ER. The microtubules are interconnected by bridge-like links. Possible functions of these crystals, especially in relation to secretion and protoplast rotation, are discussed.The authors thank Drs. H. Falk (University of Freiburg) and D. J. Morré (Purdue University) for valuable discussions and Miss Marianne Winter for skillful technical assistance. This work was supported in part by N.S.F. grant GB-23047 to R.M.B., and the Deutsche Forschungsgemeinschaft, to W.W.F.Scale Formation in Chrysophycean Algae. II.