ULTRASTRUCTURE OF CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE): AUXOSPORE,RESTING SPORE AND VEGETATIVE CELL MORPHOLOGY1

The structure of the frustule of auxospores, resting spores and vegetative cells of Chaetoceros muelleri Lemm. are described with LM and SEM. Vegetative frustules are relatively small and lightly silicified, are not united into filaments, and appear unornamented under LM and SEM. The setae are circular to subcircular in transverse section with spines and puncta arranged in a spiral pattern. The resting spore and auxospore frustules are more silicified than the vegetative frustules and appear unornamented under LM and SEM. The auxospores of C. muelleri were previously unknown.     

OBSERVATIONS ON THE SURVIVAL AND GERMINATION OF RESTING SPORES OF THREE CHAETOCEROS (BACILLARIOPHYCEAE) SPECIES1,2

Resting spores (hypnospores) of Chaetoceros diadema (Ehrenberg) Gran, Chaetoceros vanheurckii Gran, and Chaetoceros didymus Ehrenberg were collected from a large plastic enclosure moored in Saanich Inlet, B.C., Canada. The effects of combinations of temperature and irradiance on the germination of these resting spores were investigated. Nutrient uptake, carbon fixation, and changes in the photosynthetic capacity of the germinating spores were also examined. Resting spores germinated optimally at combinations of temperature and irradiance similar to those in the environment during sporulation. They did not germinate at irradiances 1.3 μEin m^?2 s^?1 or temperatures >25.3° C. Nitrate, phosphate and silicate were taken up after the resting spores had germinated and resumed vegetative growth. Chlorophyll a fluorescence in vivo, and the DCMU-induced increase in in vivo fluorescence also increased after the resting spores had germinated. Resting spores began to fix carbon as soon as they were placed in light. Spores remained viable for at least 645 d. The length of time between first exposure to light and germination did not change during this period; however, the percentage of viable resting spores decreased markedly. None of the Chaetoceros spores germinated after 737 d of storage at 2–4° C in darkness.     

IMPACT OF IRON LIMITATION ON THE PHOTOSYNTHETIC APPARATUS OF THE DIATOM CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE)

Iron starvation induced marked increases in flavodoxin abundance and decreases in light-saturated and light-limited photosynthesis rates in the diatom Chaetoceros muelleri. Consistent with the substitution of flavodoxin for ferredoxin as an early response to iron starvation, increases of flavodoxin abundance were observed before declines of cell division rate or chl a specific photosynthesis rates. Changes in the abundance of flavodoxin after the addition of iron to iron-starved cells indicated that flavodoxin was not actively degraded under iron-replete conditions. Greater declines in light-saturated oxygen evolution rates than dark oxygen consumption rates indicated that the mitochondrial electron transfer chain was not affected as greatly by iron starvation as the photosynthetic electron transfer chain. The carbon:nitrogen ratio was unaffected by iron starvation, suggesting that photosynthetic electron transfer was a primary target of iron starvation and that reductions in nitrate assimilation were due to energy limitation (the C:N ratio would be expected to rise under nitrogen-limited but energy-replete conditions). Parallel changes were observed in the maximum light-saturated photosynthesis rate and the light-limited initial slope of the photosynthesis-light curve during iron starvation and recovery. The lowest photosynthesis rates were observed in iron-starved cells and the highest values in iron-replete cells. The light saturation parameter, I_k, was not affected by iron starvation, nor was the chl-to-C ratio markedly reduced. These observations were consistent with iron starvation having a similar or greater effect on photochemical charge separation in PSII than on downstream electron transfer steps. Declines of the ratio of variable to maximum fluorescence in iron-starved cells were consistent with PSII being a primary target of iron starvation. The functional cross-section of PSII was affected only marginally (<20%) by iron starvation, with the largest values observed in iron-starved cells. The rate constant for electron transfer calculated from fast repetition rate fluorescence was found to covary with the light-saturated photosynthesis rate; it was lowest in the most severely starved cells.     

PHYSIOLOGICAL VARIABILITY WITHIN TEN STRAINS OF CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE)1

The effects of temperature, ionic composition, and conductivity on growth rates of ten strains of Chaetoceros muelleri Lemmerman (mostly var. subsalsum Johan. & Rushf.) were studied. Lipid content of stressed and unstressed cells and fatty acid composition were also determined. Considerable physiological variability was observed in the ten strains, although principal components analysis of physiological data indicated that all strains fell into one of two major groups: C. muelleri (var. muelleri and var. subsalsum) and an undescribed Chaetoceros species morphologically close to C. muelleri var. subsalsum. A high degree of agreement was found among morphological, physiological, and biochemical data sets, indicating that physiological and biochemical data may be helpful in making taxonomic decisions in diatoms, particularly in taxa with few morphological characters. We also conclude that nonmorphological characters such as those employed in the present study can be used to test phylogenetic hypotheses formulated from traditional morphological data.     

SHORT-TERM RESPONSE OF THE DIADINOXANTHIN CYCLE AND FLUORESCENCE YIELD TO HIGH IRRADIANCE IN CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE)1

The relationship between the diadinoxanthin cycle and changes in fluorescence yield in the diatom Chaetoceros muelleri Lemm. (clone CH10, Amorient Aquafarm, Inc., Hawaii) was investigated. High-light-induced changes in fluorescence yield and xanthophyll de-epoxidation occurred very rapidly (first order rate constant 1.60 min^?1). The observed light-induced changes in diatoxanthin and diadinoxanthin concentration were consistent with a two-pool scheme for diadinoxanthin, one of which does not undergo de-epoxidation. Changes in xanthophyll concentration correlated with changes in in vivo absorbance indicating that diadinoxanthin cycle activity in vivo can be monitored spectrophotometrically. However, changes in cell absorbance were small relative to total optical absorption cross section. Increases in the concentration of diatoxanthin were linearly correlated with increases in the rate constant for thermal de-excitation in the antenna of photosystem II (PSII). Antenna quenching produced or mediated by diatoxanthin may, thus, protect the PSII reaction center in diatoms. Changes in the maximum fluorescence yield suggested that changes in the reaction center also contributed to nonphotochemical quenching of fluorescence. Thus, reaction center quenching affected the relationship between antenna quenching and changes in photochemical efficiency producing the effect of a decrease in fluorescence yield without a decrease in photochemical efficiency.     

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.     

OBSERVATIONS ON CHAETOCEROS BUCEROS (BACILLARIOPHYCEAE), A RARE TROPICAL PLANKTONIC SPECIES COLLECTED FROM THE MEXICAN PACIFIC1

Examination of net plankton samples from the Gulf of Tehuantepec (Mexican Pacific) yielded a rare tropical species of the genus Chaetoceros, C. buceros Karsten. This species is conspicuous because of its relatively large size, type of chain formation, and shape of the terminal setae. Electron microscopic study revealed other interesting characteristics: the intercalary values are more lightly silicified than the terminal valves and show a pattern of costae radiating form the center with various annuli (“central hyaline fields”) in the center of the valve face; both kind of valves are perforated by small poroids. Terminal valves possess several (21–30) slitlike and randomly oriented rimoportulae. Important morphological differences exist between the intercalary and the terminal setae. Morphological characters, comparision with related species, and the systematic position are discussed. A new section of the subgenus Hyalochaete, Conspicua, is proposed to include C. buceros.     

THE ULTRASTRUCTURE AND CYTOCHEMISTRY OF RESTING CELL FORMATION IN AMPHORA COFFAEFORMIS (BACILLARIOPHYCEAE)1

The ultrastructure of logarithmic-growing cells and of resting cells in laboratory cultures of Amphora coffaeformis (Ag.) Kütz. isolated from deep ocean water was examined using electron and light microscopy. The acid Phosphatase activity, chlorophyll a and lipid content were assessed at weekly intervals of resting cell formation during cold-dark treatment, simulating deep ocean water. Approximately 4 wk are required to complete resting cell formation. During the first week, the cytoplasm undergoes extensive transformation and lysosomal activity is observed. Large vacules decrease in size and many small ones develop, the mitochondria become fewer and one or more massive mitochondria appear possibly by fusion of smaller ones; the cytoplasm becomes densely granular. During the second and third week, the cytoplasm continues to contract, lipid bodies begin to develop and the plastid becomes densely stained. At the fourth week, the mature resting cell is formed containing one or more massive mitochondria, a well-formed plastid, and granular cytoplasm containing occasional lipid droplets. There is no change in frustule morphology and the cytoplasm does not produce a protective layer. The variation in chemical constituents correlates with microscopic structure of the cells. The fine structure of cells during growth resumption when exposed to light at 25 c is presented. Previous reports of viable, chlorophyll-containing cells at great depths in the ocean may be explained by the results reported in this paper.     

ULTRASTRUCTURAL CHARACTERIZATION OF THE LYTIC CYCLE OF AN INTRANUCLEAR VIRUS INFECTING THE DIATOM CHAETOCEROS CF. WIGHAMII(BACILLARIOPHYCEAE) FROM CHESAPEAKE BAY,USA1

Numerous microalgal species are infected by viruses that have the potential to control phytoplankton dynamics by reducing host populations, preventing bloom formation, or causing the collapse of blooms. Here we describe a virus infecting the diatom Chaetoceros cf. wighamii Brightw. from the Chesapeake Bay. To characterize the morphology and lytic cycle of this virus, we conducted a time‐course experiment, sampling every 4 h over 72 h following viral inoculation. In vivo fluorescence began to decline 16 h after inoculation and was reduced to <19% of control cultures by the end of experiment. TEM confirmed infection within the first 8 h of inoculation, as indicated by the presence of virus‐like particles (VLP) in the nuclei. VLP were present in two different arrangements: rod‐like structures that appeared in cross‐section as paracrystalline arrays of hexagonal‐shaped profiles measuring 12 ± 2 nm in diameter and uniformly electron‐dense hexagonal‐shaped particles measuring ～ 22–28 nm in diameter. Nuclei containing paracrystalline arrays were most prevalent early in the infection cycle, while cells containing VLP increased and then declined toward the end of the cycle. The proportion of nuclei containing both paracrystalline arrays and VLP remained relatively constant. This pattern suggests that rod‐like paracrystalline arrays fragmented to produce icosahedral VLP. C. cf. wighamii nuclear inclusion virus (CwNIV) is characterized by a high burst size (averaged 26,400 viruses per infected cell) and fast generation time that could have ecological implications on C. cf. wighamii population control.     

SPORE FORMATION IN THE LIFE CYCLES OF THE DIATOMS CHAETOCEROS DIADEMA AND LEPTOCYLINDRUS DANICUS1

A nitrogen limitation technique elicited the entire life cycle of the marine centric diatoms Chaetoceros diadema (Ehr.) Gran and Leptocylindrus danicus Cleve. In C. diadema the sexual cycle followed the same pattern as in the previously investigated C. didymus. Sexuality took place in narrow diameter cells, only at 2 and 5° C, and was seldom seen. Resting spore formation took place in cells of all sizes and at all temperatures at which the species grew vegetatively (2–15° C). The L. danicus life cycle is probably unique among diatoms. Nitrogen depletion induced sexuality in the entire culture at 10 and 15° C if the cell diameter was narrow (3–8 μm). Auxospore formation was followed by resting spore formation directly within the auxospore. In C. diadema, as in most centric diatoms, resting spores are not an obligate part of the life cycle, but they are in L. danicus. Resting spore formation is a versatile adaptive response in C. diadema, depending only on nitrogen depletion, although promoted by low temperatures. In L. danicus the linkage to the sexual process sharply limits conditions under which resting spores can form.     

HIGH‐RESOLUTION MAGIC ANGLE SPINNING NMR ANALYSIS OF WHOLE CELLS OF CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE) AND COMPARISON WITH 13C‐NMR AND DISTORTIONLESS ENHANCEMENT BY POLARIZATION TRANSFER 13C‐NMR ANALYSIS OF LIPOPHILIC EXTRACTS1

Lipid composition in extracted samples of Chaetoceros muelleri Lemmermann was studied with ¹³C‐NMR and distortionless enhancement by polarization transfer (DEPT) ¹³C‐NMR, resulting in well‐resolved ¹³C‐NMR spectra with characteristic resonance signals from carboxylic, olefinic, glyceryl, methylene, and methyl groups. The application of a DEPT pulse sequence aided in the assignment of methylene and methine groups. Resonance signals were compared with literature references, and signal assignment included important unsaturated fatty acids such as eicosapentaenoic and docosahexaenoic and also phospholipids and glycerols. Results from the extracted samples were used to assign resonance signals in a high‐resolution magic angle spinning (HR MAS) DEPT ¹³C spectrum from whole cells of C. muelleri. The NMR analysis on whole cells yielded equally good information on fatty acids and also revealed signals from carbohydrates and amino acids. Broad resonance signals and peak overlapping can be a problem in whole cell analysis, but we found that application of HR MAS gave a well‐resolved spectrum. The chemical shift of metabolites in an NMR spectrum depends on the actual environment of nuclei during analysis, and some differences could therefore be expected between extracted and whole cell samples. The shift differences were small, and assignment from analysis of lipophilic extract could be used to identify peaks in the whole cell spectrum. HR MAS ¹³C‐NMR therefore offers a possibility for broad‐range metabolic profiling directly on whole cells, simultaneously detecting metabolites that are otherwise not detected in the same analytical set up and avoiding tedious extraction procedures.     

DOES BLUE LIGHT AFFECT THE GROWTH OF CHAETOCEROS PROTUBERANS (BAGILLARIOPHYGEAE)?1

If one wishes to distinguish chromatic effects from irradiance effects on metabolism. it is technically invalid to expose cells lo irradiances of equal photosynthetically available radiation (PAR) unless PAR is absorbed in totality. Therefore, the effects of blue light on growth and cellular concentrations of carbon, protein and carbohydrate of the diatom Chaetoceros protuberans Lauder, (in semi-continuous cultures), were studied by exposing the cells to irradiances of equal photosynthetically usable radiation (PUR), of white (PUR_w) and blue (PUR_b) light. Three average levels: PUR_w=PUR_b=56, 125 and 13 μ m^?2.s^?1 were used in the stated sequence. With increasing PUR the relative concentration of carbohydrate increased in both types of light. The efficiency of this increase was not modified by blue light. The relative concentration of protein remained constant in white light out the efficiency of net protein production improved at the lowest blue light irradiance. The saturation threshold of this chromatic effect was higher in C. proluberans than in the Chlorophyceae. The chromatic change did not affect the average cell doubling rate, calculated over (5 or 6 days) an observation which does not agree with recently published work.     

REJUVENATION OF MELOSIRA GRANULATA (BACILLARIOPHYCEAE) RESTING CELLS FROM THE ANOXIC SEDIMENTS OF DOUGLAS LAKE,MICHIGAN. I. LIGHT MIGROSCOPY AND 14C UPTAKE 1

Resting cells of Melosira granulate (Ehr.) Ralfs were collected from the anoxic sediments of Douglas Lake, Michigan. Sediment containing M. granulata was inoculated into distilled water and incubated in a growth chamber for one week during which observations were made on the cytological differentiation process. Cells classified as “condensed,” i.e. containing a dark brown cytoplasmic mass were identified as resting cells. The differentiation process consisted of a series of gradual cytological changes that included elongation of the cytoplasmic mass and recognition of definable organelles to the point where the cells were non-distinguishable from water column vegetative cells. Differentiating cells accumulated large polyphosphate and lipid granules. However, these granules disappeared just prior to cell division. The complete differentiation or rejuvenation sequence occurred in some cells in less than 24 h. However, not all dormant cells rejuvenated at the same time and it was observed that the lag period for rejuvenation increased with resting cell age (depth of burial in sediments). In the ¹⁴C uptake studies, label was initially observed in condensed state cells. The label gradually progressed to the more differentiated forms. Total carbon uptake during the rejuvenation process was initially lower in the rejuvenating cells, but roughly equal to water column populations after 8 h, indicating a period of high metabolic activity in the rejuvenating cells between 1 and 8 h.     

BLOOMS OF SURF-ZONE DIATOMS ALONG THE COAST OF THE OLYMPIC PENINSULA,WASHINGTON. VI. DAILY PERIODICITY PHENOMENA ASSOCIATED WITH CHAETOCEROS ARMATUM IN ITS NATURAL HABITAT1,2

Microscope observations of chains of Chaetoceros T. armatum T. West, collected, from its natural habitat, at Copalis Beach, Washington, have been made. A regular daily periodicity in the occurrence of cell division stages and length of the chains was found on each occasion (November, February, April, May, August). During the night, short chains of 3 cells predominated. In early morning hours, average chain lengths increased due to cell elongation, and nuclear and protoplast division occurred. This correlated with the time of day when cell masses of C. armatum first appeared at the surface of the water. In the late afternoon, the new silica valves of the daughter protoplasts were formed. Formation of special bristle-bearing end valves effected the separation of long chains into shorter chains composed predominantly of 3 cells. (Cultured material was used to verify some of these stages.) This correlated with the time of day when cell masses disappeared from the water surface and dispersed.     

EXTREMELY HIGH GROWTH RATE OF THE SMALL DIATOM CHAETOCEROS SALSUGINEUM ISOLATED FROM AN ESTUARY IN THE EASTERN SETO INLAND SEA,JAPAN1

Small single‐celled Chaetoceros sp. are often widely distributed, but frequently overlooked. An estuarine diatom with an extremely high growth potential under optimal conditions was isolated from the Shinkawa‐Kasugagawa estuary in the eastern part of the Seto Inland Sea, western Japan. It was identified as Chaetoceros salsugineum based on morphological observations. This strain had a specific growth rate of 0.54 h^?1 at 30°C under 700 μmol · m^?2 · s^?1 (about 30% of natural maximal summer light) with a 14:10 L:D cycle; there was little growth in the dark. However, under continuous light it grew at only 0.35 h^?1 or a daily specific growth rate of 8.4 d^?1. In addition, cell density, chlorophyll a, and particulate organic carbon concentrations increased by about 1000 times in 24 h at 30°C under 700 μmol · m^?2 · s^?1 with a 14:10 L:D cycle, showing a growth rate of close to 7 d^?1. This very rapid growth rate may be the result of adaptation to this estuarine environment with high light and temperature. Thus, C. salsugineum can be an important primary producer in this estuary in summer and also an important organism for further physiological and genetic research.     

CHLOROPHYLL C PIGMENT PATTERNS IN 18 SPECIES (51 STRAINS) OF THE GENUS PSEUDO‐NITZSCHIA (BACILLARIOPHYCEAE)1

The pigment composition of 18 species (51 strains) of the pennate diatom Pseudo‐nitzschia was examined using HPLC. The carotenoid composition was typical for diatoms, with fucoxanthin (the major xanthophyll), diadinoxanthin, diatoxanthin, and β,β‐carotene. However, a diverse array of chl c pigments was observed in the studied strains. All Pseudo‐nitzschia strains contained chl a and chl c₂, traces of Mg‐2,4‐divinyl phaeoporphyrin a₅ monomethyl ester (MgDVP), and traces of a chl c₂–like pigment originally found in the haptophyte Pavlova gyrans. The distribution of chl c₁ and chl c₃ was variable among species (present in seven and 14 species, respectively). Based on chl c distribution, three major pigment types were defined: type 1 (chl c₁ + c₂, four species: P. australis, P. brasiliana, P. multiseries, and P. seriata), type 2 (chl c₁ + c₂ + c₃, three species: P. fraudulenta, P. multistriata, and P. pungens), and type 3 (chl c₂ + c₃, 11 species: P. arenysensis, P. calliantha, P. cuspidata, P. decipiens, P. delicatissima, P. galaxiae, P. mannii, P. pseudodelicatissima, P. subcurvata, P. cf. subpacifica, and a novel Pseudo‐nitzschia species). Type 1 and 2 species also shared the absence of a particular morphological character, the central nodule in the raphe, with the only exception of P. fraudulenta. The implications of such pigment diversity in chemotaxonomy, HAB monitoring, ecology, and phylogeny of Pseudo‐nitzschia species are discussed.     

BIOLOGICAL AND CHEMICAL CHARACTERISTICS OF THE GIANT DIATOM ETHMODISCUS (BACILLARIOPHYCEAE) IN THE CENTRAL NORTH PACIFIC GYRE

Cells of the giant diatom Ethmodiscus Castr. gathered from the upper 15 m were examined for O₂ evolution, nitrate reductase activity (NRA), C and N composition, internal NO concentrations, , and ¹⁵NO, ¹⁵NH , and ³²Si uptake in a series of cruises in the central N. Pacific gyre. The δ¹⁵N (2.56–5.09 ‰), internal NO concentrations (0.0– 11.5 mM NO⁻), and NRA (6.7 ± 4.7 × 10⁻⁴μM NO cell ⁻¹·h⁻¹) were consistent with recent exposure to elevated nitrate concentrations and utilization of deep NO as a primary N source. These results are similar to other diatoms that migrate vertically to the nutricline as part of their life cycle. Rate measures (Si[OH]₄ uptake, NRA, and O₂ evolution) indicated surface doubling times from 45 h to 75 h. Both NO and NH uptake in surface waters were low and inadequate to supply N needs at surface NO and NH concentrations. Our results suggest a partitioning in nutrient acquisition, with N acquired at depth and C and Si acquired at the surface. Doubling rates were two to three times higher than predicted from cell volume and C content models. These data are consistent with the observed elemental content being lower than expected because of the dominance of cell volume by the vacuole. Our calculations suggest that Ethmodiscus contributes little to the biogeochemistry of the upper water column via upward nutrient transport. Although reported as a paleo-upwelling indicator, thisevidence suggests that Ethmodiscus has adapted to the nutrient-poor open ocean by a vertical migration strategy and has biological characteristics inconsistent with a upwelling indicator.     

3种北美冷杉的核型研究

本文首次报道３种北美冷杉Ａｂｉｅｓ ａｍａｂｉｌｉｓ、Ａ．ｇｒａｎｄｉｓ和Ａ．ｌａｓｉｏｃａｒｐａ的根尖体细胞核型、染色体参数及核型模式图。核型公式分别是Ｋ（２ｎ）＝２４＝１６ｍ（４ＳＣ）＋８ｓｍ、１４ｍ（２ＳＣ）＋１０ｓｍ和１８ｍ（４ＳＣ）＋６ｓｍ,染色体相对长度组成为２ｎ＝２４＝２Ｌ＋１２Ｍ２＋６Ｍ１＋４Ｓ、２Ｌ＋１２Ｍ２＋８Ｍ１＋２Ｓ和２Ｌ＋８Ｍ２＋１２Ｍ１＋２Ｓ。均为２Ａ核型类型。文中还讨     

SOME ASPECTS OF MORPHOLOGICAL VARIATION IN STEPHANODISCUS NIAGARAE (BACILLARIOPHYCEAE)1

Valves of S. niagarae var. niagarae Ehr. and S. niagarae var. magnifica Fricke from geographically dispersed sediment and plankton collections were observed by light microscopy and scanning electron microscopy (LM and SEM). Measurements made by LM can be arranged so that means and ranges of diameter, areolar density, or strial density intergrade from one population into the next. Mean diameter is negatively related to increasing areolar and strial densities. No unique features observable by SEM distinguish the two described varieties. Thus, S. niagarae var. magnifica, having large diameter valves with low areolar and strial densities, may represent one end of a trend in overall variation in S. niagarae. At the opposite extreme are the populations with small valves and high areolar densities which are often erroneously referred to as S. astraea. Type material of S. niagarae lies intermediate to these forms. Three populations considered in this study have distinct morphological characteristics. Valves from Yellowstone Lake sediments have spine placements distinctly different from valves of all other populations. Specimens from Lake Superior have nearly flat central areas. Ribs of valves from Grand Traverse Bay (Lake Michigan) are covered with granules.