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During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO(2)) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO(2) seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO(2) gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO(2) cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO(2) due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO(2) transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO(2) uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO(2) anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO(2) anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018. This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

The pecten oculi is a highly vascularized and pigmented organ that overlies the optic disc and projects into the vitreous body in the avian eye. First reported over 300 years ago, its function(s) remains a puzzle to ornithologists, ophthalmologists and anatomists. Morphometric study of this unique organ was undertaken in birds exhibiting apparently different visual acuities, namely two species of diurnal birds (the ground-dwelling domestic fowl Gallus gallus var. domesticus and a highly active predator bird, the black kite (Milvus migrans) and a nocturnal bird (the spotted-eagle owl Bubo bubo africanus). The volume of the owl's eye was 4.8 and 2.2 times larger than that of the fowl and the kite, respectively. However, the pecten of the fowl consisted of more pleats (16–18) compared to the kite (12–13) and the owl (5–6). The volume of the pecten of the kite was 1.4 and 2.7 times larger than that of the fowl and the owl, respectively (P < 0.05). Similarly, the surface area of the pecten of the kite was 2.6 and 4 times larger than that of the fowl and owl, respectively (P < 0.05). The volume density of blood vessels (lumen and wall) in the pecten of the kite, fowl and owl comprised 67.7%, 66.9% and 62.6%, respectively, the pigmented tissue constituting the rest. Both the volume density and the volume of the blood in the pecten were higher in the diurnal birds (kite, fowl) than the owl (P < 0.05). The surface area of the capillary luminal surface was 1.7 and 5.3 times higher in the kite than in the fowl and the owl, respectively (P < 0.05). These results suggest that the functional morphology of the pecten correlates with the life-style of the bird and with functional need, and lends further support to the nutritive role of the pecten.

The structure of the capillary endothelium in the pecten oculi of the domestic fowl was investigated by scanning and transmission electron microscopy. Scanning electron microscopy results demonstrated the existence of a vast array of irregular microplicae that projected from the luminal surface of the capillary endothelium. In between these microplicae were numerous crevices. The microplicae were closely packed and showed no preferred orientation regarding either the longitudinal or transverse plane of the capillaries. Transmission electron microscopy revealed the section profiles of the microplicae: their tortuity, branching, interdigitations and the magnitude of the crevices contained. The endothelial cytoplasm exhibited a few mitochondria and micropinocytotic vesicles. The apparent set-up of the luminal plasmalemmal infoldings seemed to be designed for effecting impedance to the pectineal blood flow and thereby facilitating passive permeation of blood-borne nutrients to the inner neural retina. The reasons of such passive transport operation mediated by the endothelial microplicae of the avian pecten oculi are discussed in the perspective of the existing literature.

The traditional model that teeth are lost due to caries early in life and periodontitis later has been challenged by recent studies. Randomly selected Air Force records were reviewed for the reasons for extractions. Between the ages of 20 to 50, the rate of loss due to caries declined from 0.11 to 0.03, whereas the rate due to periodontitis increased from 0 to 0.34. This study supported the traditional model that tooth loss due to caries decreases with age and that periodontitis is the major cause of loss later in life.

The pecten oculi is a structure peculiar to the avian eye. Three morphological types of pecten oculi are recognized: conical type, vaned type and pleated type. The pleated type has been well studied. However, there exists only scanty data on the morphology of the latter two types of pectens. The structure of the vaned type of pecten of the ostrich, Struthio camelus was investigated with light and electron microscope. The pecten of this species consists of a vertical primary lamella that arises from the optic disc and supports 16-19 laterally located secondary lamellae, which run from the base and confluence at the apex. Some of the secondary lamellae give rise to 2 or 3 tertiary lamellae. The lamellae provide a wide surface, which supports 2-3 Layers of blood capillaries. Pigmentation is highest at the distal ends of the secondary and tertiary Lamella where blood capillaries are concentrated and very scanty on the primary and the proximal ends of the secondary lamella where the presence of capillaries is much reduced. In contrast to the capillaries of the pleated pecten, the endothelium of the capillaries in the pecten of the ostrich exhibits very few microvilli. These observations suggest that the morphology of the pecten of the ostrich, a flightless ratite bird is unique to the pleated pecten and is designed to meet the balance between optimal vision and large surface area for blood supply and yet ensuring it is kept firmly erect within the vitreous.

The intestinal morphology of 7-week-old pigs was investigated by light (LM) and scanning electron microscopy (SEM). The piglets were fed either a semisynthetic or a cereal-based diet. The shapes of the intestinal villi and crypts of the duodenum, jejunum and ileum were examined. The villi were predominantly tongue-shaped. In the duodenum they were also ridged, branched and folded, and in the jejunum they were also leaf-like and ridged. At places with lymph follicles, the surface of the ileum was rugged with meandering fold-like villi. The crypts of the three segments of the small intestine were mainly coiled and sometimes branched. A novel morphometric evaluation method was introduced using the enlargement factors of each villus and crypt surface. The enlargement factor for the villus surface of the duodenum, jejunum and ileum was 3.13, 3.72 and 2.71, respectively. The factor for the crypt surface of the duodenum, jejunum and ileum was 9.07, 8.94 and 6.53, respectively. Furthermore, the relative proliferation rate and the epithelial renewal index were calculated for the first time. The relative proliferation rate of the duodenum, jejunum and ileum was 32.88, 34.78 and 50.77 proliferations per mm crypt perimeter, respectively. The diets consumed had an influence on the epithelial renewal index being higher for piglets fed the cereal-based diets.

The luminal surface of the pecten oculi of the black kite (Milvus migrans), a diurnally active bird of prey, was examined by scanning electron microscopy. In this species the blood vessels are generally of two types, the small-calibre capillaries and the large-calibre afferent and efferent vessels. The luminal surface of the efferent blood vessels possesses a few low microplicae. Conversely, the luminal surface of the afferent blood vessels is characteristically smooth except at the cell junctions and at the point of entry into the capillaries. The cells junctions are marked by low ragged ridges while the luminal surface is studded with low sparse pleiomorphic microprojections at the point of capillary emergence. The luminal surface of the blood capillaries is characterised by a labyrinth of closely disposed microplicae that projects into the lumen. These microplicae show no particular orientation with respect to either the longitudinal or transverse axis of the capillary. Instead, they are diffusely orientated. It is conjectured that such a heterogeneous design of the endothelium in the blood vessels of the pecten oculi has developed in order to augment the role of the pecten in the transport of nutrients to the avascular neural retina by an energy saving diffusion process. The process through which the design of the microfolds affects haemodynamics and their putatite role in facilitating the delivery of nutrients are discussed in the perspective of the available data.

The structure of the capillary endothelium in the pecten oculi of the domestic fowl was investigated by scanning and transmission electron microscopy. Scanning electron microscopy results demonstrated the existence of a vast array of irregular microplicae that projected from the luminal surface of the capillary endothelium. In between these microplicae were numerous crevices. The microplicae were closely packed and showed no preferred orientation regarding either the longitudinal or transverse plane of the capillaries. Transmission electron microscopy revealed the section profiles of the microplicae: their tortuity, branching, interdigitations and the magnitude of the crevices contained. The endothelial cytoplasm exhibited a few mitochondria and micropinocytotic vesicles. The apparent set-up of the luminal plasmalemmal infoldings seemed to be designed for effecting impedance to the pectineal blood flow and thereby facilitating passive permeation of blood-borne nutrients to the inner neural retina. The reasons of such passive transport operation mediated by the endothelial microplicae of the avian pecten oculi are discussed in the perspective of the existing literature.

The traditional model that teeth are lost due to caries early in life and periodontitis later has been challenged by recent studies. Randomly selected Air Force records were reviewed for the reasons for extractions. Between the ages of 20 to 50, the rate of loss due to caries declined from 0.11 to 0.03, whereas the rate due to periodontitis increased from 0 to 0.34. This study supported the traditional model that tooth loss due to caries decreases with age and that periodontitis is the major cause of loss later in life.

The conjunctiva of the dog has a smooth surface on the inside of the upper and lower lid and of the bulbus oculi. In these areas the conjunctiva is covered by a stratified squamous epithelium, the polygonal surface cells of which have microvilli and microplicae which are different in number and show a great variety of shapes. In the passage towards the fornix conjunctivae a stratified cuboidal epithelium is to be discerned. In the fornix itself, the conjunctiva is arranged in small folds which are protruded by goblet cells and the openings of lacrimal glands. Here a stratified cuboidal or columnar epithelium can be observed which at the electron microscopic level shows in all epithelial layers--mostly however in the stratum superficiale--morphological signs of enhanced metabolic activities. The bulbar surface of the third eyelid which is covered by a stratified squamous epithelium has a three-dimensional moulded pattern of pads and grooves. The structure of the conjunctival epithelium to some extend is age dependent.

The purpose of this paper is to demonstrate the stereoscopic structure of the papillary body of the proventricular mucous membrane in the sheep and the goat. This papillary body hitherto has only been known from histological sections. — Tissue specimen were taken from freshly killed animals and put into 0.3% acetic acid, in order to let the epithelium peal off. The investigation was carried out with the scanning electronmicroscope. At places where the mucous membrane has a smooth surface, the papillary body consists of slender papillae and in the other proventricular portions it consists of cone-, crest- or comblike propria elevations.

Light and electron microscopic investigations on the Mg++- and Ca++-activated ATPase of sheep and goat dorsal root ganglion have been carried out. Reaction products occur on plasma membranes and interfaces between neurons and sheath cells, between adjacent sheath cells and on the surface of unmyelinated fibers. Cytoplasmic protrusions of ganglion cells and numerous surface increasing invaginations of sheath membranes form close connections between neurons and sheath cells.

The purpose of this scanning electronmicroscopical study was to describe the structure of the lamina propria of the ruminal mucosa in calves on different diets. The surface epithelium was removed with 0.3 % acetic acid. The exposed lamina propria showed structural differences, both macroscopically and microscopically in the different dietary groups. At the submicroscopic level, however, no differences were observed.

The distribution of somatostatin cells was investigated immunohistochemically in the epithelium of the abomasal mucous membrane of sheep and goats. Tissue samples were taken from different areas at the lesser and greater curvature of the glandular stomach. More somatostatin cells per 0.5 mm2 were found in sheep than in goats, predominantly in the pyloric gland region. In the pyloric area of both species the mucosa in the greater curvature contained more immunoreactive cells than the one in the lesser curvature. A few somatostatin cells with basal cytoplasmic processes of the ‘open type’ were observed over the entire abomasal mucosa.

Light- and electron microscopic investigations were conducted on the epithelium of the area glandulae gastricae propriae of the abomasum, using material of 12 East African game ruminants of nine species. The members of the main feeding categories (Hofmann, Stewart 1972): concentrate selector, roughage eater and intermediate feeder did not differ much in the ultrastructure of the fundic stomach epithelium but showed greater differences with respect to the height and shape of the glandular tubules and the arrangement of the epithelial cell types. Specifically the following cell types were observed: mucoid cells, chief cells, parietal cells, seven different endocrine cells, tuft cells and two types of migrating cells. In some epithelial celltypes of the concentrate selector dikdik, cristalloid cytoplasmic inclusions were found.

The conjunctiva of the domestic ruminants is covered by several kinds of epithelia which intergrade smoothly. There is a stratified nonkeratinized squamous epithelium which covers the greater part of the conjunctival mucous membrane. There is a stratified cuboidal, stratified mixed and occasionally a stratified goblet cell epithelium, localized mainly in the area of the fornix conjunctivae. In the area of the "serrated crest" of the nictitating membrane as well as the transition between conjunctiva and cornea, but also in the other conjunctival regions, the propria mucosae and the epithelium contains a few or numerous migrating lymphoid cells.

Light- and electronmicroscopic and some histochemical investigations on the major excretory ducts of pancreas and liver was carried out on 24 adult chicken. The epithelium of both ducts was shown to include: cells with apical secretory granules, non-differenciated duct cells, ciliated cells and migrating cells. In addition the epithelium of the pancreatic ducts included goblet cells. The distal plasmalemm and the microvilli are covered with surfacecoat, which like the secretory granules produces precipitate with PA-silver. This area of the cell also shows a strong reaction to M++ and Ca++ activated ATPase.

Light and electron microscopic investigations on the Mg++- and Ca++-activated ATPase of sheep and goat dorsal root ganglion have been carried out. Reaction products occur in plasma membranes and interfaces between neurons and sheath cells, between adjacent sheath cells and on the surface of unmyelinated fibers. Cytoplasmic protrusions of ganglion cells and numerous surface increasing invaginations of sheath membranes form close connections between neurons and sheath cells.

The purpose of this study was to provide information to aid USAF dental Clinics in their selection of the best dental visible-light curing unit for their requirements. Twelve units were compared against a set of criteria comprising the most desirable and necessary features. Each unit was also field tested for a user's comparison. Most units were found to be similar in their features, but depth of cured varied widely from unit to unit. All of the tested units essentially performed the tasks for which they had been designed. The selection of a visible-light curing unit depends on the needs of the respective dental clinic.

Light-and electron-microscopic and some histochemical investigations on the epithelium or the ductus pancreaticus major were carried out in sheep. At least six different cell types are recognizable: (1) nondifferentiated duct cells; (2) cells containing apical secretory granules; (3) goblet cells; the mucosubstances of type 2 and 3 are PAS- and Alcian-blue-positive, also reacting wih methenamine silver; (4) ciliated cells, containing a single cilium with the microtubular pattern 9+2; (5) tuft cells with extremely long and wide microvilli and a pear-shaped cell body; (6) migrating cells, mainly lymphocytes and some assumed eosinophils, showing reaction to Mg++-activated ATPase.

The surface of the conjunctiva was investigated in goats, sheep and bovines. The lid-facing surface of the nictitating membrane carries a serrated crest. At a low magnification the areas covered by a stratified squamous epithelium appear as a mosaic. In the superior and inferior conjunctival fornices the mucous membrane has a uniform appearance. Areas of goblet cells have an irregular appearance. Four functional stages can be observed in the goblet cells. At a high magnification the superficial cells of the palpebral and bulbar conjunctiva are covered by microplicae. In the fornix conjunctival microvilli project over the superficial cells.

The celltype here described, was discovered during an investigation of the epithelium of the main excretory ducts of the liver and the pancreas, as well as the conjunctiva, the organ of Jacobson and the glandular stomach of domestic ruminants. This s.c. Tuft cell in every case was shown to contain the following main characteristics: 1. Pearshape with a narrow apex, and a wide and round base. 2. Large spherical or ovoid nucleus. 3. Cellapex with unusually wide microvilli extending above the surface of the epithelium. 4. Filamentbundels of the microvilli radiating to the perinuclear space. 5. Electrondense small and big granules in the distal part of the cell or in the area around the nucleus. Tuftcells are possibly receptor cells with special additional functions that have adapted to various epithelial types.

Ruminal lymphvessels from the goat were investigated with light- and electronmicroscope after blockade of the lymphdrainage and vascular perfusion by means of yellow fix solution. The lymphvessels of the ruminal wall do not originate directly from below the epithelium but from the deeper layers of the Propria mucosae. As far as ruminal papillae are concerned, lymphatic vessels are only to be found at their base. All lymphvessels consist of a basement membrane and an endothelium. Only the ones which are situated in the Subserosa or in the musculature of the wall are provided with lymphatic valves.

The vascular system of the stomach of the chicken was investigated by means of corrosion preparations as well as by light- and electronmicroscopic methods. The main vessels form a) an Intermuscular Plexus the outer longitudinal and inner circular layers of the muscle wall in the glandular stomach and b) a Subserous Plexus in the muscular stomach. In the glandular stomach the Interglandular Parietal Arterial Plexus I, situated below the Lamina muscularis mucosae I arises from the arteries which pass through gaps in the muscle wall. This Plexus I produces another plexus, the Interglandular Arterial Plexus II, located on top of the Lamina muscularis mucosae I. Both arterial plexuses are accompanied by venous plexuses, which convey the blood into a Subglandular Venous Plexus. -The vessels of the muscular stomach provide the predominant supply of blood to the muscle wall. The mucous membrane of the muscular stomach is vascularized far less than the one in the glandular stomach. -The hemodynamic relationships of the vessels of the hen's stomach and the significance of the fine structure of the subepithelial capillaries and venules for the exchange of materials are discussed.

The basal cells of all types of epithelia in the domestic ruminants have a smooth surface in their proximal part or are furnished with branched cytoplasmic projections. The cytoplasm of many basal cells contains a few or many micropinocytotic vesicles, which can be arranged in a moniliform manner. The intermediate cells as well as the cells of the stratum superficiale - with the exception of the uppermost layers of the stratified squamous epithelium - are characterized by the presence of a great number of membrane-bound granules. Microvilli which project over the uppermost epithelial cells only occasionally contain a filamentous internal structure. The apical closure of the epithelium is preferentially formed by zonulae occludentes (tight junctions) with maximally 2-3 tight junction seals, they are followed proximally by 1-2 desmosomes. Zonulae adhaerentes can only rarely be observed. The nervous supply of the conjunctival epithelium which is best developed in the bulbusfacing side of the nictitating membrane is brought about by sub- and intraepithelial nerve-endings.

The distribution of somatostatin cells was investigated immunohistochemically in the epithelium of the abomasal mucous membrane of sheep and goats. Tissue samples were taken from different areas at the lesser and greater curvature of the glandular stomach. More somatostatin cells per 0.5 mm2 were found in sheep than in goats, predominantly in the pyloric gland region. In the pyloric area of both species the mucosa in the greater curvature contained more immunoreactive cells than the one in the lesser curvature. A few somatostatin cells with basal cytoplasmic processes of the 'open type' were observed over the entire abomasal mucosa.

The mucous membrane of the Cloaca was investigated light and electronmicroscopically in 20 hens. Some histochemical investigations and a reabsorption test were carried out. The surface of the Coprodaeum is being formed by villi and deep crypts. The former disappears gradually within the Urodaeum. The latter crypts can be found down to the Proctodaeum. The epithelium of the Coprodaeum and Urodaeum consists of goblet cells and highprismatic cells containing secretory granules. The Proctodaeum can be subdivided into three parts. A cranial, containing the same epithelium as the Coprodaeum, a middle with a two layered highprismatic epithelium and a caudal part with a multilayered squamours epithelium. The columnar cells of all parts of the cloaca show a strong reaction to acid phosphatase and ATPase, whereas alkaline phosphatase is almost negative.

During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO2) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO2 seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing to investigate how ecosystem flux anomalies impacted spatial CO2 gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO2 cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO2 due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO2 transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO2 uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO2 anomaly observed in 2018 were compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO2 anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018.This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO2) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO2 seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing to investigate how ecosystem flux anomalies impacted spatial CO2 gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO2 cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO2 due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO2 transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO2 uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO2 anomaly observed in 2018 were compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO2 anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018.This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.