摘要:

SUMMARY1Hypogeous fungi are those soil fungi which produce macroscopic fruit‐bodies partially or completely embedded in soil or humus. While showing a superficial similarity correlated with habitat, they include members of the Basidiomycetes, Ascomycetes and Phycomycetes.2The edible truffles have been known from very early times, and speculations as to their nature are found in Greek and Roman literature. Other groups, which are not edible, were described later. The monographs of Vittadini (1831, 1842) and L. R.&C. Tulasne (1851) are the starting‐point for all modern work on these fungi.3The true truffles and various related forms are included in the Tuberales and show obvious relationship with the Pezizales. Young fruit‐bodies of the more complex species, such asTuber, resemble mature ones of the simpler forms, such asGyrocratera, or of the Pezizales. The group is best divided into four subfamilies (Knapp, 1950‐2): Pseudotuberaceae, Geneaceae, Eutuberaceae and Terfeziaceae.4The hart's truffle,Elaphomyces granulatus, has long been known and was valued as an aphrodisiac. Together with other species of the genusElaphomyces, the relatedAscosclerodermaand the AustralianMesophelia, it is included by Dodge (1929) in the family Elaphomycetaceae of the Plectascales.5The hypogeous Basidiomycetes, which were formerly grouped in the familyHypogeous fungiHymenogastrales (or Hymenogastraceae of some authors), have not yet been satisfactorily classified owing to lack of detailed knowledge of fruit‐body development for all except a few species. It is clear, however, that they do not form a single homogeneous group. They may be provisionally divided into the groups Proto‐gastraceae, Hysterangiaceae, Rhizopogonaceae (or Melanogastraceae), Hymenogastraceae and Hydnangiaceae. The epigeous Secotiaceae probably provides a link with the Agaricaceae, and relationships have been traced between the Hydnangiaceae and theRussula‐Lactariusgroup of agarics and between the Hysterangiaceae and the epigeous gasteromycetous group of the Phallales.6The genusEndogoneformerly included species producing zygospores, chlamydospores or sporangia in definite fruit‐bodies. The method of zygospore production is such that there is no doubt that the zygosporic species are best classified as a separate family, the Endogonaceae, within the Mucorales. The chlamydosporic species are of similar general structure and are probably related to the zygosporic forms, since Thaxter (1922) demonstrated the presence of both types of spore within the same fruit‐bodies ofE.fasciculata.Cultural studies by Kanouse (1936) showed that a zygosporic species (E. sphagnophila) produced sporangia resembling those ofMucor.Kanouse suggested that the forms producing sporangia aggregated in loose hyphal wefts, formerly attributed toEndogone, are in fact more closely allied toMortierellaand should be transferred to the new genusModicellaand excluded from the Endogonaceae. Some other little‐known genera producing chlamydospores aggregated in definite fruit‐bodies are included in Endogonaceae by Thaxter.7Most hypogeous fungi are found only in woodlands. Fruit‐body formation is, in general, favoured by a light, well‐drained soil, with a slightly alkaline hydrogen‐ion concentration, although a few species occur in acid soils. Growth is inhibited or checked by extreme cold or by drought.8Considerable circumstantial evidence exists for a mycorrhizal association between many, but not all, species of hypogeous fungi and trees or other plants. In a few examples there is definite proof. Other species are probably true parasites on roots of higher plants.9Very few species have been isolated in artificial culture and very little is known of their nutritional requirements. Those which have been investigated resemble other mycorrhizal species in requiring organic nitrogen and vitamin B1.10Attempts have been made, particularly in France, to stimulate the development of edible truffles in known truffle‐grounds and to establish them in new places. Some success has been claimed by inoculation of the soil of young tree plantations both with soil from known truffle grounds and with pieces of mature fruit‐bodies.11No attempts to produce mycelium by germinating spores of hypogeous fungi have so far been successful. Various authors have depicted what they claim to be early stages of germination, some of which

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1955.tb01578.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

SUMMARY1To most authors the study of nerve terminations in mammalian skin has been an exercise in descriptive morphology. A single histological technique was usually considered adequate and presumably impeccable, for observations resulting from different techniques were not compared and the possibility of artefacts was not considered.2The literature is thus excessively large and full of controversies over histological minutiae. It also contains theories concerning the organization of the nervous system which are at variance with the results of physiological observations.3The work of a few authors is in striking contrast, but their observations have either been ignored or discounted.4The recent discovery that nerve fibres can be seen in fresh specimens of cornea under phase‐contrast conditions has led to the development of new neuro‐histological techniques. These display nerve fibres and their terminals selectively in skin. They appear in an undistorted state and are virtually free from artefacts.5The use of new techniques has shown that it is characteristic of all nerves entering mammalian skin to terminate in an arborization of fine (<1μin diameter), naked, axoplasmic filaments which probably end freely. Ensheathed stem fibres give rise to unencapsulated nerve endings in all skin strata, and terminals from neighbouring stem fibres overlap and interdigitate extensively. Axoplasmic filaments terminate in the cellular layers of the epidermis and in the dermis but in no specific relation to the capillaries. They are found in relation to the myoepithelial and gland cells of sweat glands, and in relation to the adventitia and media of blood vessels.6In hairy skin there are in addition to the unencapsulated nerve endings nerves which end specifically in relation to hair follicles. Ensheathed myelinated stem axons give rise to two distinct and separate series of arborizations of fine, naked, axoplasmic filaments which lie at right angles one within the other. The outer series encircle the hair lying among the cells of the middle layer of the dermal coat. The inner series lie among the cells of the outer root sheath parallel to the hair shaft. No encapsulated nerve endings are seen in hairy skin.7In glabrous skin and mucous membranes, such as the lip, anus and glans penis, there are, in addition to the unencapsulated nerve endings, numerous encapsulated nerve endings. They are of different sizes and shapes, and the ensheathed myelinated stem fibre or fibres which enter the capsule pursue a more or less tortuous course. They then give rise in all cases to an arborization of fine, naked, axoplasmic filaments which end freely among the capsular cells in planes roughly parallel to the surface layer of cells.8In the light of these findings a re‐analysis of the observations and, in particular, the diagrams in the literature, forces one to the conclusion that the actual facts which have been reported by various authors have more in common than would have been supposed from a perusal of their summaries and conclusions.9As the result of comparing observations on the innervation of skin following the use of numerous different techniques including those involving the use of hyaluronidase, it is now possible to reinterpret the observations in the literature. A standard for histological comparison now exists and it is also possible to determine what is and what is not an artefact, and what a distorted and disrupted nerve fibre or terminal really looks like.10If the literature is reinterpreted in this way, the points concerning the innervation of mammalian skin which emerge correspond both to those described by a few authors whose work is usually ignored or discounted, and to those described by Weddellet al.(1954) using the improved neurohistological techniques.11If this is so, then we are forced to the conclusion that there are not and never have been any purelyhistologicalgrounds on which to erect theories of cutaneous sensibility based on the existence of four primary modalities, touch, warmth, cold and pain, operating within the ‘law of specific nervous energies’. Furthermore, there is not and never really has been convincing histological evidence for the commonly accepted statement that morphologically specific nerve endings subserve each of the primary modalities of cutaneous sensibility.12Our observations suggest that the morphology of nerve terminals in mammalian skin should be studied from the point of view of their functions as transducers of stimuli (mechanical, thermal or chemical) into propagated action potentials rather than taxonomically.This work was made possible by a grant from the Rockefeller Foundation which is gratefully acknowledged. Our best thanks are also due to Miss C. Court for her careful and accurate execution of the ill

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1955.tb01579.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

摘要:

SUMMARY1In a mammal such as a sheep there is a foetal double circulation and an adult double circulation.2Both double circulations have as common factors: (a) separate return of oxygenated and deoxygenated blood to the heart, (b) anatomical separation (partial or complete) of the two streams of blood during their passage through the heart, (c) separate pathways by which the two streams leave the heart.3Amongst the fishes, only in Dipnoi does the pulmonary vein enter a separate portion of the atrial division of the heart.4This pulmonary vein develops in a very similar way to that in which the corresponding vein of a mammal develops.5In the Tetrapoda a completely divided heart is found only in Mammalia, Aves and Crocodilia; partial division is met with in other reptiles and in Amphibia. No living amphibian has an interventricular septum.6The heart of the lung‐fishLepidosiren, in the possession of partial inter‐auricular and interventricular septa, shows an amount of division greater than that of any living amphibian.7The hearts of Dipnoi differ from those of other vertebrates in the nature of the ‘valve’ in the auriculo‐ventricular canal.8The interpretation of the reptilian heart has given rise to much controversy. The ventricle is primarily divided into ventral and dorsal cavities. These cavities probably correspond to the right and left cavities in a lung‐fish. The dorsal cavity becomes subdivided by a secondary septum; it is this secondary septum which in crocodiles and birds becomes the definitive interventricular septum.9The similarity of the four‐chambered hearts of birds and mammals is misleading. In mammals the interventricular septum is the primary septum; in birds it is formed from the secondary septum which is met with in some reptiles.10The foregoing conclusion, reached by Goodrich as the result of comparative studies, is supported by the modes of development of the septa.11Mammalian and avian hearts also show differences in the mode of development of the atrial septum and the foramina in it.12The alinement of the chambers during the development of the heart ofLepidosirenresults in close approximation of the interventricular septum to both the interatrial septum and the septum of the conus.In higher vertebrates the alinement is not so perfect, in that the base of the bulbus (conus) is far to the right of the interventricular septum. The final development of these septa is different in mammals and birds.13The conus, which in Teleostei, some Elasmobranchii and Dipnoi tends to lose its contractile properties, becomes progressively reduced in the higher vertebrates. Eventually it is partially incorporated into the right ventricle and also forms part of the roots of the aorta and pulmonary artery.14The splitting of the conus into two paths in the Theropsida and three in the Sauropsida is of great significance.15The association of the carotids with the right systemic arch in the sauropsids and with the left in theropsids is equally significant.16The persistence of the left systemic arch in reptiles may be explained with reference to the relative volumes of the systemic and pulmonary circulations and may also be related to the embryonic circulation.17The blood supply to the heart muscle itself is also of great importance, and a comparison of the coronary systems of fishes with higher vertebrates shows that the evolution of this system has proceeded hand‐in‐hand with the division of the heart.18The reduced coronary system of amphibians, taken together with the absence of a ventricular septum and viewed in the light of current ideas concerning the evolutionary position of Recent Amphibia, suggests that the heart of these animals is to be regarded as highly specialized.19As has repeatedly been made clear, the Dipnoi are not to be considered as ancestral to the tetrapods, yet they are the nearest group of fish to the early land vertebrates of which the soft parts are available for study. The hearts of dipnoans possess several features which demonstrate their specialized nature; nevertheless they also show other features which cannot all be accounted for by convergence. In this framework an attempt has been made to assess the evolutionary importance of the dipnoan ventricular septum, and it seems to be more in agreement with the facts to assume that a ventricular septum was present in the heart of the first tetrapods than to imagine that the condition seen in living amphibians represents an ancestral one.20If the first tetrapods possessed an interventricular septum homologous with that of Dipnoi, then this septum has been lost in Recent Amphibia. It was replaced by a secondary septum in the sauropsid reptiles which gave rise to the birds, and so this secondary septum forms the interventricular septum of birds; but the original septum was apparently retained by the theropsid reptiles and so became the interventricular sept

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1955.tb01580.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1955.tb01581.x

出版商:Blackwell Publishing Ltd    

年代:1955

数据来源: WILEY