■ ■ ■■ : ■ ,,, .,}■{,, *;[;;._ :.'.;; Cambridge Botanical Handbooks Edited by A. C. Seward and A. G. Tansley FUNGI ASCOMYCETES, USTILAGINALES, UREDINALES CAMBRIDGE UNIVERSITY PRESS C. F. CLAY, Manager LONDON" : FETTER LANE, E.C. 4 LONDON: H K. LEWIS AND CO., Ltd., 136, Gcmer Street, W.C. 1 LONDON : WHELDON & WESLEY, Ltd., 28, Essex Street, Strand, W.C. 2 NEW YORK : THE MACMILLAN CO. BOMBAY 1 CALCUTTA MACMILLAN AND CO., Ltd. MADRAS J TORONTO : THE MACMILLAN CO. OF CANADA, Ltd. TOKYO : MARUZEN-KABUSHIKI-KAISHA ALL RIGHTS RESERYED PALEOMYCES ASTEROXYLI from the Old Red Sandstone, Muir of Rhynie, Aberdeenshire, Kidston and Lang after FUNGI ASCOMYCETES, USTILAGINALES, UREDINALES BY Dame HELEN GWYNNE-VAUGHAN, (formerly h. c. I. fraser) D.B.E., LL.D., D.Sc, F.L.S. PROFESSOR OF BOTANY IN THE UNIVERSITY OF LONDON AND HEAD OF THE DEPARTMENT OF BOTANY, BIRKBECK COLLEGE L1P3ARY NEW •. ■ 8017 N..CAL GAKDEN CAMBRIDGE AT THE UNIVERSITY PRESS 1922 QK&03 PREFACE IT is impossible to study the Fungi without being impressed by the undiminished value of much of the older work, and especially of that of de Ban-, or without recognizing the soundness of his general and very many of his particular conclusions in the light of subsequent investigation. While I have tried to give something approaching adequate references to recent literature, I have thought it superfluous to name the more general works of those earlier authors who are quoted in de Bary's Comparative Morphology of the Fungi, Mycetozoa and Bacteria and elsewhere. By such investigations the foundations of modern mycology have been laid and their discoveries have passed into the groundwork of our knowledge. The intention of the following pages is to present the fungus as a living individual: the scope is mainly morphological, but, in dealing with objects so minute, morphology passes insensibly into cytology. The introduction deals with fungi in general ; the special part of this volume is limited to the consideration of the Ascomycetes, Ustilaginales and Uredinales. The manuscript was completed early in 191 7, but an endeavour has been made to bring it up to date. The majority of the illustrations are drawn from published researches, and I have to thank those authors who have given me permission to copy their figures. Illustrations, the source of which is not stated, are original. In the case of original figures the magnification and the authority for the species are given ; this has also been done in other cases whenever the information was available. I am grateful to many past and present students for specimens and information ; to Miss W. Page for figure 112; to Miss H. Tayler for reading proofs; to Mr Charles Dobb for valuable help in the preparation of figures; to Mr E. S. Salmon for advice on the section dealing with specialization of parasitism ; and especially to my friends Miss E. J. Welsford and Mr J. Ramsbottom for assistance in a number of ways. The earlier written parts of the book, and consequently the whole, owe much to the unfailing interest and wise criticism of my husband. CT> London, >— September, 1921 H. C. I. CAVYNNE-VAUGHAN. COXTHXTS INTRODUCTION GENERA1 Vegetative Structure . Sexual Reproduction . Spores and Spore Mother-cells Accessor}- Spores Morphology of the Spore Classification SAPROPHYTISM, PARASITISM AND SYMBIOSIS Saprophytism . Saprophytes on Wood Saprophytes on Soil Coprophilous Fungi Fungi on Fatty Substrata Fungi producing Alcoholic Fermentation Soot Fungi . Parasitism Facultative Parasites Obligate Parasites Symbiosis .... Endotrophic Mycorhiza Exotrophic Mycorhiza SPECIALIZATION OF SAPROPHYTISM AND PARASITISM Heteroecism Biological Species REACTK >NS TO STIMULI . Chemotropism I lydrotropism Aerotropism and Osmotropism Phototropism Phototaxis . Formative Influei Geotropism . ASCOMYCETES . GENERAL The Ascospores The Ascus . The Ascocarp The Paraphyses The Peridium Alternation of Generations Early Investigators ce of Light PAGE I I I 2 3 4 4 5 6 7 7 7 8 io io 12 13 13 '4 16 16 18 20 22 22 27 27 29 30 30 31 31 31 34 34 34 35 33 38 39 39 40 CONTENTS PAGE Cytology ......... 40 The Fusion in the Ascus .... 4i Fertilization ...... 4i Development of the Ascus .... 42 Meiosis ....... 43 The Third Division in the Ascus 44 Chromosome Association .... 45 The Theory of a Single Nuclear Fusion 45 The Significance of the Fusion in the Ascus 47 Pseudapogamy 48 Spore-Formation 48 Phylogeny . 49 PLECTOMYCETES 55 PLECTASCALES . 56 Endomycetaceae . 57 Saccharomycetaceae 62 Gymnoascaceae . 66 Aspergillaceae 68 Onygenaceae 76 Elaphomycetaceae and Terfeziaceae . 77 Erysiphales 7& Erysiphaceae 79 Perisporiaceae 90 Microthyriaceae . 9i EXOASCALES 9i Exoascaceae 93 DISCOMYCETES . 95 Pezizales . 100 Pyronemaceae IOI Pezizaceae . 107 Ascobolaceae 116 Helotiaceae and Mollisiaceae 122 Celidiaceae, Patellariaceae and Cenangiace; le 124 Cyttariaceae ..... • 125 Helvellales . 127 Rhizinaceae . . 128 Helvellaceae 129 Geoglossaceae • 131 PHACIDIALES 132 Stictaceae 132 Phacidiaceae • 133 HYSTERIALES x33 TUBERALES l35 Tuberaceae . ■ 135 CONTENTS XI PYRENOMYCETES Hypocreales . Nectriaceae . I [ypocreaceae DOTHIDEALES . Sphaeriales Chaetomiaceae Sordariaceae Sphaeriaceae Ceratostc imataceae Amphisphaeriaceae Lophiostomataceae Mycosphaerelfeceae Pleosporaceae Gnomoniaceae Valsaceae Diatrypaceae Xylariaceae . Laboulbeniales BASIDIOMYCETES GENERAL .... HEMIBASIDIOMYCETES USTILAGINALES . Ustilaginaceae Tilletiaceae . PROTOBASIDIOMYCETES . U RE DIN ALES Spores and Sori . Teleutospore Basidiospore . Spermogonium Aecidium Uredosorus . Teleutosorus Omission of Spore Forms Heteroecism Specialization of Parasitism Nuclear Division Nuclear Association Phylogeny . Pucciniaceae Cronartiaceae Melampsoraceae . Coleosporiaceae . GENERAL BIBLIOGRAPHY (B INDEX .... 39 43 43 46 52 53 55 56 58 59 59 r><> fin 61 63 '■4 65 65 7> 83 83 84 84 88 93 96 96 96 97 97 98 200 204 205 207 210 21 1 21 I 213 2 10 219 219 219 220 g with several ( I roups)1 223 I 11 iks and papers dealing with individual fungi or groups of fungi are cited in the Bibliography at the end of (lie relevant section or in foot-notes in the text. CHAPTER I INTRODUCTION The Fungi are parasitic or saprophytic Thallophyta entirely destitute of chlorophyll, and possessing in the very large majority of cases a vegetative portion, the mycelium, made up of filaments or hyphae. The group is a very ancient one, the earliest km iwn undoubted fungi occurring among the remains of Rhynia and Hornia in the Old Red Sandstone of the Muir of Rhynie, Aberdeenshire. This material consists of aseptate hyphae and vesicles which doubtless served the purpose of reproduction (frontispiece)1. Fungal hyphae may be non-septate and coenocytic, or the}' may under- go transverse septation, in which case their constituent cells are either uni- nucleate or multinucleate. Any division other than transverse is extremely rare; it occurs, for example, in the development of certain multicellular (muriform) spores (fig. i), and in the initiation of the perithecium in Strickeria and of the pyenidium in Plcospora and Phoma-. As a rule the hyphae are richly branched ; they elongate by apical growth and usuallyspread loosely through the substratum ; in certain cases, especially in relation to the fructifications of the higher forms, they become woven into a dense mass which gives in section the appearance of a tissue, and is therefore described as pseudoparenchymatous; when fructifications are embedded in such a mass it is termed a stroma; a similar weft of hyphae sometimes give rise to root-like strands of which the best example is the so- called rhizomorph of Armillaria mellea, or to a compact resting body or sclerotium the outer cells of which are modified to form a thick-walled rind, protecting the vegetative mycelium against desiccation. Frequent anastomoses take place between hyphae, either by means of short branches forming loops, bridges or H-pieces, or by means of so-called clamp-connections which join adjacent cells; such arrangements facilitate the passage of food and may, in certain cases, become sufficiently numerous b > form a net-work. The mycelium begins its development as a germ-tube put out from one of the numerous types of fungal spore. Where the spore wall is very thin the wall of the germ-tube may be continuous with it (zoospores), but in the majority of cases the wall of the germ-tube is continuous only with the 1 tidston, K. ami Lang, W. H. On Old Red Sandstone Plants showing Structure from the Rhynie Chen ! rdeenshire, Trans. Roy. Soc. Ed. 1921. - Kempton, F. E. Origin and Development of the Pyenidium, Bot. Gaz. 1919, Ixviii, p. 233. G.-V. I 2 INTRODUCTION [CH. inner layer of the spore wall. In such cases one or more germ-tubes may break through the wall of the spore at spots not previously recognizable, or they may find an exit through special pits or germ-pores formed during the development of the spore. The germ-tube elongates and receives the contents of the spore. In cases where a mycelium is not developed the plant body consists entirely of reproductive structures (Yeast, Archimycetes). The typical fungal protoplast consists of a mass of granular or reticulate cytoplasm, which in the older regions leaves a vacuole in the centre of the cell or filament; the nucleus, where its size has permitted of detailed in- vestigation, has a structure quite similar to that of other plants and animals, and usually divides by mitosis, showing a well-marked spindle with cen- trosomes and asters. The development of the spindle is extranuclear in certain Uredinales. One or more nucleoli are commonly present and are thrown out into the cytoplasm during karyokinesis. The extrusion of chro- matin bodies has been described in Helvetia crispa. The cell wall consists of cellulose; often a special variety known as fungus cellulose is present. The storage materials include amylo-dextrin or soluble starch, amyloid, a reserve-cellulose, both of which turn blue with iodine; oil, glycogen, and various protein substances. The protoplasm gives rise also to a number of ferments which not only enable the plant to deal with its food materials, but bring into solution the walls of the host cells, and so make possible the penetration of parasitic hyphae. Sexual reproduction among the fungi takes place by the union of two uninucleate or multinucleate cells which may be similar in structure and behaviour, or may be differentiated as an antheridium and an oogonium. Each of these organs contains one or more distinct gametes, or else a number of gametes which do not become rounded off from one another or separated from the wall of the parent cell, but are indicated by separate nuclei lying in an undifferentiated mass of cytoplasm. To organs of the latter type the term coenogamete is sometimes applied in recognition oftheir multinucleate character; it is, however, inappropriate, since they are not gametes, but gametangia. In the vast majority of fungi free swimming gametes are not developed; the sole exceptions are found in the genus Monoblepharis, where uniciliate or biciliate spermatozoids are set free and swim to the female organ. A state of affairs in which the antheridium as a whole must grow or be carried to the oogonium involves a risk that normal fusion will fail to occur, while at the same time the presence of multinucleate sexual organs and of vegetative cells between which anastomoses readily occur offers considerable opportunities for some form of "reduced" fertilization. The replacement of normal fertilization by the fusion of two female or two vegetative nuclei, or i] GENERAL CHARACTERS OF THE FUNGI 3 of a female and a vegetative nucleus, is very common among fungi, and a complete disappearance of even this reminiscence of a sexual process is by no means rare. It has been suggested that the variety of food material which fungi as parasites and saprophytes obtain from their substratum may make the stimulus of fertilization less important, and it is possible also that among these plants competition is less severe than among holophyta or holozoa. .\t any rate the group shows a progressive disappearance of normal sexuality. I he sexual fusion or its equivalent is followed in all investigated cases by a reducing division or meiotic phase, so that, as in other plants or animals, the number of chromosomes is doubled in fertilization and sub- sequently halved in meiosis, and diploid1 and haploid phases follow one another. The meiotic phase is usually associated with spore-formation which, in many of the lower fungi, takes place on the germination of the zygote. In a much greater number of cases a period of vegetative development inter- venes between the association of the nuclei in fertilization or otherwise and chromosome reduction, and we have a well-marked alternation of generations in which a haploid gametophyte bears the sexual cells or their equivalent, and a diploid sporophyte gives rise to spores which in turn constitute the first stage of a new gametophytic generation. It is not at all uncommon to find several sporophytes arisingfrom a single gametophyte, and the gametophytic mycelium frequently sends out branches which grow around and protect the sexual cells and their products. Where fertilization or any equivalent process has wholly disappeared we may expect to find a similar morphological alternation of generations, though without the corresponding cytological changes; but in some cases, as in the large group of Fungi imperfecta a sporophyte is no longer developed, or at any rate has not been identified. Spores and Spore mother-cells. In the higher fungi the characteristic spores of the sporophyte, with the development of which meiosis is definitely associated, may be produced either cndogenoiisly as ascopores in a mother- cell of definitely restricted size termed an ascus, or exogenously as basidio- spores on the exterior of a cell or row of cells known as a basidium. The asci or basidia are frequently arranged in parallel series forming a fertile layer or hymenium sometimes of considerable extent. They arise from a sub-hymenial layer immediately below the hymenium, and among them are interpolated elongated vegetativecells or paraphyses, which are probably concerned in their nutrition and perhaps assist spore dispersal by keeping the mother-cells separate. The ascus and basidium and their products have long been recognized as essential features in classification. 1 The diploid unit may be defined as a protoplast the nuclear content of which includes the double number of chromosomes. 4 INTRODUCTION [ch. In the lower fungi, spore formation may be associated with the meiotic phase, but the spores produced resemble those concerned in the accessory methods of reproduction. Accessory spores. The accessory or non-sexual methods of repro- duction have no relation to any sexual process either normal or reduced, and therefore no significance in the alternation of generations; they are devices for rapid multiplication comparable with the gemmae in Marchantia or the arrangements for vegetative propagation in higher plants. The spores concerned may be borne either on the sporophyte (rusts, etc.) or, as in the majority of cases, on the gametophyte. In many of the lower fungi zoospores are developed in spherical, ovoid or tubular zoosporangia ; this is the case especially in aquatic forms. In relation to the change from aquatic to subaerial conditions the contents of the sporangium may come to be shed as walled non-motile spores, or the sporangium may itself be set free without division of its contents. Such a structure, borne externally on its parent hypha, is termed a conidium, and is the characteristic accessory reproductive unit of the fungi. In the large majority of cases the conidium germinates by means of a germ-tube, but where the fungus has not completely abandoned its aquatic habit the conidium, if it falls in wet conditions, may give rise to zoospores either in- ternally or in a vesicle borne on a short hypha. The conidia are developed either singly or in groups on conidiophores; these may be free, they may be gathered into a sheaf or coremium, or they may be formed inside a special flask-shaped receptacle known as a pyenidium ; they show an almost endless variety in form and arrangement. A less common reproductive cell is the chlamydospore; these are borne either singly or in chains in the course of the ordinary vegetative hyphae or at the ends of special branches; they are characterized, as their name im- plies, by an exceptionally thick wall. In certain species and under certain conditions whole hyphae may break up into series of separate cylindrical cells or spores. Such a spore is termed an oidium. Oidium-formation appears to be a rapid and efficient method of multiplication and is the only one found in the fungi of such diseases as favus (Ac/torion Schoenleinii), pityriasis versicolor (Microsporon furfur) and thrush (Monilia albicans). In these cases attempts to cultivate any more characteristic fructification have failed, and the fungus cannot therefore be assigned to any particular group. Morphology of the spore. The individual spore whether belonging to the principal or accessory fructification is, when first formed, a hyaline, colourless cell ; in the course of development it may divide to produce a row or a mass of cells and in the latter case is described as muriform ; >l (iKXKRAL CHARACTKRS OK TIIK KUNG1 5 it may also become variously coloured. In the large majority of cases the spore is enclosed by a double wall consisting of a delicate endospore and an epispore which may be smooth or variously sculptured; it may develop small projections and is then said to be waited or verrucose, or it may be reticulate, exhibiting a number of more or less regular polygonal depressions between which anastomosing ridges are present. Man_\- conidia and other thin walled fungal spores possess the power, in suitable media, of budding or sprouting; giving rise, that is to say, to new cells as simple lateral outgrowths which are soon nipped off. This method of propagation is shown in the conidia of the yeasts, in some of which it has wholly superseded the development of a mycelium. Asco- spores are found to bud in the Exoascaceae, and basidiospores in the Ustilaginales. Classification. The fungi are divided into three great groups according to the septation of their mycelium, and the characters of their principal spores. KUNGI vegetative mycelium aseptate l'lIVCOMYCETES characteristic spores endogenous, ascospores I ASCOMVCETES vegetative mycelium septate characteristic spores exogenous, basidiospores I BASIDIOMYCETI-'.S They may be further subdivided as follows: PHYCOMYCETES mycelium rudimentary or obsolete Archimycetes sexual reproduction by oospores ; asexual spores often motile ( him i .'. i. Saprolegniales 2. Peronosporales mycelium well developed sexual reproduction by zygospores ; asexual spores non-motile Zygomycetes i. Mucorales 2. Entomophthorales INTRODUCTION ASCOMYCETES [CH. 1 ascocarp, if present, 1 . ascocarp wide open 1 ascocarp flask-shaped ; either with no definite when ripe ; asci in opening by an ostiole ostiole, or shield-shaped, parallel rows when ripe ; asci in or with asci irregularly parallel rows arranged 1 Plectomycetes Discomyceles Pyrenomycctcs i. Plectascales 1. Pezizales I. Hypocreales 2. Erysiphales 2. Helvellales 2. Dothideales 3. Exoascales 3. Phacidiales 3. Sphaeriales 4. Hvsteriales 4. Laboulbeniales 5. Tu berales number of basidiospores indefinite H emibasidiomycetes I. Ustilaginales BASIDIOMYCETES number of basidiospores definite, usually four basidium septate Protobasidiomycetes 1. Uredinales 2. Auriculariales v Tremellales basidium continuous A utobasidiomycetes 1. Hymenomycetes 2. Gasteromycetes SAPROPHYTISM, PARASITISM AND SYMBIOSIS Since fungi under no circumstances possess chlorophyll, they are neces- sarily dependent for their food supply upon some sort of relation with another organism. As saprophytes they may utilize organic storage materials (sugar, etc.) or waste products, or may break up dead tissues as a source of supply; as parasites they may prey upon living cells with consequences to the host that vary from trifling inconvenience to complete destruction, or as symbionts they may establish a relationship with another organism in which the advantages are not wholly on one side. These various arrangements are connected by intermediate forms, and by forms capable of parasitism or saprophytism according to circumstances. A species which is strictly limited to one type of nutrition is an obligate saprophyte, parasite, or symbiont, a species which is usually saprophytic but capable of parasitic existence on occasion, is described as a hemi- saprophyte or facultative parasite, and a form which is usually parasitic, but sometimes saprophytic as a hemi-parasite, or facultative saprophyte. i] SAPROPHYTISM 7 SAPRQPH1 TISM According to our present knowledge the large majority of fungi are saprophytic; a considerable proportion of forms in each of the great groups and especially a very large number of the Basidiomycetes obtain their nutrition in this way. On Wood. Ascomycctes and Basidiomycetes arc important agents in the breaking up of wood; their hyphae absorb the starch and protoplasm of the unaltered cells of the wood and medullary rays and penetrate into the fibres, vessels and tracheids, either passing through the pits and especially the bordered pits, or penetrating the walls. They act upon the walls so that these become delignified and give characteristic cellulose reactions and the middle lamella is dissolved. The enzyme responsible for this change was first isolated by Czapek in the case of Merulius lacrymans, the fungus of dry rot. Its action seems to spread in a plane parallel to the surface of the wall either from the pits, which thus become much enlarged, or from the delicate passages left by the protoplasmic connections which originally traversed the walls of the young wood elements. The whole mass of wood loses weight and may reach the easily broken and almost powdery condition known as touch-wood. In this way considerable damage may be done to timbers (dry rot, Merulius lacrymans), paving blocks (Leutiuus Icpidctts), etc., but also considerable advantage may ensue from the restoration to the soil of the material of fallen tree trunks, twigs and branches. The part played by the higher fungi is here specially important as almost the only other agents of destruction of lignified tissues seem to be certain molluscs and Crustacea which act by boring into the wood. On Soil. Yeasts and filamentous fungi arc abundant in woodland soils and they are also of frequent occurrence in cultivated soil; the microscopic forms show a remarkable similarity in different localities; even in Europe and America the same genera and often the same species are obtained ; in culture there is a regular succession of forms, first the Mucoraceae, then Penicilliant and Eurotium and later the black and brown Hyphomycetes. A large number of Basidiomycetes also develop in the soil. The fungi of the soil utilize the sugar, starch, pectose and hcmi-cellulose which are returned to the ground in dead plants and plant org ins, and, in common with certain bacteria, they act upon cellulose, breaking it up into soluble substances and humus. In several cases evidence has been brought forward that some of these fungi are capable of assimilating free nitrogen but negative results have also been very common. The activity of these fungi is well exemplified by the "fairy-rings" of dark green grass often seen in poor pastures. The soil just outside the ring is rich in the mycelium of one or two common fungi; few hyphae are found 8 INTRODUCTION [ch. under the ring itself and none in the area enclosed by it. The ring is depen- dent upon the growth of the fungus which spreads outwards in all directions from the centre, the mycelium dying off as the food materials in the soil are exhausted; in the transition region, where the fungal hyphae themselves are disintegrating, the soil is in high condition, it contains organicresidues recently formed and capable of rapid change and the grass is especially luxuriant; the ring accordingly is just inside the region of maximum fungal activity. A certain number of fungi belonging to theTuberales, Elaphomycetaceae, Terfeziaceae and Hymenogasteraceae are completely subterranean or hypogeal in their development. They produce closed fructifications pro- tected by a stout wall of interwoven hyphae. As the spores approach maturity the fructifications develop a strong scent, varying much in character and from the human standpoint either pleasant or disagreeable, which serves to attract animals and especially rodents. The fructification is eaten and the spores pass uninjured through the alimentary canal, and are thus dis- tributed. The truffles {Tuber spp.) are the best known of these forms. Coprophilous Fungi. Fungi feeding on organic remains in the soil often benefit by the presence of natural manures and incidentally help to break up these substances so that they become available for the higher plants. From such fungi it is no great transition to the extensive coprophilous flora of which the habitat is the dung of various animals and especially of herbivorous species. In addition to the rich nitrogenous food supply which these fungi obtain, the presence of cellulose in the straw and other vegetable debris in the dung is an important factor in their nutrition. This is well shown by the fact that many coprophilous species fail to fruit in artificial culture of dung decoction and agar, unless they are provided with cellulose. Cotton wool or pieces of filter paper laid on the substratum admirably serve this purpose; the latter are soon broken into small flocculent scraps. In nature Zygomycetes, Ascomycetes and Basidiomycetes succeed each other in fairly regular order and, speaking generally, show very similar adaptations to their habitat. In man}- Ascomycetes (Ascobolaceae, Sordariaceae) the spores are surrounded by mucilage and form together a projectile which owing to its weight can be shot to a much greater distance than would be possible for single spores. The sudden ejection of the spore mass seems to depend on the absorption of water by the mucilaginous contents of the ascus. After ejection the mass dries up and becomes firmly attached to the substratum on which it has fallen. In the same way the spores in the sporangium of Pilobolus are surrounded by a gelatinous envelope which swells in the presence of water and bursts the sporangium wall, so that the whole sporangium is shot off as a single mass and adheres by means of the gelatinous layer to the body against which it strikes. The grass surrounding the dung receives an ample supply of spores and i] SAPROPHYTISM 9 spore masses; later, if it is eaten by some herbivorous animal, the spores pass uninjured through the alimentary canal and germinate while still in the intestine or on being ejected with the dung. In some cases the wall of the spore seems to have become so effectually adapted to resist injury during its passage through the animal that it is incapable of either stretching or cracking as a preliminary to germination except after digestion or some other special treatment. Thus de Bary succeeded in germinating spores of species Pilobolus and Minor in water and those of Sordaria and Coprinus in nutrient solution, by exposing them to a temperature between 35 and 40° C; Massee and Salmon obtained germination in the spores of Ascobolus perplexans, and A. glaber, after about 20 hours in either tap water or dung decoction, at a temperature of about 27°C; I found that spores of Lachnea stercorea germinated in an alka- line medium (preferably dung decoction) after incubation for several hours at 38° C. (the temperature of the body of the cow), and Welsford succeeded by the same means in germinating the spores of Ascobolus furfuraceus, and Cutting those of Ascophanus carneus. Ramlow, however, describes the ger- mination of spores of the last named species at room temperature in twenty- four hours. Further, Dodge was able to germinate the spores of several Ascobolaceae on dung agar by exposing them for 5 or 10 minutes to a temperature of 50° to 70° C, and Ramlow germinated those of Ascobolus immerstts by sowing them on agar which was still hot after sterilization. In certain cases the action of direct sunlight was found by Dodge sufficient to induce a moderate percentage of germinations and to raise the temperature of the liquid containing the spores to about 500 C. in half an hour. finally, as I am informed by Mr Ramsbottom, germination may be in- duced mechanically by cracking or breaking the epispore, for example by rubbing the spores between two coverslips, so that all the above methods are a mere variety of means towards this end. In the case of Lachnea stercorea, spores incubated for 18 to 40 hours, either in a succession of digestive fluids, or in dung extract, only germinated appri iximately 50 hours after the beginning of the experiment. It is probable that they do so in nature about two days after being swallowed. In Asco- phamis carneus, also common on cow dung, germination is much more rapid, taking place under similar circumstances in a single night, so that the spores under natural conditions may be inferred to germinate while actually in the intestine. Further development, however, is in all cases dependent upon the fungus reaching the exterior of the mass of dung. In Coprinus sterquilinus, Baden found that not only warmth and an alka- line medium (aqueous extract of horse dung), but the presence of certain bacteria also was necessary for germination. Appropriate bacteria may sometimes be a factor in the development of the ascocarp (Molliard) and io INTRODUCTION [ch. there are many indications that certain fungi grow better in impure than in pure cultures. This, however, may merely indicate that in a mixed culture the waste products of one organism are used up by the others, whereas in a pure culture they tend to accumulate and inhibit growth. Thus Dodge found that spores of Ascobolus Winteri failed to germinate on the agar in which the parent ascocarps were growing. I n the case of Mucor and R/iizopus, Baden found that the presence of bacteria prevented the germination of the spores. It may be worth con- sidering whether the progressive development of bacteria in the dung may be a factor in the succession of fungi which appear on it. Another factor of some importance in the development of coprophilous and perhaps of other fungi is the action of direct sunlight. Cultures which remain sterile in a darkened room can often be induced to fruit by placing them in a sunny window; reference has already been made to the occasional action of sunlight on spores. Many coprophilous fungi are moreover posi- tively heliotropic; this is well shown by the sporangiophores of Pilobolus and the perithecia of Sordaria and its allies. The ejection of the spores into an open space is in this way ensured. Fungi on Fatty Substrata. It is probable that all or most fungi are able to utilize fats and oils; such substances are a common form of food reserve in the spores (zoospores, oospores, uredospores, etc.), in the mycelium, and especially in the sclerotia where, in the case of Claviceps purpurea, the proportion of fat reaches as much as 35 per cent.; in several cases the fat- splitting enzyme, lipase, has been extracted. It is therefore not surprising that man}' fungi grow readily on a fatty substratum, some, such as Empusa and species of Cordyceps, on animal re- mains, some on other fungi and some on oil-containing fruits and seeds and on cotton, rape and other oil-cakes which are made from the waste re- maining after such seeds have been crushed ; they may reduce the oil content of the cake from over 10 per cent, to between 1 and 2 per cent, in two years. Eurotium and Penicillium occur on the layerof sweet oil placed over bottled fruits to prevent decomposition and together with other genera are concerned in the "ripening" of cheese. The related J\fonascus heterosporus does con- siderable damage in parts of Australia and New Zealand if it is allowed to get a footing on stored tallow. Fungi producing alcoholic Fermentation. A number of fungi obtain nutriment from solutions consisting largely of soluble carbohydrates and they may also obtain energy by directly breaking up certain of these sub- stances without the intervention of oxygen and with the formation of ethyl alcohol, carbon dioxide and small quantities of other substances. This reaction is due to the presence of the enzyme zymase and is known as alcoholic fermentation. i] SAPROPHYTISM M In its simplest possible form it may be represented by the equation : C,HiaO,= 2C!H,0 + 2COJ Only certain monosaccharides with the formula C„H1S06 (glucose, fructose) are capable of undergoing alcoholic fermentation; polysaccharides (cane- sugar, lactose, maltose) must undergo a preliminary hydrolysis resulting in the production of appropriate monosaccharides before alcoholic fermentation can take place. The majority of the fungi capable of inducing these changes are yeasts (Saccharomycetaceae) acting either alone or in conjunction with appropriate bacteria; they are very commonly present as epiphytes on the skin of ripe fruits and feed on the drops of sugary solution that ma)- be exuded or escape where the skin is broken. At other times, even in the winter, the)- may be found in the neighbouring soil, but they are very rarely present upon unripe fruits, presumably because any cells that happen to be carried there soon die. .\ number of yeasts are made use of economically in baking, where their value depends on the formation of carbon dioxide, causing the dough to "rise," as well as in brewing and the other processes concerned with the production of alcohol. The characteristic yeast of wine which ferments glucose (or grape- sugar)is found in abundance at vintage time on the grapes and their stalks, and the cider yeasts on apples ; the yeast of beer on the other hand, which acts on the sugar formed in germinating barley, is not known in the wild state. In the production of a number of alcoholic beverages the yeast acts sym- biotically with one or more bacteria ; this is the case in the group of organisms included in the "ginger-beer plant"1 which, added to commercial ginger, sugar and water, causes the formation of ginger-beer. The "plant" has the appearance of lumpy irregular masses rather like pieces of soaked tapioca or sago; its essential constituents, as Marshall Ward demonstrated in 1892, are the yeast Saccharomyccs pyrcformis and the bacterium B. vermiforme; the bacterium is able to utilize the products of the metabolism of the yeast, and can do so most successfully at their first formation, that is, in the neighbourhood of the living yeast cell; the yeast benefits by the removal of these substances, the accumulation of which would inhibit its development, and is able, in the presence of the bacterium (and of appropriate food materials), to continue its activity for weeks as shown by the evolution of carbon dioxide. The relation between the two organisms is thus a symbiosis in which each constituent gains by its association with the other. A similar combination appears to exist in the materials used for two different fermentations of lactose or milksugar which underlie the productions of the beverages known as kephir and koumiss. Kephir is prepared from 1 The ginger-beer plant is al i i as Californian bees and by other popular names ; both lately ami after the Crimean War a tradition arose that it had been brought to this country by soldiers from overseas. Cf. J. Ramsbottom, Trans. Brit. Myc. Soc. 1920, p. 86. 12 INTRODUCTION [CH. cows' milk in the Caucasus, and koumiss from mares' milk in South Western Siberia. In both these cases the formation of alcohol depends on the yeast, and that of lactic acid is due to bacterial activity. A different type of association is found in the preparation of the Japanese rice wine or sake. Here the starch of the rice is hydrolysed by Eurotium Oryzae and the resultant sugar is fermented by a yeast. In other cases zymase is secreted by filamentous fungi such as Rhizopus nigricans, Penicillium glaucum, and Eurotium nigrum. Mucor racemosus and certain other species when cultivated in sugar solution form ovoid cells which multiply by budding and cause active fermentation. Soot Fungi. The soot fungi (Meliola, Capnodium, etc.), like the wild yeasts, are epiphytic saprophytes; they occur on leaves frequented by green fly and obtain their food from the " honey-dew " excreted by these insects. Their mycelium grows rapidly and forms a sooty coating on the leaves of the host, but does not become thick enough to injure them by excluding light. SAPROPHYTISM: BIBLIOGRAPHY 1892 Ward, H. MARSHALL. The Ginger-Beer Plant and the Organisms composing it. Phil. Trans, clxxxiii, p. 125. 1895 KLOCKER, A. and SCHIONNING, H. Experimentelle Untersuchungen iiber die vermeintliche Umbildung des Aspergillus oryzae in einem Saccharomyceten. Centralbl. fiir Bakt. Abt. ii; i, p. 777. 1896 KLOCKER, A. and SCHIONNING, H. Experimentelle Untersuchungen iiber die vermeintliche Umbildung verschiedenen Schimmelpilze in Saccharomyceten. Cen- tralbl. fiir Bakt. Abt. ii; ii, p. 185. 1897 Ward, H. Marshall. On the Biology of Stereum hirsutum. Phil. Trans, clxxxix, p. 123. 1898 Ward, H. Marshall. Penicillium as a Wood-destroying Fungus. Ann. Bot. xii, p. 565. 1899 BlFFEN, R. H. A Fat-destroying Fungus. Ann. Bot. xiii, p. 363. 1899 Czapek, F. Zur Biologie der holzbewohnenden Pilze. Ber. deut. bot. Ges. xvii, p. 166. 1901 BlFFEN, R. H. On the Biology of Bulgaria polymorphs., Wett. Ann. Bot. xv, p. 1 19. 1901 Green, J. REYNOLDS. The Soluble Ferments and Fermentation. Cambridge Univ. Press. 1901 Massee, G. and SALMON, E. S. Researches on Coprophilous Fungi. Ann. Bot. xv, P- 313- 1902 VON SCHRENK, H. Decay of Timber and the Means of Preventing it. U.S. Uept. of Agr. Bureau of Plant Industry. Bull. 14, New York. 1903 MOLLIARD, M. Sur une Condition qui favorise la Production des PeYitheces chez les Ascobolus. Bull. Soc. Myc. Fr. xix, p. 150. 1905 BULLER, A. H. R. The Destruction of Wooden Paving Blocks by the Fungus Le?ttinus lepideus, Fr. Journ. Econ. Biol, i, p. 1. 1906 BULLER, A. H. R. Polyporus squamosus as a Timber destroying Fungus. Journ. Econ. Biol, i, p. 101. 1907 Fraser, H. C. I. On the Sexuality and Development of the Ascocarp in Lachnea stercorea, Pers. Ann. Bot. xxi, p. 349. 1907 Welsford, E. J. Fertilization in Ascobolus furfuraceus. New Phyt. vi, p. 136. I] PARASITISM 13 1909 Bui LER, A. 11. K. Researches on Fungi. Longmans, Green & Co., London. 1909 BULLER, A. H. R. The Destruction of Wood by Fungi. Sci. Prog, xi, p. 1. 1909 CUTTING, E. M. On the Sexuality and Development of the Ascocarp in Ascophanus carneus. Ann. Hot. xxiii, p. 399. 1912 DALE, E. On the Fungi of the Soil. Ann. Myc. x, p. 452. 1912 Dodge, B. i I. Methods of Culture and the Morphology of the Archicarp in Certain Species of the Ascobolaceae. Bull. Torrey Bot. Club, xwix, p. 139. 1913 GODDARD, H. N. Can Fungi living in Agricultural Soil Assimilate free Nitrogen? I '.mi. Gaz. Ki, p. 249. 1913 M'Ht.TH, I. ("..and SCALES, F. M. Destruction 0fCell11l1.se In l',.i, teria and Fungi. U.S. Dept. of Agr. Bureau of Plant Industry. Bull. 266, New York. 1914 Ramlow.G. Beitrage zur Entwicklungsgeschichte der Ascoboleen. Myc. Centralbl. v, P. 537- 1915 Baden, M. L. Observations on the Germination of the Spores of Coprinus ster- quilinus, Fr. Ann. Bot. xxix, p. 135. 1915 SCALES, F. M. Some Filamentous Fungi tested for Cellulose destroying Power. Bot. Gaz. lx, p. 149. 1920 HALL, A. D. The Soil. John Murray, London, 3rd ed. (Fairy Kings, p. 278). Parasitism Facultative Parasites. Several fungi which are capable of passing through their whole development as saprophytes are also occasionally found on living plants as facultative parasites or hemi-saprophytes. It was first shown by de Bary that such fungi possess the power of disintegrating and killing the tissues in advance, so that they are not parasitic in any strict sense, but first kill the cells of their host and then live saprophytically upon the dead remains. This is well seen in Botrytis cinerea, the detailed knowledge of which is due to Blackmail and Welsford, and to Brown. When the spores of Botrytis cinerea are placed in a drop of nutrient fluid on the leaves of the broad bean {Vicia faba), they show the first signs of a germ-tube in 2-3 hours; the outer walls of the developing tube soon become modified to form a mucilaginous sheath by means of which the hypha adheres to its substratum. After growing for a while along the surface of the leaf the germ-tube turns down and its tip, filled with dense protoplasm, becomes pressed against the cuticle where it may or may not swell somewhat and become spread out to form an enlargement or simple adpressorium: as growth continues the germ-tube is held firmly in place by its mucilaginous coat and the cuticle is ruptured mechanically by the pressure of its tip. The fungus now penetrates directly into an epidermal cell, or grows more or less horizontally in the subcuticular layers; in either case these layers become swollen, and in doing so appear to stretch the cuticle and make its penetration by other germ-tubes easier. As the hyphae make their way through the epidermis the cells of the palisade parenchyma become affected ; their nuclei begin to disintegrate, the chloroplasts swell, and the starch almost disappears, In the bean a dark coloration is one of the characteristic signs of death, and H INTRODUCTION [ch. this colour change spreads through the mesophyll in advance of the fungal hyphae. The hyphae, in fact, have been shown to secrete an enzyme which both disintegrates the walls of the host cells and causes the death of the protoplasts; it is however quite unable to affect the cuticle, the penetration of the outer walls of the epidermis being mechanical; a corresponding mechanism has been demonstrated in Colletotrichtim Lindemuthianum and it may be inferred that the same occurs in other less fully investigated cases. Penetration of the cuticle is, however, by no means a necessary preliminary to parasitism, whether obligate or facultative, for the hyphae of many fungi enter the host through the stomata, and in others, the so-called wound parasites, infection only takes place where a previous injury has exposed the internal tissues. It is a curious point, and one deserving further investigation, that while the germ-tubes from certain fungal spores always make use of the stomata as a means of entrance, certain others completely ignore them, even though the germinating spore happens to lie close to a stoma; it is possible that in the former case a hydrotropic or negatively phototropic stimulus and in the latter a contact stimulus alone or in addition is operative. In Botrytis cinerea hyphae sometimes grow into an already seriously infected leaf by way of the stomata: this may be related to the fact that the stomatal space becomes charged with fluid due to the breaking down of the host cells. A positively chemotropic reaction has often been suggested (Miyoshi) as explaining the entrance of the germ-tube into the leaf, but recent in- vestigation (Fulton, Robinson, Graves) show that positively chemotropic sensitiveness is weak or absent in all the hyphae studied. In Botrytis the mycelium commonly enters the cells of the host, but in other fungi it may develop wholly in the intercellular spaces, killing those cells with which it comes in contact and benefiting by the food materials that diffuse out through the dead protoplast; such forms may be described as saprophytic in the same sense as Botrytis. As might be expected fungi whose attack is mainly directed to the elements of the wood flourish equally well on living and on dead tissue; the harm that they do to their host largely depends on the fact that they cut off the water supply to the regions beyond the infected area. This is the case with Nectria cinnabarina, and the fact that in this species the ascocarps are produced on dead tissue emphasizes its saprophytic or hemi-saprophytic character. We have here a case where the survival of the host is of no ad- vantage to the attacking fungus. Obligate Parasites. In the case of obligate parasitism, on the other hand, it is evident that the death of the host involves the death of the fungus, and it is to the interest of the parasite that death should be postponed, at least until the latter has itself made provision for reproduction. i| PARASITISM 15 The relations of the parasitic fungus to its host are extremely various; some,especiallycertain unicellular parasites (<9^/<#«w, Woronina)go through tlieir whole development inside the cells of the host, some live wholly in the intercellular spaces (Gnomonia) or under the cuticle (Exoascus, Taphrind) and obtain nutriment by osmosis; others possess an intercellular mycelium from which short branches are sent into the living cells of the host; these branches may become specialized to form haustoria of limited growth and more or less definite form (Cystcpus, Ustilago, etc.). In all the above cases the parasite is inside the host and may be described as endophytic. In a certain number of forms the development of the parasite is external, and may be described as epiphytic. This is the case in many mildews (Erysiphaceae) which obtain their food supply by sending haustoria into the epidermal cells of the host; it is also the case in the Laboulbeniales where food is absorbed in many species through the unbroken membranes of the host, and where the parasite probably causes a minimum of damage and inconvenience. The influence on the parasite of its method of life is already shown at a very early stage in development. Thus the conidia or zoosporangia of Cystopus camiidus germinate better at low temperatures than high; their minimum is near zero, their maximum about 250 C. and their most favourable temperature, under ordinary circumstances, io°C. The spread of the fungus by zoospores depends on the presence of water on the foliage of the host, a fall of temperature leads to the deposition of dew, thus providing the con- dition for the activity of the zoospores, and at the same time serves as a stimulus to their development. In contrast to the above the uredospores of Puccinia dispersa, which give rise to a germ-tube directly, germinate between IO and 270 C. but most readily at about 20° C. ; the high temperatures appropriate to the germina- tion of the spores of coprophilous fungi may also be recalled in this connection. The relation between the parasite and its host may be strictly localized, as in the Laboulbeniales and in those Archimycetes which enter a single cell and complete their development within it; or the parasite may spread far beyond the point of infection, extending through or over the existing parts of the host and keeping pace with its growth when the new tissues are developed; in this way the mycelium of certain of the Ustilaginales is found \ ear after year in the tissues of the herbaceous host, dying down when it prepares for the winter, and growing with its growth; perennial mycelia are not uncommon in Hxoascaceae.Uredinales and other forms which infect trees. The parasite may modify the host tissues by its invasion, chiefly in the direction of abnormal growth < >r hypertrophy. The simplest instance of such an effect is the enlargement of a single cell due to the entrance oi the para- site; this is found in the infection of various algae and fungi by Olpidiitm, i6 INTRODUCTION [ch. and of the dandelion and other angiosperms by Synckytrium ; in the latter instance the cells surrounding the seat of infection are also enlarged. In many cases fresh cell formation as well as enlargement of the host cells takes place; this may be limited to the neighbourhood of the infected spot so that the host organ becomes locally deformed ; thus " peach leaf curl " and many similar abnormalities are formed by Exoascus and its allies; and irregular rose-coloured blisters are produced on the leaves of Ericaceae in- fected by Exobasidium. More elaborate deformations are produced by some of the Ustilaginales, and, in the case of "witches'-brooms," by the rusts and Exoascaceae. A witch's-broom is a bunch of modified twigs, caused usually by insects, but sometimes by fungi. In the latter case it is the product of a lateral bud, which, stimulated by the presence of the fungus, or by the food material which the cells of the fungus deflect from its proper course, grows out to form an abnormally dense bush of twigs; its leaves are produced earlier than those of healthy branches and, even in the case of normally evergreen conifers, are deciduous, falling off at the end of each season. Here the specialized shoot, in spite of its contained parasite, appears to flourish, though to the detriment of the rest of the tree; it may indeed be suggested that something approaching symbiosis has been established, but in this relationship the fungus is clearly the dominant partner1. Symbiosis The physiological conditions under which the thallus of a lichen is built up are somewhat similar; the algal cells appear healthy and are capable of vegetative multiplication, but the fact that the fungus alone is concerned in the development of the fructification sufficiently indicates its supremacy. In the case of Therntutis orlutina the alga is devoured by the fungus in preparation for the formation of the fruit. In mycorhiza, that is in the structures formed by the association be- tween the mycelium of a fungus and the roots (or other organs) of one of the higher plants, the advantages of the symbiotic relation often belong less to the fungus than to its partner so that the vascular plant may actually become dependent on its fungal associate and unable to develop in its absence. The mycelium may be either endotrophic, forming a skein of branched and interwoven filaments in the cells of the host and sending comparatively few hyphae to the exterior; or it may be exotrophic, that is to say mainly ex- ternal in development. Endotrophic Mycorhiza. An extreme case of obligate symbiosis has been described by Rayner for the ling, Calluna vulgaris, which grows in association with a fungus resembling the members of the genus Phoma in 1 For bibliography, see p. 19. I] SYMBIOSIS 17 its morphological characters. The mycelium not only extends through the roots and colourless parts, hut grows into the subaerial tissues ol the stem, leaves, flowers and fruit. Moreover the seedling is regularly infected 011 germination hy the hyphae which have penetrated the seed coat. When deprived of its fungus by sterilization of the seed, the seedling fails to develop, its root system in particular being inhibited; when subsequently infected from artificial culture it renews its growth. If, however, a weak seedling is inoculated from a vigorous culture it is completely parasitized and destroyed; the fungus in such a case may be regarded as having escaped from the con- trol of its partner. The fungi present in the orchids investigated by Bernard were referred to the form genus Rhfcoctoiiia1, certain species of which have been shown to be conidial stages of the basidiomycete Hypochnus. It is significant that conidia are never produced on a healthy host plant, though they can be obtained when the mycelium is grown in culture; in the cells of the host a tangled weft of hyphae develops and ultimately undergoes digestion, forming an amorphous mass. In Odontoglossum the mycelium does not enter the stem, and in Vanda and its allies it is confined to the perennial roots; in the Cattleyeae the roots are deciduous and their disappearance is followed by an autonomous phase; in B let ilia hyaeinthina, also, the mycelium never invades the green, superficial rhizome, but the young roots are regularly in- fected as they reach the length of a few centimetres. In winter the orchid is represented by its rhizome alone and its activity at the beginning of fresh growth is consequently autonomous; the symbiotic phase follows on the development of the new roots and lasts about six months, covering the period of the maturation of the seeds. During the autonomous phase the fungus vege- tates in the soil and loses, to some extent, its "virulence" or power of infection. Bletilla differs from the cases previously described in that its symbiosis is facultative and development can take place without infection, but the seed- lings grow slowlyand aredelicate; inoculation bya mycelium greatly reduced in virulence has little effect, the hyphae enter a few cells and are at once digested ; a mycelium, on the other hand, which has attained a high degree of virulence, penetrates at once to the region of attachment of the suspensor and instead of undergoing premature digestion spreads through the host cells while the seedling grows rapidly and its lower part swells to form a protocorm. The restriction of the mycelium to the non-chlorophyllous regions of these orchids is not accidental, for the contents of certain of the stem cells have a pi iisi mi mseffecton thefungus. It follows that here the mycelium cannot penetrate into the ovary and the infection of the germinating seed is conse- quently a matter of chance, hence the difficulty frequently experienced in inducing the germination of orchids. ' Burgefl, in iyoy, proposed the new generic name Orcheomyces for these fungi. G.-V. 2 18 INTRODUCTION [CH. Kusano has shown that the rootless, saprophytic orchid, Gastrodea elata, becomes dependent on the formation of mycorhiza only on the incidence of its flowering period ; it is capable of vegetative growth without infection, and the distribution of the fungus in its tissues is strictly limited; the fungus in this case is Armillaria mellea, a well-known facultative parasite. This may be regarded as a relatively early stage in the development of endotrophic symbiosis in which the angiosperm succeeds in utilizing as a factor in its own nutrition the mycelium of the attacking parasite. It suggests that in this relationship we are dealing not with an association of two or- ganisms for the benefit of both, but with a struggle between the would-be parasite and the host which controls, makes use of, and finally becomes dependent upon it. The balance of power is often very delicate, and any weakening on the part of the angiosperm gives the fungus an opportunity to assume the parasitic habit ; thus the endotrophic fungus regularly becomes parasitic on the old stamens and corolla of Arbutus and on the dying leaves. Endotrophic mycorhiza occurs in the Ericaceae and in their allies showing, so far as investigation has gone, the same extreme conditions as in Calluna; in certain Gentianaceae, Solanaceae, Labiatae, Umbelliferae, Ranunculaceae and Liliaceae, in most if not all orchids, in species of Viola and Arum, and, according to the researches of von Tubeuf, in gymnospermous trees other than the Abietineae. Endotrophic mycorhiza is also found in certain liverworts and mosses, and in many of the Pteridophyta. It is well developed in the prothallus of Lycopodium and in the leafy plant of species of both Lycopodium and Selagiuella, in the roots of Cyathea and of several of the Marattiaceae, and in both the prothallus and sporophyte of the Psilotaceae and Ophioglos- saceae. In most of these cases it does not appear to be essential to the nutrition of the sporophyte since the latter seldom shows a correlated reduc- tion of the assimilatory apparatus, but it is often a principal factor in the nutrition of the prothallus, which in the presence of mycorhiza may be subterranean and lacking in chlorophyll. Mycorhiza has been recorded in a number of fossil plants. Bernard has suggested a relationship between tuberization and the presence of an endotrophic mycelium. It is significant that very many sym- biotic plants, including notably the orchids and the sporophyte and gameto- phyte of the lycopods, tend to assume a tuberous habit or to develop bulbs or protocorms. Bernard's researches have disclosed mycorhiza in tuber- forming species of Solanum, indicating a similar origin for the potato. Exotrophic Mycorhiza. The majority of our forest trees, including Abietineae, Salicaceae, Fagaceae and Betulaceae, as well as some other plants, possess an exotrophic mycelium forming a dense felt over the apical parts of the infected roots; under this influence the development of root hairs is i] SYMBIOSIS 19 impeded and characteristic short, coral-like branches are formed. Sar codes sanguinea and Monotropa Hypopitys are non-green holosaprophytes with exotrophic mycorhiza; in the former the whole root system is covered by the mycelium of the fungus, in the latter the apices alone are free. In other cases infection seldom takes place in all roots; it is extensive in soils rich in vegetable debris, and is absent in poor soils free from humus; under these circumstances root hairs are formed and the roots function in the normal way. When present it would appear that the mycorhiza not only absorbs water anil dissolved salts, but the vascular plant is further enabled by its means to utilize directly the organic remains in the soil. The relation between an exotrophic fungus and its host, at least when the latter contains chlorophyll, would appear to be much more casual than is the case with endotrophic forms; like the latter it may arise as an at- tempted parasitism on the part of the fungus, controlled and utilized by the vascular plant. The absence of exotrophic mycorhiza in poor soils may depend at least as much on the absence of saprophytic mycelia capable of causing infection, as on the fact that a fungal associate would, under the circumstances, be of little value to the green plant. Exotrophism would seem to be more to the advantage of the fungal partner than endotrophism, since fructifica- tions are often found on mycelia in exotrophic association with the roots of vascular plants; and some subterranean species, such as the truffles, fruit only in the neighbourhood of appropriate trees. The fungi concerned in these curious relationships include representatives of all the great groups; the endotrophic mycelium of the prothalli of Lyco- podium has been referred to the genus Pytkium, and that of the Marattiaceae to Stigeosporium, a genus nearly related to Pliytoplithora, that of several orchids to Rhiaoctonia (= Hypoc/inusl) and of others to Nectria; the myce- lium of species of Elaphomyces forms mycorhiza with the roots of Pinus and other conifers; that of the Boleti with conifers and grasses and with willow, poplar, Ik irnbeam and birch, that of Tricholouia terreum with beeches and firs, that of Lactarius piperatus and of species of Cortinarius with beeches and oaks, that of species of Geaster with conifers. Reference has already been made to the association of Armillaria mellea with the orchid Gastrodea elata, and of Pkoma-WVc species with the Ericaceae. finally there is little doubt that several of the Tuberaceae and Hymeno- gasteraceae are frequent constituents of mycorhiza. PARASITISM AND SYMBIOSIS: BIBLIOGRAPHY 1863 de Barv, A. Recherches sur le deVeloppement de quel<|ucs champignons parasites. Ann. Sci. Nat. xx, p. 95. 1888 Ward, H. Marshall. Some Recent Publications bearing on the Sources of Nitrogen in Plants. Ann. Hot. i, p. 325. 1890 ill iver, V. W. On Sarcodes sangvinea, Torr. Ann. Hot. iv, p. 303. 2—2 20 INTRODUCTION [ch. 1891 FRANK, B. Ueber die auf Verdauung von Pilzen abzielende Symbiose der mit endotrophen Mycorhizen begabten Pflanzen, so wie der Leguminosen und Ellen. Ber. d. deutsch. Bot. Ges. ix, p. 244. 1894 Miyoshi, M. Ueber Chemotropismus der Pilze. Bot. Zeit. lii, p. i. 1902 Lang, W. H. On the Prothalli of Ophioglossum pendulum and Helminthostackys zeylanica. Ann. Bot. xvi, pp. 28 and 36. 1904 Cavers, F. On the Structure and Biology of Fegatella conica. Ann. Bot. xviii, p. 95 1904 Ma.SSEE, G. On the Origin of Parasitism in Fungi. Phil. Trans. B. cxcvii, p. 7. 1904 Weiss, F. E. A Mycorhiza from the Lower Coal Measures. Ann. Bot. xviii, p. 255. 1905 Gallaud, I. Etudes sur les mycorhizes endotrophes. Rev. Gen. Bot. xvii, p. 1. 1906 FULTON, H. R. Chemotropism of Fungi. Bot. Gaz. xli, p. 81. 1908 Bower, F. O. The Origin of a Land Flora. Macmillan & Co., London, pp. 240, 477 ct seq. 1909 Bernard, N. L'eVolution dans la symbiose des Orchide'es et leurs champignons commensaux. Ann Sci. Nat. 9me ser. ix, p. 1. 1909 Burgeff H. Die Wurzelpilze der Orchideen. Fischer, Jena. 191 1 Bernard, N. Sur la fonction fungicide des bulbes d'Ophrydees. Ann. Sci. X.it. 9n'e six. xiv, p. 221. 191 1 Bernard, N. Les mycorhizes des Solatium. Ann. Sci. Nat. gm" sen xiv, p. 235. 191 1 Kusano, S. Gastrodea elata and its Symbiotic Association with Armillaria mel/ea. Journ. Coll. Agric. Tokio, iv, p. 1. 191 1 Melhus, 1. E. Experiments on Spore Germination and Infection in Certain Species of Oomycetes. Univ. Wise. Agric. Expt. Sta. Research Bull, xv, p. 25. 1914 Kohinson, W. Some Experiments on the Effect of External Stimuli on the Sporidia of Puccinia malvacearum Mont.). Ann. Bot. xxviii, p. 331. 191 5 RAYNER, M. C. Obligate Symbiosis in Calluna. Ann. Bot. xxix, p. 97. 1915 BROWN, W. Studies in the Physiology of Parasitism. I. Ann. Bot. xxix, p. 313. 1916 Blackman, V. H. and Welsford, E. J. Studies in the Physiology of Parasitism. II. Ann. Bot. xxx, p. 389. 1916 BROWN, W. Studies in the Physiology of Parasitism. III. Ann. Bot. xxx, p. 399. 1916 Graves, A. H. Chemotropism in Rhizopus nigricans. Bot. Gaz. lxii, p. 337. 1916 RAYNER, M. C. Recent Developments in the Study of Endotrophic Mycorhiza. New Phyt. xv, p. 161. 1917 Brown, W. On the Physiology of Parasitism. New Phyt. xvi, p. 109. 1917 DufrenoY', J. The Endotrophic Mycorhiza of Ericaceae. New Phyt. xvi, p. 222. 1917 West, C. On Stigeosporium Marattiacearum and the Mycorrhiza of the Marattia- ceae. Ann. Bot. xxxi, p. 77. 1919 Dey, P. K. Studies in the Physiology of Parasitism. V. Infection by Colletotrichitm Undemuthianum. Ann. Bot. xxxiii, p. 305. 1921 RAMSBOTTOM, J. Orchid Mycorhiza. Catalogue of J. Charles worth & Co., Haywards Heath, p. 1. SPECIALIZATION OF SAPROPHYTISM AND PARASITISM Fungi vary very much in the extent to which they are adapted or re- stricted to a particular habitat. In some species the range is very wide, as in the case of Eurotium herbariorum or Penicillium glauaim which may occur under suitable conditions of temperature and moisture on almost any plant remains, on plant products such as bread or jam, or on substances of animal origin and, in the case of Penicillium, especially on cheese. Eurotium herbariorum and some other species are even found in the human i] SPECIALIZATION 21 ear, where they produce the condition known as otomycosis aspergillana, but they develop on the secretions and not in the living cells, so that, although they give rise to a disease, they are not true parasites. Similarly Synehyti ium aureuni infects all sorts of dicotyledons and Phyl- lactinia Corylea occurs on the leaves of many trees. In other cases the range is s. imewhat narrowed ; many species of Hydnutk are found only in fir woods, Pyronema confluens and a number of other fungi occur in nature only on burnt ground, Onygena equina is restricted to the hoofs and horns of various animals, and several species (Sordaria macrospora, Podospora coprophila, Ascobolus immersus, Ascopluznus equinus, etc.) develop upon different kinds of dung but on no other substratum. Some of the coprophilous fungi on the other hand may appear in addition on other sub- stances, especially on those rich in cellulose — Ascophauus carneus has been recorded upon paper or rope, Gymnoascus Reesii on wasps' nests, Xylaria Tulasnei on soil. Parasites again may be limited to hosts of a particular family; Cystopus candidus to the Cruciferae, Claviceps purpurea to grasses, Ustilago violacea to the Caryophyllaceae. Still greater restriction is observed in the case of such saprophytes as Erinella apala on the dead stems of species of J uncus and Pi/acre faginea on rotten beech wood, and in the case of the parasites which attack the species of a single genus, such as Rhytisma Acerinum on Acer, Polystigma rubrum on Primus, Peronospora Euphorbide on Euphorbia. Even more definite is the specialization of fungi which are capable of obtaining nutriment only from a single species; this occasionally happens among saprophytes, such as Dasyscypha dandestina on dry stems of Rubus idaeus; it may be surmised that in many such cases new habitats will ulti- mately be brought to light. Among parasites restriction to a single species is very common ; Sclerotifiia tuberosa forms its sclerotium attached to the rhizome of Anemone nemorosa, I: 1 'asms lU/ulac develops on Betula alba, and Ustilago Maydis on Zea Mays. De Bary gave to this state the name monoxeny, in contradistinction to the term polyxeny, which he applied to cases where hosts of several different species may be attacked. Every sort of intermediate grade ma}- exist between those outlined above; parasites may attack only two or three closely related members of a genus {Exobasidium Rhododendri on Rhododendron hirsutuni and R. ferrugineum), they may attack a genus and one or two species belonging to related genera, the}- may be capable of development on certain genera of a family and not on the rest, or again, while commonly restricted to a particular family, they may occur also on members of neighbouring groups; thus Phytophthora infestans is found usually on the Solanaceae and exceptionally on the scrophulariaceous species Anthocerds viscosa and Schi :aulhus Grahatni. 22 INTRODUCTION [ch. In all the cases of parasitism considered above, the fungus, whether monoxenous or polyxenous, is capable of passing through its whole existence on a single host. A different type of specialization appears in those fungi which require two host species for the completion of their life-history, and produce characteristic spores on each. Such forms are said tobe heteroecious in contradistinction to the autoecious species on a single host. Heteroecism. Heteroecious species may be either monoxenous or poly- xenous, that is to say they may be limited in relation to either or both their stages to a single species of host, or they may be capable of occurring on a number of different forms. Heteroecism is known in Sclerotinia Ledi but in no other fungi except the Uredinales or rusts, and its full consideration must be postponed till that group has been described. It may be considered here as one of the possible alternatives confronting a parasite on a host which dies down early in the year. Under such circumstances the parasite may continue its development on the dead tissue, it may await in the form of resting spores the reappearance of its host, or its spores may prove capable of germinating on a new host species, and it may carry on its development as a parasite and reinfect its original host next spring, thus becoming heteroecious. It must be noticed, however, that by no means all the existing spring or summer hosts of heteroecious fungi die down early in the year, so that other and possibly secondary factors will have to be considered. Biological species. There is no doubt that within wide or narrow limits related host plants are apt to show common susceptibility to infection ; this is well exemplified by Puccinia Malvacearum which was first observed in this country on cultivated hollyhocks in 1873 and has since established itself on the indigenous species of Malva, Altliea and Lavatera as well as in green- houses on Abut Hon. Common susceptibility may even be used as a criterion of relationship, so that liability to the attacks of Piptoceplialis Freseniana, the obligate parasite of the Mucorales, has afforded a means of distinguishing new members of that group. These facts point to a definite adaptation on the part of the fungus to its habitat; this adaptation may be very simple, a species, for example, would not be likely to occur on dung unless its spores could pass uninjured through the alimentary canal of an animal, or it may reach the complexity of a delicately balanced reaction between host and fungus, as in some of the mycorhiza described in the preceding pages. Specialization has been most fully investigated and has possibly reached its highest levels in the adaptation of various rusts and mildews to their . graminaceous hosts, but it is shown in varying degrees by other fungi1. Like 1 Wormald has shown that there are two biological species of Monilia (Sclerotinia) cinerea, one of which produces a Blossom Wilt and Canker Disease on the apple tree while the other is unable i] SPECIALIZATION 23 many fruitful mycological discoveries this was foreshadowed by de Bary, who in [863, noticed that the structural differences between the aecidia of Chrysomyxa Rhododendri and C. Ledi were so slight that he regarded these as "rather biological than morphological species." Thirty years later Eriksson recognized that the rust of wheat, Puccinia Graminis, which infects wheat, barley, rye, oats and various wild grasses, is a collective species, consisting of a number of biological forms which, though they differ in no recognizable structural character, yet differ in the powers of infection of their spores, since uredospores grown on wheat are incapable of directly infecting rye, barley or oats, those on oats cannot directly infect wheat, rye or barley, and those on barley and rye, though they can infect both rye and barley, will not develop if sown on oats or wheat. Now Puccinia Graminis is a heteroecious species producing two kinds of spores (uredospores and teleutospores) on grasses, and aecidiospores in cluster-cups on the barberry. But, though all the different biological forms alike develop their cluster-cups on the barberrry, Eriksson found that they remained constitutionally distinct, for aecidiospores derived from the form upon oats proved capable of infecting among cereals only oats, aecidiospores from the form upon rye or barley, only rye or barley and so on. In other words each form of Puccinia Graminis is so closely adapted to the particular cereal on which it occurs that its spores can only attack successfully and directly that particular graminaceous host or a limited number of its immediate allies. Marshall Ward, working with the uredospores of Puccinia dispcrsa, made clear that the susceptibility or immunity of the host does not depend on structural characters, and suggested rather the existence of enzymes or toxins or both in the cells of the fungus, and of antitoxins or similar sub- stances in the cells of the host. This hypothesis has been greatly strengthened by the work of Marchal and of Salmon on the Erysiphaceae or mildews in which group both the conidia and ascospores of biological species are similarly specialized in their powers of infection. Not only are there no structural peculiarities in the resistant hosts of these fungi, but Salmon was able, by suitable treatment, to break down their resistance. This may be achieved in various ways: (1) a minute piece of tissue, including the epidermis and the greater part of the mesophyll, is cut with a razor from one side of the leaf and spores are sown on the opposite side; (2) the leaf to be inoculated is touched for a few seconds on the upper surface with a red-hot knife and the spores are sown on the lower surface opposite the burnt spot. The result of such treatment is the ready infection of host species to cause infection except of a flowerdirectly inoculated. Biological species have also been identified among smuts, and by Diedicke in Pleospora. 24 INTRODUCTION [CH. normally immune from the attacks of the biological form used. Thus if conidia ol Erysiphe Graminis growing on wheat, are sown on uninjured leaves of wheat and barley, the result is the infection of the wheat but never of the barley; yet the conidia grown on wheat readily infect the uninjured surface of a cut or burnt barley leaf; in the case of the burnt leaf, where the whole thickness of the leaf in the burnt region becomes discoloured and apparently dead, the mycelium is found on the living cells which border the altered patch. Since the cuticle, hairs and other anatomical characters of the epi- dermis on which the spores are sown are not affected by the treatment of the cut leaf, it is clear that resistance does not depend on such factors; it must be referred, as in the case of rusts, to the physiological condition of the cells or of their contents. In nature injuries caused by insects are sufficient to destroy in the same way the resistance of the potential host. These facts have a practical bearing since diseases on the weed grasses surrounding a field of corn, even if they are not able directly to affect the uninjured leaves of the crop, may establish themselves on injured tissues. The various hosts of a given morphological species of fungus differ very much in their susceptibility to infection by the different biological forms of the parasite; thus Bromus racemosus, though markedly susceptible to its own form of Erysiphe Graminis, is completely immune against infection by conidia of the same species grown on B. commutatus, B. interruptus, B. velu- tinus and others. This immunity is particularly remarkable in the case of conidium on commutatus conidium on secalinus _xv racemosus Jx_ conidium on velutinus conidium on interruptus conidium on hordeaceiis the conidia from B. commutatus, since B. racemosus is morphologically so close to B. commutatus that it is regarded by most systernatists as no more than a variety of that species. conidia on arduennensis conidia on commutatus conidia on secalinus conidia on adoensis i] SPECIALIZATION 25 Another remarkably resistant species is Bromus mollis, yet the so-called />'. " hordeaceus" the seed of which was sent to Cambridge from Petrograd, and which is morphologically indistinguishable from />'. mollis, is nevertheless susceptible to infection by the biological species which B. mollis is able to resist. In other words the morphological species />'. mollis includes two groups or races possessing distinct physiological (or constitutional) characters and respectively immune and susceptible to infection. In the case of certain parasitic fungi, and especially of Puceinia glumartim, the yellow rust on wheat, Biffen has shown that resistance to the attacks of the parasite is a recessive character in the Mendelian sense. When a variety susceptible to rust was crossed by another practically immune from it, the offspring was at least as much infected as the original rusty type. In the next generation segregration took place in the ordinary way, three-quarters of the plants being rusty and the remaining quarter standing green and un- injured among them. In relation to this investigation Marryat showed that the rust hyphae are checked after entering the stomata of the resistant plants either by the death of the host tissue locally, accompanied by the starvation and death of the parasite, or, after a more protracted struggle, by the gradual degeneration of the invading hyphae. If, as has been suggested above, resistance depends on the presence of an antitoxin, the dominance of sus- ceptibility in this case must be taken to indicate that the development of the antitoxin is inhibited by the presence of some additional factor in the dominant forms. Cases may be expected where, in the absence of an inhibitor, resistance is dominant and depends on the presence of the anti- toxin or its progenitor. Such a case is suggested by the work of Biffen on the inheritance of immunity to ergot, but here two factors appear to be involved. The susceptible races have in some instances an importance beyond that implied in their own liability to infection; it has been suggested that they may serve as a bridge by which the fungus can pass from its original host to a species resistant to direct attack. This was indicated by the work of Marshall Ward on Puceinia dispersa, and by Salmon using Bromus "hordeaceus" as a bridging host. Inoculation experiments showed that the form of Erysiphe (i rami ins < >n Bromus racemosus was incapable of developing on uninjured B. commutatus but that it never failed to produce full infection on /.'. "hordeaceus" The mycelium on its new- host gave rise in due course to conidia and some of these, when transferred to B. commutatus, succeeded in establishing themselves and produced full infection in eight days. 26 INTRODUCTION [ch. Freeman and Johnson, in 191 1, described barley as a bridging host for biological forms of Puccinia Graminis on other cereals and, in the same year, Pole Evans found that the heterozygote between strains immune and susceptible to infection by black rust was even more susceptible than the susceptible parent and was capable of acting as a bridging species from which the immune parent could be infected. On the other hand an increasing number of investigators, working with isolated strains under rigidly controlled conditions, have failed to confirm the existence of bridging species and, according to Stakman and his assistants, there is no evidence that biological species are changed by their sojourn on a particular host. Such a change would imply a certain physiological plasticity on the part of the fungus, since it would be capable of becoming acclimatized, on the bridging host, to conditions similar to those awaiting it on the form resistant to direct attack. In the case oi P actinia Graminis the problem is further complicated by the fact that a considerable number of biological forms are parasitic on the varieties of wheat, so that the same variety may be susceptible in one locality and immune in another according to the distribution of the parasite. SPECIALIZATION OF PARASITISM Etc.: BIBLIOGRAPHY 1863 de Barv, A. Recherches sur le developpement de quelques champignons parasites. Ann. Sci. Nat. ser. 4, xx, p. 5. 1894 Eriksson, J. Ueber die Specialisirung des Parasitismus bei den Getreiderostpilzen. Ber. der deut. Bot. Ges. xii, p. 292. 1898 Eriksson, J. A General Review of the Principal Results of Swedish Research into Grain Rust. Bot. Gaz. xxv, p. 26. 1902 DlEDICKE, H. Ueber den Zusammenhang zwischen Pleospora- und Helmintho- sporium-Arten. Centralbl. f. Bakt. ix, Abt. ii, p. 317. 1902 Ward, H. Marshall. On the Relations between Host and Parasite in the Bromes and their Brown Rust, Puccinia dispersa (Erikss.). Ann. Bot. xvi, p. 233. 1902 Ward, H. Marshall. Experiments on the Effect of Mineral Starvation on the Parasitism of the Uredine Fungus, Puccinia dispersa, on Species of Bromus. Proc. Roy. Soc. lxxi, p. 138. 1902-3 Marchal, E. De la Specialisation du parasitisme chez VErysiphe Graminis. Comptes Rendus, cxxxv, p. 210, and cxxxvi, p. 1280. 1903 Ward, H. Marshall. Further Observations on the Brown Rust of the Bromes, Puccinia dispersa (Erikss.) and its adaptive Parasitism. Ann. Myc. i, p. 132. 1903 Salmon, E. S. On the Specialization of Parasitism in the Er> siphaceae. Beiheftc 2, Bot. Central, xiv, p. 261. 1903 Salmon, E. S. Infection Powers of Ascospores in the Erysiphaceae. Journ. Bot. xli, pp. 159 and 204. 1904 Massee, G. On the Origin of Parasitism in Fungi. Phil. Trans. B. cxcvii, p. 7. 1904 Salmon, E. S. Cultural Experiments with Biologic Forms of the Erysiphaceae. Phil. Trans. B. cxcvii, 229, p. 107. 1904 SALMON, E. S. On Erysiphe Graminis DC. and its adaptive Parasitism within the Genus Bromus. Ann. Myc. ii, p. 255. I] REACTIONS TO STIMULI 27 1905 WARD, II. MARSHALL. Recent Researches on the Parasitism of Fungi. Ann. Bot. xi\, p. 1. 1907 Biffen, R. H. Studies in the Inheritance of Disease Resistance. I. Joum. Agr. Sci. ii, p. 109. 1907 Makkvai, I>. C. E. Notes on the Infection and Histology of two Wheats immune to the Attacks <>f Puccinia glumarum, yellow Rust. Journ. Ag. Sci. ii, p. 129. 191 1 Freeman, E m. and Johnson, K. C. The Rusts of Drains in the United States. U.S. Dept. Ag. Bureau of Plant Industry. Bull. 216. 191 1 POLE EVANS, I. B. South African Cereal Rusts, with < Miservations on the Problem of Breeding Rust-resisting Wheats. Journ. Ag. Sci. iv, p. 95. 1912 BlFFEN, R. H. Studies in the Inheritance of Disease Resistance. II. Journ. Ag. Sci. iv, p. 421. 1914 VARILOV, X. I. Immunity to Fungous Diseases as a Physiological Test in Genetics and Systematics, exemplified in Cereals. Journ. Genetics, iv, p. 4')- 1915 STAKMAN, E. C, PlEMEISEL, F. J., and L.EVINE, M. N. Plasticity of Biologic Forms of Puccinia i,'rf>ns nigricans* is negatively chemotropic to some secretion of its own mycelium and that the negative response is much 1 Rhisopus nigricans, Ehrenb.= Mucor slolonifer, Ehrenb. 28 INTRODUCTION [ch. greater than any positively chemotropic reaction towards food or oxygen. Fulton, in 1906, found for a number of different germ-tubes that they tend to turn from a region in which hyphae of the same kind are growing, to one destitute of hyphae or in which hyphae are less abundant. A very simple example of this reaction is found in the circular growth of mycelia both in nature and in artificial culture. In so far as a clear field is available, hyphae tend to grow equally in all directions from the point where infection took place. The same factor may account, as Stevens and Hall have suggested, for the alternate dense and sparse zones which characterize man}- fungal colonies and are independent of changes in light and temperature. Energetic growth results in the deposition of katabolic substances, and growth is corre- spondingly reduced till a few scattered hyphae pass beyond the inhibiting influence and give rise to a new ring of richly branched mycelium. In older colonies the germination of fresh spores outside the zone of staling substances doubtless adds to this effect. The very definite character of the reaction is demonstrated by the ex- periments of Graves, who used the germ-tubes of Rhizopus nigricans on con- trasted agar media separated by a perforated mica plate. Hyphae developing in agar made up with turnip juice grew towards the perforations which led to fresh but otherwise identical agar on the other side of the mica plate. Hyphae under similar conditions turned from turnip juice, in which growth had taken place, to plain agar, or indeed to any fresh substance that was not in itself definitely repellant, even if, as in the case of plain agar, its nutritive value was low. On the other hand, the hyphae turned away from the perforations in the mica plate if these led to nutritive agar on which mycelium had already developed and if the substratum on which the germ-tubes were growing was by comparison fresh. This was the case even after the mycelium on the staled agar had been taken away, the products of its metabolism which re- mained in the agar having themselves a repellant effect. This effect was removed by exposure to a temperature of 100° C, showing that the staling substances are altered or destroyed by heat. A somewhat different example of the inhibiting effect of these katabolic staling substances was observed by Balls for the "sore-skin" fungus of cotton. When the nutritive medium is limited in extent, growth comes to an end more rapidly at high temperatures than at low. This is due not to the earlier exhaustion of the available food supply, but to the more rapid ac- cumulation of staling substances when growth is accelerated. Media in which growth has come to an end prove capable of supporting further growth if diluted with an equal quantity of water. By this means the staling substances are sufficiently diluted to lose their inhibiting effect, while the nutritive materials, even though diluted, are still sufficient to support growth. I] REACTIONS TO STIMULI 29 By the addition of staled media to his cultures Balls was able to show that accumulation of staling substances was a limiting factor in the growth of his fungus. The products of past metabolism are not the only factors which exercise a negatively chemotropic influence; Miyoshi showed that hyphae tend to grow away from acids, alkalis, alcohol, toxic compounds and certain neutral salts. He also brought forward evidence of the positively chemotropic effect of a number of salts and of sugar and other nutritive materials; but his results are vitiated by the fact that he was unaware of the importance of staling substances and accepted, as due to the attraction of the new medium, curva- tures which really depended on the repellant effect of the old. Neverthe- less, positive chemotropism exists and may be observed when the staling substances have been taken into account. Thus Graves found that, while all the germ-tubes of Rhizopns nigricans turned from the turnip juice agar on which they had been growing to fresh turnip juice agar, only 60 to 90% turned to fresh plain agar, and, when growth had just begun in the turnip juice agar and staling was consequently less, a smaller proportion of hyphae sought the plain substratum. Positively chemotropic reactions towards cane-sugar and glucose were also demon- strated but they were relatively weak. It may be inferred that the dominant influence governing the distribution of a parasitic fungus in its host, like that governing the distribution of saprophytic forms in culture, is negative chemo- tropism excited by the products of metabolism. This inference is borne out by the observation of Robinson that the germ-tubes from the basidiospores of Pnccinia M alvacearum failed to show- any positively chemotropic curvature towards fragments of the host leaf. Hydrotropism. Positive hydrotropism is probably effective in vegetative hyphae under appropriate conditions; thus Fulton found that, when spores of various species were grown on gelatine between two perforated mica plates with a relatively moist medium on one side and a relatively dry one on the other, they grew through the perforations towards the moist rather than towards the dry medium; hyphae of Mucor Mucedo grew through per- forations in a mica plate from firm gelatine into water, but hyphae of Rhizopus nigricans, though they grew into the relatively moist gelatine near the holes, turned away from the fluid water below. Germ-tubes of Puccinia Malvacearum were found by Robinson to grow from drops of water into the surrounding moist atmosphere, but on gelatine in moist air they tended to penetrate the gelatine. It would seem that the response varies, as is indeed to be expected, with the conditions of the fungus in question, but in some of these and perhaps other tropic reactions, there is at least a suspicion of the negatively chemotropic influence of staling substani es. Negative hydrotropism has been described for the sporangiophon ol 3o INTRODUCTION [ch. the Mucoralesand, together with transpiration, has been held responsible for their divergence from one another when arising from a common point. Aerotropism and Osmotropism. These factors have not so far been shown to play any important part in the directive growth of fungi. Phototropism. A considerable number of fruit bodies are sensitive to light and by means of this reaction are able to adjust themselves in a posi- tion favourable to the distribution of their spores, the direction of light indicating the direction of open space. Among the Mucorales the sporangiophores of various species of Pilobolns, Mucor, Pliycomyces and no doubt of many other genera bend towards the light. In the genus Pilobolus the hemispherical sporangium is borne on an aseptate sporangiophore which develops a swelling or bulb just below the sporangium and another at its base. A new set of sporangia matures daily and is discharged in the morning or early afternoon. The young sporangio- phores of the species studied by Jolivette1 showed a recognizable phototropic curvature about 30 minutes after their exposure to light from a new direc- tion; growth is apical and the tips, as they grow, bend towards the source of light. Curvature is arrested during the early stages of the formation of the sporangium and is resumed again when the subsporangial bulb is beginning to form; during the later stages of development curvature takes place just below the bulb. In this way the bulb and the terminal sporangium are pointed in the direction of the light and some accuracy of aim is secured. In a series of experiments, involving some 20,000 specimens, in which light reached the culture through apertures 1 cm. in diameter, nearly 90°/0 of the sporangia hit either the aperture itself or the walls within 1 cm. on each side of it. When illuminated by two equal sources of light the sporangiophores point to either one or the other; this is obviously a useful adaptation as an intermediate aim would fail of its object. When the sources of light differed the sporangia were found to be shot off in larger numbers towards the light in which the proportion of blue rays was greater. The species1 studied by Parr also responded more readily to blue or violet than to other rays, the presentation time gradually decreasing from red to violet although the sporangiophores were responsive to light from all regions of the spectrum. Among Ascomycetes a positively phototropic response is found in the necks of the perithecia in Sordaria and many other Pyrenomycetes, and is sufficiently delicate to induce a zig-zag development of the neck if the direction of light is repeatedly changed. The asci of Ascobolus immcrsus and A. furfur aceus are also positively phototropic so that an appropriate direction is obtained for the ejection of their large spore mass. As early as 1877 Brefeld recorded sensitiveness to light in the stipe of various Coprini, and found that normal pilei failed to develop in its 1 Specific name not given. i] REACTIONS TO STIMULI 31 absence. In ( 'oprinus niveus, and ( oprinus curtus, both coprophilous species, Buller found a well-marked positively phototropic response in young fruit bodies so that they push up from between <>r beneath the irregularities of the substratum. The stipe ceases to be phototropic when the pileus begins to expand and develops instead a negatively geotropic reaction; by these means the apex of the stipe is brought out into the light and the horizontal expansion of the pileus is ensured. A similar succession of reactions takes place in the development of the sporophore of Loitinus lepidcus; the young stipe is positivel\- phototropic and in the absence of light grows straight onwards without giving rise to a pileus; in a sufficiently strong illumination the pileus soon appears and, as its development proceeds, the positively phototropic response changes to a negatively geotropic one. Amanita phal- loides and A. crenulata show, according to Streeter, a positively phototropic reaction even after the appearance of the pileus. Corresponding reactions are to be expected in other pileate species growing on irregularly shaped substrata; on the other hand Agaricus cam- pestris, growing on ground, is quite insensitive to light, negative geotropism being, under normal conditions, sufficient to secure the satisfactory adjust- ment of its parts. A negatively phototropic reaction is very much less frequent than a positive response; Robinson found, however, that germ-tubes from the basidiospores of Puccinia Malvacearum and the conidia of Botrytis sp. turn away from a unilateral source of light, while those from the aecidiospores of Puccinia Poarum and from the conidia of Peronospora parasitica and Peni- cillium glaucum are indifferent. Phototaxis. A phototactic reaction has been observed by Strasburger in the zoospores of Chytridium vorax, and by Wager in those of Polypliagus Euglenae. Both these species parasitize motile green organisms, Chytridium infecting Chlawydococais pluvialis, and Polyphagus, Euglena viridis. The host organisms react to light since they obtain their carbon supplies by photosynthesis, and the phototactic reaction of the parasite brings it into the region where the hosts are to be found. Formative Influence of Light. Irrespective of phototropic response the formative influence of light is important. Buller found that the sporophores of Polyporus squamosus, though quite irresponsive to the direction of light, fail to give rise to pilei unless illuminated. The same is true of many other Hymenomycetes, including those which, like Lentinus lepideus and the species of Coprinus mentioned above, are positively phototropic. In many •cases only a brief period of illumination during the early stages of develop- ment is essential. Similarly, light appears to stimulate the development of ascocarps in certain Ascomycetes, and cultures may remain sterile in dark- ness or very dim light. 32 INTRODUCTION [CH. On the other hand Stevens and Hall found that the pycnidia of Phyllo- slicta sp. were irregularly scattered in continuous darkness but developed in regular concentric zones when exposed to the alternation of day and night; the rudiments of the pycnidia in this case are laid down mainly during the night. Geotropism. The influence of gravity has been very inadequately studied among the lower fungi, little having been done since Sachs, in his Lectures on the Physiology of Plants in 1882, described the sporangiophores of Mucor and Phycomyces as bending up and the rooting hyphae down; he worked with filaments extending in all directions from a suspended piece of bread. Kny in 1881 reported that the mycelia of Mucor Mucedo and Rhizopus nigri- cans and also that of Eurotium repens are indifferent to gravity, and Miyoshi denied any geotropic reaction in his fungi. Dawson in 1900 found that the stromata of Poronia punctata, a copro- philous pyrenomycete, show a well-marked negatively geotropic reaction from the earliest stages of their development and the same will probably prove true of other forms with upright stromata or with stalked fructifications like the Helvellales and many Pezizales. Among the Hymenomycetes negative geotropism was first recorded by Sachs in i860, and soon after by Hofmeister in 1863. In stipitate forms the stalk is always negatively geotropic as soon as the pileus develops, though, in some of the Coprini and in Lentinus lepideus, this may be preceded, as already seen, by a phase in which light is the directive influence. Buller in 1909, and Streeter in the same year, showed that the geotropic response is of the nature of a gradual adjustment. The growing stalk swings beyond the vertical line, changes its direction and swings across it again, passing the vertical two or three times before it comes to rest. Curiously enough this method is followed in Amanita crciiu/ata, in which the stalk reaches its full development in twenty-four hours, although there is not time for a complete adjustment, and the sporophore often comes to rest beyond the vertical line. The young stipe in Amanita elongates throughout its length until more than half grown ; the zone of most rapid elongation is just below the pileus, it finally becomes narrower and narrower until growth ceases. Streeter was able to locate the perceptive region in the stipe, not in the pileus. Amanita showed a definite geotropic response when placed in a horizontal position for only one minute before being rotated on a klinostat. When stimulation lasted for a shorter period (13 or 30 seconds) no upward curvature ensued but a spiral curve was formed in the direction in which the klinostat moved. The latent period of young, vigorous specimens is about 40 minutes. In the stemless Hymenomycetes, as in the stipitate forms, the orientation of the pileus takes place in response to gravity. This may be seen on any old stump where the bracket-shaped species of Thelephora, Stereum, Polyporus i] REACTIONS TO STIMULI 33 or Pofystictus grow out as horizontal plates. 1 lassclbring found that the fruit Ixxlies of Pofystictus cinnabarinus, when rotated on a klinostat during their development, were no longer differentiated into a dorsal sterile and a ventral fertile region, but that hymenial tubes were formed over the whole surface. Alike in the Hydnaceae, Agaricaceae and Polyporaccae the trama plates nt the fertile region are positively geotropic. In stemless forms this reaction is responsible for the orientation of the hymenium; it may be particularly well seen in some of the Hydnaceae where the spines grow downward whatever the orientation of the sporophore, and it could doubtless be demonstrated also in Tremellodon among the Tremellaceae. In stipitate species it appears as a supplementary reaction coming into play if further adjustment is needed when the stipe is fully grown. The limitations of the method in the gill- bearing fungi are obvious for, if the pileus is oblique and the gills undergo much curvature, they become crowded together and interfere with spore dispersal. REACTIONS TO STIMULI: BIBLIOGRAPHY 1869 HOFMEISTER, W. Ueber die clinch die Schwerkraft bestimmten Richtungen von Pflanzentheilen. Jahrb. wiss. Bot. iii, p. 92. 1877 BREFELD, O. Ueber die Bedeutung des Lichtes fur die Entwickelung der Pilze. Sitzungsberichte der Gesellschaft Naturforschender Freunde zu Berlin, p. 127. 1878 STRASBURGER, E. Wirkung des Lichtes und der Warme auf Schwarmsporen. Jena. 1N7V vi in Sachs, J. Ueber Ausschliessung der geotropischen und hehotropischen Kriim- mungen wahrend des Wachsens. Arb. d. Bot. Inst. Wiirzburg, ii, p. 209. Or Lectures on the Physiology of Plants. Eng. Trans., 1887. Clarendon Press, Oxford, p. 700. 188 1 DE BaRY, A. Untersuchungen liber die Peronosporeen und Saprolegnieen und die Grundlagen eines natiirlichen Systems der Pilze. Beitr. zur Morph. und Phys. d. Pilze, iv, p. 85 of separate. 1881 Knv, L. Ueber den Einfluss ausserer Krafte auf Anlegung von Sprossungen thallosser Gebilde. Sitz. Bot. Ver. Brandenburg, xxiii, p. 8. 1894 MlYOSHI, M. (jber Chrmotropismus der Pilze. Bot. Zeit. Iii, p. 1. 1900 Dawson, M. On the Biology of Poronia punctata (L.). Ann. Bot. xiv, p. 245. 1902 CLARK, J. F. On the toxic properties of some copper compounds, with special reference to Bordeaux .Mixture. Bot. Gaz. xxxiii, p. 45. 1906 FULTON, H. R. Chemotropism of Fungi. Bot. Gaz. xli, p. 81. 1906 Pfeffer,W. The Physiology of Plants. Eng. Trans. Clar. Press, Oxford, iii, p. 1 S3. 1907 HaSSF.LBRING, II. Gravity as a P"orm-Stimulus in Fungi. Bot. Gaz. xhii, p. 251. 1908 BALLS, W. L. Temperature and Growth. Ann. Bot. xxii, p. 558. 1909 BULLER, A. H. R. Researches on Fungi. Longmans, Green & Co, London. 1909 Stevens, F. I., and Hall, J. G. Variations of Fungi due to Environment. Bot. 1 laz. xlviii, p. 1. 1909 Siki 1 1 1 1. s. G. Tin- Influence of Gravity on tin- Direi tion of Growth of Amanita. Bot. 1 . ■'/. xlviii, p. 414. 1914 Jolivei il. II. D. M. Studies in the Reactions of Pilobolui to Light Stimuli. Bot. Gaz. lvii, p. 89. 1914 ROBINSi in, W. Some Experiments on the Effect of External Stimuli on the Sporidia of Puccinia mnhuu ,-, uiim Mont. . Ann. Bot. xxviii, p. 331. 1914 Wager, II. Movements of Aquatic Micro-Organisms in Response to External Forces. The Naturalist, No. 68g, p. 171. 1916 Graves, A. II. Chemotropism in Rhizopus nigricans. Bot. Gaz. lxii, p. 337. 1918 Park, R. The Response of l'il<!ns to Light. Ann. Dot. xxxii, p. 177. G -v. ^ CHAPTER II ASCOMYCETES The Ascomycetes include over 15,000 species, all of which, excepting only the yeasts, possess a well-developed mycelium of richly branched and septate hyphae. The cells of the mycelium may be uninucleate, as in the Erysi- phaceae and species of Chaetomium and Sordaria, or they may contain a few or several nuclei; energetic growth and a rapid succession of nuclear divisions often cause the nuclei of multinucleate elements to be arranged in pairs. Multiplication may take place by means of conidia, oidia, or chlamydo- spores, but the characteristic method of reproduction is by ascospores or spores produced in the interior of a mother-cell or ascus. The Ascospores. In the large majority of species the ascospores are elliptical in outline, but they may be spherical or globose, as in Ascodesmis nigricans, long and narrow (filiform) as in species of Cordyceps or Claviceps, or of intermediate form. They contain a densely granular or reticulate cytoplasm in which one or more oil drops are usually present. The epispore may be smooth or variously sculptured ; in several cases it is verrucose, in others reticulate; the latter arrangement is particularly well seen in Asco- bolus furfuraceus. All ascospores are colourless when first formed; they may remain so when ripe, or may assume a variety of colours. The young spore is unicellular and uninucleate1. Before it is set free the nucleus may divide, and this division is frequently accompanied by wall- formation so that, like the asexual spore of Pcllia, the ascospore may be regarded as undergoing premature germination. Divisions may take place in three dimensions, so that the spore is muriform ( fig. 1 ), or the septa may be all in one plane so that it consists of a row of cells (fig. 2 a). The multicellular spore thus produced may break up into its constituent cells, which proceed with their development independently, or it may function as a single structure. In examining any of these characters or in measuring the size of the spore it is essential to deal with fully mature examples since the distinctive sculpturing, pigmentation, etc., may not appear till late in development. Spores which have escaped naturally from the ascus may be used with safety. 1 Lewton Brain [Ann. Bot. 1901) describes the spores of Cordyceps ophioglossoides as multi- nucleate from their first inception. I II. II] ASCOMVCKTKS The Ascus. The ascus or mother-cell of the spores is a spherical, oval, club-shaped, or almost cylindricalorgan with a narrow, more or less elongated Fig. i. Pleospora sp.\ germinating spores, x iooo. base. When moderately young it contains a single nucleus which undergoes three karyokinetic divisions giving rise to eight daughter nuclei (fig. 3). Asci of the short, stout type are full of dense cyto- plasm ; in the relatively cylindrical forms the ends are usually vacuolate, but a broad, granular belt fills the middle region and contains the nuclei. The spores are cut out by free cell-formation so that a certain amountof cytoplasm remainsoutside them, constituting the epiplasm. It becomes charged with glycogen and other food substances, and is a source of supply to Fig. 1. Spores of a. Geoglossum difforme 4-v. ,1 „ 1 ,^:.,rr o^^^oc Fr.: !>. Delitschia furfuracea Niessl; the c eve lopinir spores. ;,. ,. - ' ,, , ,. . , lor c. Rhyttsma accrtnum llV-rs.l It.; form the definitive nucleus of de Bary. He at first believed that the ascus was produced in these cases, as in Eremascits, by the fusion of two independent filaments, but he was soon able to ascertain that the young ascus arises, not by the union of twi 1 separate hyphae, but from the penultimate cell of a single recurved filament. The apex of this filament receives two nuclei which undergo a simulta- neous karyokinesis, so that four are formed. One of these lies at the tip of the hypha, and one passes back into the lower part, while the other two lie in the curved portion, and become separated from their sister nuclei by transverse walls (fig. S). The terminal cell of the hypha thus contains a single nucleus and the penultimate cell is regularly binucleate ; it grows out laterally to form the ascus, and its two nuclei fuse soon after they come together. The fusion in the ascus was the first nuclear fusion observed among Ascomycetes and its discoverer, Dangeard, accepting it as a sexual process, regarded the ascus as an egg, and the sexual apparatus described by de Ban- and his pupils as at most vestigial. It is probable that this view was influenced by his first opinion that the ascus arose from the fusion of two separate filaments, but it was not modified by his subsequent discovery of the true process. Fertilization. In the following year (1895) both de Ban's observations and those of Dangeard were confirmed by Harper, working on the common mildew Sphaerotheca ffumuli1. Harper saw the development of a uninucleate oogonium and a uninucleate antheridium. He observed the passage of the male nucleus into the oogonium and the fusion there of the sexual nuclei. After fertilization the oogonium underwent septation, giving rise to a row of cells of which the penultimate contained two nuclei, and. after these had fused, developed into the ascus (fig. 9). He thus demonstrated that in this fungus there is a normal fusion of male and female nuclei, followed by a 1 Sphaerotheca ffumuli (DC.) Bar r.= Sphaerotheca Castaguei Lev. 42 ASCOMYCETES [CH. second fusion in the ascus, and in the following year he recorded the same process in Erysiphe Polygoni. Fig. 9. Sphaerotheca Hamuli (DC.) Burr.; a. and b. antheridium and oogonium ; c. entrance of male nucleus; ) from tin- terminal cell of which a third ascus (c) has arisen, x 1250. Fig. 11. Humaria rutilans (Fr.) Sacc. ; a. asco- genous hypha showing sixteen chromosomes in each nucleus, x 1950; 6. fusion nucleus of ascus passingout of synapsis, x i^oojc. fusion nucleus of ascus showing sixteen gemini, X 19=0. observations have since been widely confirmed by a number of investi- gators, and synapsis, the second contraction and the formation of typical gemini have been seen, as well as the reduction of the chromosome number. Thus in Humaria rutilans, which the exceptionally large nuclei render a convenient subject of study, each of the fusing nuclei possesses sixteen chromosomes (fig. 1 1 a), so that the definitive nucleus has thirty-two ; after meiosis is complete sixteen can be counted in each daughter nucleus. This fungus is somewhat exceptional in that synapsis begins separately in each of the two nuclei of the young ascus before they fuse (fig. 8 b) indicating 44 ASCOMYCETES [CH. that each of them is already diploid, the product of a sexual fusion, and capable of independent meiosis. In Helvetia crispa synapsis takes place after the nuclei have fused, but the two spiremes contract in separate masses at opposite ends of the nuclear area (fig. 12)1. In other investigated species only one synaptic knot is formed. f '.1 Fig. 12. Helvdla crispa Fr.; fusion nuclei in ascus showing the contraction of the chromatin in two separate masses, x 2000 ; after Carruthers. The third Division in the Ascus. The meiotic phase is followed by a third division in which a further change in the chromosome number has been described. This was first re- corded by Maire, in 1905, in the case of Morchella esculenta, and, with certain variations in detail, in two other Discomycetes. In M. esculenta there are eight chromo- somes in the first telophase, and four in the third, and also in the subsequent nuclear division which takes place in the spore. The next case to be brought forward was Humaria rutilaiis, in 1907, and two more (Ascobolus furfuraceus and Pyronema confluens) were re- Fig. 13. Ascobolus furfur n\-us Pers.; a. early ana- corded bv Dangeard in the same phase of the first division in ascus showing 14 of . - r6 daughter chromosomes; b. metaphase of the year (tig. 1 3). It was soon alter second division showing four chromosomes; c. third SU"-o-ested (Fraser, 1908) that the division showing four ; after Dangeard. &t> halving of the chromosome num- ber which had been observed in these species constituted a second reduction phase, bearing the same relation to the fusion in the ascus that meiosis bears to the fusion of the sexual nuclei. For this reduction the term brachymeiosis 1 This arrangement may occasionally be found in Humaria rutilans, and occasionally also the two nuclei of the young ascus proceed as far as the second contraction without undergoing fusion. M t«=rt= "J ASCOMYCETES 45 was proposed. The occurrence of ;i brachymeiotic reduction has since been observed in several other fungi, and has also been in several cases denied. Chromosome Association. There are a number of fungi, of which Phyllactinia Corylea is perhaps the most fully studied, in which no change in the chromosome number takes place throughout the life-history. In Phyl- lactinia, Harper showed in 1 905 that the chromosomes remain visible in strands attached to the central body throughout the resting stages. In each of the nuclei of the developing ascus eight such strands can be clearly seen (fig. 14), and their asso- ciation in pairs can be followed, so that they appear as eight strands in the spireme stage, and as eight chromosomes on the spindle. In the smaller sexual nuclei Harper found a similar arrangement. It would thus appear that in this fungus chro- mosome association follows directly on nuclear fusion, so that the fusion of two nuclei with // univalentstrands produces not a nucleus with 211 Fig. 14. Phyllactinia Corylea (Pers.) Karst.; fusion nuclei in ,im'U> showingeight chromatin strands attached at a common point ; after Harper. strands, but one with n bivalent strands. If this is so in the oogonium the nuclei which fuse in the ascus will each possess >t bivalent chromosomes, and the definitive nucleus will show not 4// univalent chromosomes but ;/ which are quadrivalent. In the same way neither meiosis nor brachymeiosis will affect the chromosome number, but will affect only the valency of the chromosomes. This is the case in Phyllactinia, where in all stages of the three divisions in the ascus, eight chromosomes are found. It must be noted, however, that in cases where no fusion occurred in the life-history except that which immediately precedes meiosis, the chromosome number would similarly remain unchanged ; the latter interpretation has been urged as evidence that forms in which the chromosome number is unaltered throughout the life-history are therefore necessarily without a fusion in the The Theory of a Single Nuclear Fusion. The possibility that the fusion in the ascus is the only nuclear fusion in the life-history of the A 1 imycetes, and represents the postponed union of sexual nuclei which had become associated in fertilization was first mooted by Raciborski in 1895, in a letter to Professor Harper, and was published in [896. This view 46 ASCOMYCETES [ch. received a considerable impetus in 1907 and 191 2, from the work of Claussen on Pyronema confluens. According to the latter author the male nuclei enter the oogonium and pair with the female nuclei, but do not fuse with them. The sexual nuclei pass in pairs into the ascogenous hyphae (fig. 15), and eventually they or their descendants fuse in the ascus. For Claussen, there- fore, there is a single fusion (that in the ascus) and a single reduction (the meiotic)inthe life-historyof/yn?ww<7. His interpretation has been followed by Schikorra on Monascus, by Faull on Laboulbenia, and by Ramlow on Asco- bolusimmersus and Ascopliannscarneus. The last-named author figures certain "fusions" in the oogonial region of his fungi, but regards them as pathological. Claussen's hypothesisdemandsthat the attraction between the sexual nuclei, though not sufficient to cause fusion, yet holds them together in the multinucleate ascogenous hyphae and is transmitted to their descendants when nuclear division has occurred1. It is based on three chief grounds: ( 1 ) the failure to observe fusions in the oogonium or their interpretation, if found, as pathological phenomena; (2) the recognition of as many chromosomes in the third division in the ascus as in the first; (3) the observation of paired nuclei in the ascogenous hyphae. The first of these grounds has a mainly negative value; in regard to the second, further investigation is very much to be desired ; the statement of the chromosome number without figures is of little value, nor is any figure of the third division significant except that of the late anaphase; in the earlier stages chromosomes are scattered about the spindle, so that there is no criterion by which a metaphase showing eight undivided chromosomes can be distinguished with surety from an early anaphase showing two sets of 1 A comparison is sometimes instituted between the sporophyte of the Ascomycetes and that of the rusts. In the rusts, however, each pair of nuclei is enclosed in a separate cell and the hypothesis of nuclear attraction throughout the vegetative phase is accordingly not required. F'S' '5- Pyronema conjttuns; sexual apparatus and paired nuclei in the ascogenous hyphae; a. antheridium ; b. trichogyne; (".oogonium; (/.ascogenous hyphae; x 1040; after Claussen. nl ASt'i iMVCETES 47 four. Further the adhesion of chromosomes already described for Pliyllac- tinia must not be forgotten. The occurrence of paired nuclei in the ascogenous hyphae was thus the most important evidence in favour of Claussen's view until in 1916 Welsford showed that the nuclei even of gametophytic, multinucleate hyphae are habitually paired if rapid growth and division are taking place ; this is due to the fact that mitoses follow one another so rapidly that the daughter nuclei of any parti- cular division have not time to move apart, before they them- selves divide. Such paired nu- clei have often previously been figured though without attract- ing special attention ; excellent examples are to be seen in Nichols' paper on the Pyreno- mycetes1 or in Ramlow's more recent work on Ascophaiuis car- neus*. It seems hardly possible to place a different interpreta- tion on the nuclei which lie close together in the ascoge- nous hyphae. According to our present knowledge of the cytology of the Ascomycetes there are two nuclear fusions in the life- history of these plants. The Significance of the Fusion in the Ascus. If this be the case it remains to consider the significance of the fusion in the ascus. The presence of more than one nucleus in this cell, destined to be one of the largest in the life-cycle of the fungus, is hardly surprising especially in coenocytic forms. In uninucleate species it forms part, as Harper pointed out in 1905, of the quantitative adjustment frequently observed between cytoplasm and nuclear material. But this nucleo-cytoplasmic relation does not explain why fusion should take place between the nuclei concerned or why they should be regularly two in number1. It is possible that, crowded as they are in the newly constituted ascus, the nuclei merely flow together as they make ready for the prophases of division Whatever may have been the determining - Gas. 1896, sxii, pi. xv, fig. ;:. - Myc. CentralH. 1915, pi- i. fig. 12. 3 In Humaria rutilans, however, ami doubtless in other forms, young trinucleate, and quadri- nucleate asci are found. Fig. 16. Ascophanus (-aniens Pers.; germinating spores with paired nuclei in the germ-tubes, x 450 ; after Raniluw . 48 ASCOMYCETES [CH. cause of the second fusion in the ancestors of our present Ascomycetes, it is clear that in the forms now extant the existence of a second reduction must be an important factor; in this respect the organism may well be moving in a vicious circle. Pseudapogamy. The above, at any rate, seems to be the case in respect of the much more important fusion of the sexual nuclei. In Humaria granulata no antheridium is developed, and the female nuclei, as recorded by Blackman and Fraser in 1906, fuse in pairs in the oogonium before passing into the ascogenous hyphae. The same state of affairs was observed by Welsford in Ascobolus furfuraceus in 1907, and by Cutting in Ascophanus carneus and Dale in Eurotium repens in 1909; it is difficult to see how any important physiological benefit can ensue from the union of closely related nuclei developed in the same cell; the determining cause would seem to be the need of preparation for the meiotic phase already established in the life- history. In Lachnea stercorea an antheridium is present and fuses with the terminal cell of the multicellular trichogyne, but the male nuclei never reach the oogonium, and here also the female nuclei unite in pairs. In Humaria rutilans matters have gone still further; not only is the antheridium lacking but the archicarp also is not developed. Nuclear fusion, sometimes preceded by the migration of one of the fusing nuclei, takes place in the vegetative cells of the developing apothecium. The cells containing fusion nuclei give rise to ascogenous hyphae, while those in which fusion has not occurred produce the paraphyses and the sheath. A similar state of affairs has been reported by Carruthers in Helvetia crispa, and evidence of its occur- rence in Polystigma rubrum has been noted by Blackman and Welsford. These reduced forms, belonging respectively to de Bary's categories of parthenogenesis and apogamy, have thus proved to be pseudapogamous in the sense of Farmer and Digby1, since in them normal fertilization is re- placed by the union in pairs of female or vegetative nuclei. Meiosis takes place as usual. Spore-Formation. After the third division in the ascus, preparations for spore-formation begin. This stage was first described in detail by Harper in 1895, and was subsequently elucidated by him in other papers, and especially in his very full study of the mildews in 1905. As the third mitosis comes to an end the eight daughter nuclei, or those of them about which spore-formation is to take place, become pear-shaped, a beak being pushed or pulled out from each; the centrosome lies at the tip of the beak, and from it spread the astral rays, to the activity of which Harper is inclined to attri- bute the formation of the beak. As development proceeds, these rays become folded over so that they extend past the nucleus, and Harper describes them as combining side by side to form a continuous, broad, umbrella-like mem- 1 Ann. Bot. 1907, xxi, p. 191. «] ASCOMYCKTKS 49 brane which gradually closes in to produce, by further marginal growth, the ellipsoidal plasma membrane of the spore. In this way the whole body of the spore is cut out from the undifferentiated cytoplasm of the ascus by a process of free cell formation, and its membrane is formed by the fusion of the astral rays. ,\ different account of the development of the membrane was given by Faull in 1905. According to his investigations the spore is cut out by the gradual differentiation from the centrosome downwards of a limiting layer of hyaline or finely granular cytoplasm, in the production of which the astral radiations play no part. In many of the Discomycetcs, however, the importance of the aster in spore-formation is very marked, and the spore is outlined by radiations passing out from the centrosome (fig. 17). These radiations, in Hwmaria Fig. 17. Humaria rutilans (Fr.) Sacc. ; stages of spore formation, X1875. rutilans, Peziza vesiculosa, or Lachnea stercorea, doubtless indicate the paths of altered substances emanating from the centrosome as a centre of activity, and flowing back past the nucleus as the developing beak pushes into the cytoplasm. As these substances increase a membrane is formed, and the spore, or the part of it near the centrosome, is cut out. In the delimitation of the region remote from the centrosome the vacuoles in the cytoplasm of the ascus may take part. These vacuoles are especially plentiful in Ascobolus furfuraceus, and in this fungus their share in spore-formation is important. After the spore is delimited the differentiation of its wall is largely due to the epiplasm, and is not complete till the ascus is almost ripe. Phylogeny. The recognition of the specialized character of the ascus has led to a general assumption of the monophyletic origin of the Ascomy- cetes, and speculation as to their possible ancestry has run along two main lines. They have been regarded as derived eitherfroma phycomycetous group, or from the Red Algae or the ancestors of the latter. An independent origin either anmng the flagellates or the Green Algae has also been proposed. The suggestion of a floridean relationship was first made by Sachs, in 1874, and has recently been supported by Harper, Dodge1 and others; the ; Bull, Torrey Bo/. Club, 1914, x 1 i , p, [57. G.-V. 50 ASCOMYCETES [ch. comparison of the sporogenous filaments of a Red Alga with the ascogenous hyphae, of the algal trichogyne with the unicellular trichogynes of some Ascomycetes, and of the spermatia in the two groups is certainly suggestive, but it assumes that the trichogyne in the two cases is homologous, a very doubtful point, and it involves the corollary that all the simpler Ascomycetes are derived by reduction from the more complex. The derivation of the group from the Phycomycetes was upheld by Winter in 1874, by de Bary in and after 1 881, by Brefeld in 1889, and lately by Atkinson1 in 19 14. Any conclusion however, as to either the origin or the inter-relationships of the Ascomycetes, must await a detailed knowledge of the development of the ascocarp and of the morphology of the sexual apparatus in a much larger number of species. So far the development of the ascocarp throws little light on the problems of phylogeny; in the great majority of cases the ascogenous hyphae are enclosed when young by a weft of gametophytic filaments, and, in the simplest of such cases, this arrangement persists till the asci are ripe and the gametophytic hyphae decay. In other cases there is a considerable variation in the time and extent of the opening of the fructification, though its mature form is of two main types. In view of this fact it is clear that the Pyrenomycetes, in which the perithecium is flask-shaped, opening by an ostiole, and the Discomycetes, in which the apothecium is typically cup-shaped and wide open at maturity, are justified as form groups and this long established arrangement is not contradicted by what we know of the development of the sexual organs. The Discomycetes show three types of sexual apparatus: (1) The oval antheridium and somewhat elongated, coiled archicarp of Ascodesmis. Here the archicarp ends in a one-celled trichogyne and the unicellular oogonium becomes septate after fertilization and gives rise to a few short ascogenous hyphae-. (2) An oval antheridium, unicellular trichogyne,and more or less spherical oogonium which does not undergo septation. This type is found in Pyronema, and may be traced in Humaria granulata, and presumably in other forms where a large oval cell has been seen at the base of the developing ascocarp. It is present also in Lachnea stercorea, if the septate trichogyne of this species can be looked upon as a secondary development. It is the characteristic type of the Pezizaceae. (3) A scolecite or stout septate archicarp, the distal cells of which form a trichogyne and the proximal a stalk, while the middle region is multicellular, 1 Ann. Mis. Bot. Card. 1914, ii, p. 315. - Another simple form is Thelebolus. which shows certain suggestive analogies to Sphaeiotheca, but demands further investigation. ii] ASCOMYCETES 51 the cells communicating by means of large pits, and one{Ascobolits furfura- ceus) or more ( Ascophanus carneus, Lachnea cretea, Rhizina undulatd) of them give rise to ascogenous hyphae. This is the characteristic archicarp of the Ascobolaceae and is found also in Lachnea cretea and in Rhizina undulata as well as in Collema piilposiau and some other lichens. Unfortunately the details of normal fertilization are not yet available in these forms so that it cannot be said definitely whether the oogonial region is in Lilt i- or unicellular at the fertilization stage. In many cases fertilization is known to be "reduced" and in the majority an antheridium has not been recorded. In Ascobolus carbonarius, a small, spcrmatium-like, attached cell (the male conidium of Dodge) has been observed in association with the tip of the trichogyne; somewhat similar attached cells have been seen in Collema pulposum\ in other lichens typical, detached spermatia have been described. Here the type of maximum septation is reached and shows a septate trichogyne, an oogonial region sooner or later septate, and a spermatium-like antheridium. The second or spherical type may be derived very readily from the first; the genera Ascodesntis and Pyronema are alike in the development of their sexual organs and the structure of their sheath; the significant difference between them lies in the spherical shape of the oogonium in Pyronema which may well be responsible for the absence of septation. The third or scolecitic type could also be derived through an increase of septation and reduction in the size of the antheridium from Ascodesmis; the coloured spores and reticulate epispore characteristic of that genus and of many Ascobolaceae may be, as Massee suggests, a further indication of relationship. The sexual apparatus of the Pyrenomycetes culminates in a septate trichogyne, septate oogonial region and detached antheridium (spermatium) so closely comparable with those of the discomycetous type of maximum septation as to suggest some cross relationship between the groups. The very distinct type of ascocarp, however, in Gnomonia, Polystigma and other Pyrenomycetes on the one hand, and in the Ascobolaceae and their allies on the other appears at present to negative this possibility and to indicate rather a case of parallel development. In the Laboulbeniales the trichogyne is septate, and the oogonium is unicellular and undergoes septation after the fertilization stage, but, of the row produced, only one cell gives rise to asci. The fertilizing agent may be a walled spermatium budded off externally, or it may be a non-motile mass of protoplasm ejected from an attached organ. The detailed development of the lower Pyrenomycetes has as yet been even less studied than that of the higher forms, and all that can be said is that apparently the antheridium is of a simple attached type and that the archicarp is somewhat elongated, often coiled and sooner or later septate. The larger gametangia among these forms would well repay detailed investigation. 4—2 52 ASCOMYCETES [ch. trichogyne o, oogonium i cell, never septate, antheridium attached. trichogyne o, oogonium i cell, septate after fert., antheridium attached. trichogyne i cell, oogonium i cell, septate after fert. , antheridium attached. trichogyne I cell, oogonium i cell, never septate, antheridium attached, large. PLECTOMYCETES SACCHAROMVCETACEAE ENDOMVCETACEAE I Sphaerothtca ERYSIPHACEAE (.VMXOASCACEAE en W H W u ASPERGILLACEAE L< i\\ I R PYRENO- MYCETES A nodes mis I Pyronana PEZIZACEAE CO w w u incomplete develop- ment of septate type with antheri- dium set free. > r". O 2C — LABOULBEN IALES Lachttea stercorea I Lachnea cretea Rhizina I ! ASCOBOLACEAE o u CO Collema pulposum complete development of septate type with antheridium set free. LICI EXES PYRENOMYCETES The dotted lines indicate possible and the continuous lines rather more probable relationships. ii] ASCOMYCETES 53 In the forms here grouped together as Plectomycetes, we have three or four varieties of sexual apparatus, hut the richly septate types are never reached and detached spermatia are not known. The antheridium is a uni- nucleate or coenocytic cell borne at the end of a stalk; the most elaborate archicarp is that of Eurotium with a unicellular trichogyne and an oogonium which becomes septate after the fertilization stage. In Gymnoascus there is no trichogyne and the compact sheath of the Aspergillaceae is represented by an open weft of hyphae. In the Erysiphaceae a trichogyne is not developed and the oogonium becomes septate after fertilization, but only one cell gives rise to ascogenous hyphae or (in Sphaerotheca) becomes the single ascus. In the Kndomycetaceae two enlarged cells unite, and the single ascus is the immediate product of their union. The fusing cells arise on the same mycelium as the conidia, and in Endomyces they are of different size; each is uninucleate and after the union of their nuclei the fusion nucleus divides to form the nuclei of the ascospores which may be four or eight in number; in view of "what is known in other asci it may be inferred that in the course of these divisions mciotic reduction takes place. Should this inference prove correct, and there seems no other stage of the life-history at which meiosis is likely to occur, we have here a diploid phase of the briefest possible duration, meiosis immediately succeeding fertilization. This condition may be either primitive or reduced; ascogenous hyphae have not yet been interpolated or have already disappeared. The only indication in favour of the latter hypothesis is the occurrence in certain species of three nuclear divisions in the ascus and eight ascospores; there are, however, other cases, such as the oogonium of the Fucaceae, where a third division regularly follows meiosis even when all the nuclei formed are not to be utilized, and in consequence the significance of the third mitosis cannot be pressed. If the Endomycetaceae be regarded as primitive, or rather as a simple offshoot from a primitive common ancestor, the ascogenous hyphae must be regarded as an interpolated phase in the life-history, and this interpolation seems to have entailed (i) the septation of the cell in which fertilization takes place, and (2) the formation of one or more asci from one or more of its subdivisions. These changes have been established in certain simple forms through which the rest may have been derived: 1 1 1 Erysiphaceae; the vegetative cells are generally uninucleate; the oogo- nium after fertilization divides to form a row of cells, and from one of these ascogenous hyphae gn >w out. The single ascus of Sphaerottieca and Podosphaera is presumably the result of reduction, since there seems no explanation of the development of a sporophyte unless the number of spores resulting fr< >m a single sexual act is thereby increased. As simple forms go, the sheath is 54 ASCOMYCETES [CH. n here fairly elaborate; the asci are regularly arranged. The Erysiphaceae may possibly have given rise to the Laboulbeniales, the only other group in which a single daughter cell of the oogonium is responsible for the asci, and perhaps to the lower Pyrenomycetes also; these, like the Erysiphaceae, have regularly arranged asci, and in Chaetomium fimete the perithecium is without an ostiole. (2) Gymnoasciis and its allies; thegametangiaare not much differentiated; both, like the mycelial cells, are multinucleate (it is difficult to gauge the significance of this character in Fungi) and the oogonium, or an outgrowth from it, becomes septate after fertilization and gives rise to ascogenous hyphae. Among the Endomycetaceae, Dipodascus suggests itself as the most probable representative of the ancestor of these forms. The asci in the Gymnoascaceae are irregularly arranged and the sheath is rudimentary. Clearly such a form may have given rise to the Aspergillaceae and to the rest of the higher Plectascales but perhaps to no other group. (3) Ascodesmis is a third type which might be derived either directly or through the erysiphaceous type from an endomycetous ancestor ; the antheridium and oogonium are but little differentiated, but the latter is furnished with a trichogyne and becomes septate after fertilization; the ascogenous hyphae are few and the sheath simple. Massee indeed places this genus near Gytnnoascus although the asci are regularly arranged. It cannot be far removed from the ancestor of the other Discomycetes. The table on page 52 may perhaps serve to elucidate some of these hypotheses. CHAPTHR lit PLECTOMYCETES THE group Plectomycetes is constituted to include those relatively simple forms which possess neither the cup-shaped apothecium of the Discomycetes, nor the Mask-shaped perithecium opening by a definite ostiole which characterizes the Pyrenomycetes. In the majority of the remaining Asco- mycetcs a rounded ascocarp is produced, but it opens either by the decay of its walls, or by an irregular split or tear. The asci may arise from the floor of this fructification, and stand parallel one to another, or they ma)' be irregularly disposed, the fertile hyphae forming a tangled weft. In other families the asci are naked; they stand parallel in the Exoascaceae, but in these parasitic forms their position is probably determined by the fact that the_\- grow up between the epidermal cells or under the cuticle of the host, and may be without phylogenetic significance. In the Endomycetaceae they are irregularly disposed on the mycelium, and in the Saccharomyceta- ceae a mycelium is not developed. In the majority of species the asci are club-shaped, pyriform or oval, they arise indifferently from the terminal or intercalary cells of the fertile hyphae, and the regular bending over of the tip of the ascogenous filament characteristic of the Discomycetes and Pyrenomycetes is not found among them1. The ascospores are usually continuous and hyaline; in the large majority of cases the gametophytic mycelium gives rise to conidia. In the Exoascales the asci arise on a mycelium of binucleate cells and the origin of the binucleate arrangement is unknown; but in the other main groups of Plectomycetes the form of the sexual organs has been recorded, and a number of species show functional sexuality. In the Endomycetaceae and Saccharomycetaceae fusion takes place between similar or nearly similar cells, a single fusion nucleus is formed in the zygote and there gives rise to the nuclei of the ascospores. In the Erysiphaceae the mycelial cells and gametangia are uninucleate the antheridium and oogonium differ in size and after fertilization the zygote- (oogonium) undergoes septation and one of its cells either becomes the single ascus or branches and gives rise to several asci. In the Gvmnoascaceae and Aspergillaceae the cells of the mycelium and sexual branches are multinucleate, the oogonium is furnished with a 1 The group corresponds, therefore, to Dangeard' 1 es with the addition of his Game- tangiees and Choristogamete'es (Le Botanist?, 1907, p. 28). 56 PLECTOMYCETES [ch. trichogyne and the zygote (oogonium) after septation gives rise to numerous asci which arise from its several cells. In none of the Plectomycetes are the more complicated forms of sexual apparatus reached ; the trichogyne and oogonial region are never multi- cellular and the antheridium never becomes a spermatium. The structure of the reproductive branches thus bears out the inference drawn from the characters of the ascigerous stage that the species included under the Plectomycetes are simple and for the most part presumably primitive. The group is a collection of forms at a somewhat similar level of development, and may or may not prove to be a natural arrangement ; in this it resembles the Discomycetes and Pyrenomycetes. It is within this group that the vegetative sporophyte has been developed and the fusion in the ascus established, and it is probably among these forms that the explanation of the peculiarities of ascomycetous morphology is to be sought. The group Plectomycetes includes some 1200 species and may be sub- divided as follows : Asci irregularly arranged PLECTASCALES. Asci parallel Ascocarp developed ERVSIPHALES. Ascocarp lacking EXOASCALES. PLECTASCALES The Plectascales include all those Ascomycetes in which the asci are arranged irregularly, at different levels and diversely orientated. In the better developed forms the ascogenous hyphae are enclosed in a definite peridium made up of an inner nutritive and an outer protective sheath, or they are surrounded, as in Gymnoascus, merely by an open weft of hyphae. The latter arrangement suggests a connection with the Endomycetaceae, a series of simple species in which the asci are quite unprotected ; it has been shown, by the recent studies of Guilliermond and others, that these in turn lead to species in which a mycelium is seldom developed, and finally to the typical yeasts, where the endosporogenous cells are scarcely recogniz- able as asci. To these may be added a few other simple forms of uncertain relationship so that the Plectascales include the Plectascineae, the Protascineae, and some of the Hemiasci of the authors of Engler's Natiirlichen Pflanzen- familien, and contain some of the simplest members of the Ascomycetes. Among these the Saccharomycetaceae have presumably been derived by reduction from such forms as the Endomycetaceae where a mycelium is normally developed. In both groups a single fusion occurs in the life-history and immediately precedes the formation of the ascospores. It might be in] PLECTASCALES 57 possible to regard this fusion as representing the non-sexual fusion intheascus which characterizes the members of other groups of Ascomycetes, and to look upon the gametophyte and sexual organs as having wholly disappeared. On the other hand, the fact that fusion is between separate cells, and not between nuclei located in the same cell, and the further fact that the fusing cells sometimes differ in size and behaviour (and not infrequently fail to fuse) recall characteristics of the sexual process in other fungi, and indicate that we are dealing here with forms in which the vcg. I itive hyphae are gametophytic, the uniting cells are gametangia, the diplophase is repre- sented only by the fusion nucleus, the ascospores are formed directly in the oogonium, and the anomalous second fusion does not occur. In Guillier- mondia, where the fusion cell buds out a daughter cell in which the asco- spore is produced, we may conceivably have the rudiment — or the vestige — of an ascogenous hypha, and in Dipodascus the outgrowth of the gametangium after fertilization may have a similar significance. Should the Endomyce- taceae prove to be primitive, the history of the higher Ascomycetes becomes that of the interpolation of a vegetative sporophyte between fertilization and meiosis. The Plectascales, as defined above, include the following families: Asci naked. Vegetative cells forming a mycelium ; asci distinct from vegetative cells Endomycetaceae. Vegetative cells single or loosely attached ; asci not differentiated from vegetative cells SacCHAROMYCETACEAK. Asci surrounded by loosely interwoven hyphae GYMNOASCACEAE. Asci surrounded by a definite peridium. Ascocarp subaerial Sessile Aspergillaceae. Stalked ONYGENACEAE. Ascocarp subterranean Peridium distinct from walls of ascocarp ; spore mass powdery at maturity ElaPHOMYCETACEAE. Peridium continuous with walls of asco- carp ; spore mass never powdery TERFEZIACEAE. Endomycetaceae In the Endomycetaceae the mycelium is usually well developed and bears numerous asci each of which is either the product of a separate and presumably sexual fusion, or parthenogenetically produced. Oidia, chlamy- dospores and yeast-like conidia may be formed. The majority of the Endomycetaceae are saprophytic on sugary substances or on exudations from plants. Endomyces Mali is described as an active parasite on apples and various species are parasitic on other fungi. The principal genera are Eremascus and Endomyces. 58 PLECTOMYCETES [CH. Only two species of Eremascus are known. E. albus was discovered by Eidam in 1881, in a bottle of malt extract. The contents had gone bad and their surface was covered with a growth of various fungi, amongst which was the new genus. It pro- duced a fine, snowy white, septate mycelium from which pairs of fer- tile hyphae grew out, curled round one another and fused at their tips (fig. 1 8). The fused portion was cut off from the fertile hypha below, and eventually produced eight spores. Unfortunately Eidam's species was lost and has never reappeared. In 1907, however, Stoppel, on opening some pots of apple and gooseberry jelly, discovered a very similar form which she named Ere- mascus fertilis. This species, like E. albus, possesses a branching, septate mycelium. The cells at first contain several nuclei; these, according to Stoppel, are arranged in pairs, but Guilliermond, in a subsequent investigation, found that such an arrangement, even when present in the young mycelium, did not persist. It is no doubt dependent upon rapidity of growth. From this mycelium pairs of uninucleate branches grow up, usually from the same, sometimes from different hyphae, and fuse at their apices (fig. 19). Their nuclei also fuse and after three karyokinetic divisions eight spores are formed. Sometimes, especially in old cultures, the fertile hyphae may produce asci without fusion. These are usually small and generally contain four spores or even a lesser number. As a rule three nuclear divisions take place in the parthenogenetic asci, and eight nuclei are formed, though they do not all function. According to Guilliermond it would seem that the number of spores is conditioned not by any cytological peculiarity, but rather by the supply of nutritive material. The species of the genus Endomyces possess a branched, septate myce- lium. It may break up into oidia, which sometimes become surrounded by thick walls and form cysts, or it may produce yeast-like conidia which Fig. 18. Eremasais albus Eidam; a. b. c. d. sexual apparatus; e. /. %. h. fusion of gametangia ; *'. / !;. development of asci; /. parthenogenetic ascus; x 900-1000; aft '■• Eidam. Ill PLECTASCALES 59 Fig. 19. Ereinascus fertilis Stoppel; stages in the formation of the ascus, both by fusion of two cells and parthenogenetically ; after Guilliermond. Fig. 10. Endomy , Magnusii Ludw.; a. i. antheridium and oogonium in contact; c. oogonium after fusion of sexual nuclei; d. parthenogenetic ascus; Endomyces filniligtr Lindner; e. conjugation between two neighbouring cells, al the end of the hypha is a group of young asci ; /. normal and parthenogenetic asci ; after Guilliermond. 6o PLECTOMYCETES [CH. themselves multiply by budding. Under appropriate conditions the mycelium also bears naked, four-spored asci, the development of which has been studied by Guilliermond. In Endomyces Magnnsii vegetative multiplication is by the separation of oidia cut off by transverse walls. The ascus is the product of a definite sexual process in which an elongated, swollen cell and a relatively narrow one grow up, bend towards one another and unite. The single nucleus of the smaller cell passes into the larger and fuses with its nucleus. Two karyo- kinetic divisions take place, so that four nuclei and ultimately four spores are produced (fig. 20). Fusion appears to take place indifferently between unrelated or closely related filaments and parthenogenesis is not uncommon. In E.fibuliger, about half the asci result from the union of two filaments while the remainder are parthenogenetic. The fusing hyphae are in most cases closely related, often appearing as protuberances on each side of a septum. They are similar at the time of fusion, but afterwards the growth of one ceases, while the other swells to form the ascus. Besides producing asci E. fibuliger multiplies rapidly by means of yeast-like conidia, which closely resemble the cells of species of Saccharomycos (fig. 21). Fig. 21. Endomyccs fibuligtr Lind- Fig;. 12. Dipodascus albidus Lagerh.; fusion of Con- ner; formation of conidia; after jugating cells and nuclei ; after Dangeard. Guilliermond. VVolkia decolorans, the only known species of the genus Wolkia, has a strono- mycelium, growing luxuriantly at a temperature of about 26°C; in the immature state the mycelium is light pink, later globular red bodies appear. These are the asci and are formed at the ends of single hyphae without preliminary fusion. At first they contain dense cytoplasm and a large vacuole ; later they become filled with blackish ascospores from two to fifteen in number; in old cultures the spores are sometimes septate. Ill] l'LKCTASCALES 61 W. decolorans has been identified by van der Wolk as the cause of "yellow grains," a serious disease of stored rice which is endemic in the Mast Indies and elsewhere, but is prevented by attention to thoroughly dry conditions. The only known species of Dipodascus, D. albidus, was discovered by de Lagerheim in Quinto in 1892 on the gummy secretion of Puj/a, one of the Bromeliaceae. It was found again in 1001 by Juel, in Sweden, on the sap of an injured birch, and has been described by both these investigators and by Dangeard. The mycelium consists of multinucleate cells; it may break up to form oidia and may produce many-spored asci. In the initiation of the ascus two branches grow up from the same or different hyphae and fuse at their apices (fig. 22). Both are multinucleate; one is rather larger than the other and continues its growth after fertilization to form the single ascus. Soon after the fusion of the sexual cells one of the nuclei in each is recog- nizable as larger than its neigh- bours. These two nuclei unite, usually in the larger cell, while the rest of the nuclei degenerate. The fusion nucleus passes up into the developing ascus, undergoes several divisionsand eventually gives rise to the nu- clei of the spores (fig. 23). Dipodascus differs from Eremascus and the other Endomycetaceae in the presence of accessory nuclei in its gametangia, and from all except Wclkia, in the formation of numerous spores in its ascus. In spite of these differences the resemblance seems sufficiently close to permit its inclusion in the same group. ENDOMYCETACEAE: BIBLIOGRAPHY 1883 ElDAM, E. Zur Kenntniss der Entwk kelung bui clen Ascomyceten. Cohn's Beitrage zur Biol, der Pflanzen, iii, p. 385. 1S92 dk LAGERHEIM, G. Dipodascus albidus eine neue geschlechtliche Hemiascee. Jahrb. fur. uiss. Hot. xxiv, p. 549 1902 Juel, ll. < >. Ober Zellinhalt, Befruchtung und Sporenbildung bei Dipoda Flora, xci, p. 47. 1907 Dangeard, P. A. Recherches sur lc deVeloppement du perithece chc/. les Ascomy- cetes. I.i- Botaniste, x, p. 30. 1907 STOPPEL, R. Eremascus fertilis, nov. spec. Flora, xcvii, p. 332. 1909 Guilliermond, A. Recherches cytologiques et taxonomiques sur lc Endomyce- tai 1 e K> i - 1 tin. de Bot. xxi, p. 1. Fig. 23. Dipodascus albidus Lagerh. ; development of ascus and ascospores; after Juel. 62 PLECTOMYCETES [ch. 1909 Klocker, A. Endomyces Javanensis, n. sp. C. R. des trav. du lab. de Carlsberg, vii, p. 267. 1913 VAN DER WOLK, P. C. Protascus colorans a new genus and a new species of the Protascineae Group; the source of "Yellow-Grains" in Rice. Myc. Centralbl. iii, P- 'S3- 1914 Ramsbottom, J. The Generic Name Protascus. Trans. Brit. Myc. Soc. v, p. 143. Saccharomycetaceae The Saccharomycetaceae, or yeasts, are widely distributed on, or in, all sorts of sugary media; they occur mainly as separate cells which are only exceptionally united to form a short mycelium. The individual cells are round or elliptical, bounded by a delicate membrane and containing, in the cases studied in detail, a large nuclear vacuole with a chromatin network and a well-marked, laterally placed nucleolus. Division is amitotic. In the cytoplasm are refractive granules of volutin, glycogen and oil. Multiplication is by transverse division and separation of the daughter cells (Schizosaccharomyces), or more usually by budding, that is to say by the formation of successive lateral outgrowths which ultimately assume the form and size of the parent cell (Zygosaccharomyces, Saccharomyces, Saccharo- mycopsis). Each bud receives a nucleus and cytoplasm and is cut off by a wall. Before its separation it may itself bud again, and in this way considerable colonies may be produced. Under suitable conditions, and especially when growing on a moist, solid substratum, the cell contents may round themselves up to form one to eight (usually two or four) spores. These so-called endospores are the ascospores of the yeast, the ordinary vegetative cell functioning as an ascus either independently or after conjugation with another similar cell. One of the most striking features of the yeasts and one which gives them a considerable economic importance is the power possessed by many species of producing alcoholic fermentation in certain sugars. This pro- perty is due to the presence of the enzyme zymase which is secreted by the yeast cells during fermentation, but which is not present in the resting cells, being soon decomposed when the reaction comes to an end. The activity of zymase is dependent on the presence of two co-enzymes ; the first is a soluble phosphate which enters into temporary combination with part of the carbohydrate, but it is ineffective in the absence of a second factor of unknown constitution. The unknown co-enzyme is dialysable and not destroyed by boiling; it may be separated from the yeast juice by filtration under pressure, both filtrate and residue being inactive alone. Even the yeasts which produce the largest proportion of alcohol utilize five to six per cent, of the available sugar in the formation of glycerine, Ill] l'LKCTASCALES 63 succinic acid, acetic acid, and small quantities of other substances. The amount of these by-products varies during the progress of fermentation and according to external conditions. In particular, fermentation is affei ted by the presence or absence of free oxygen. Under conditions of plentiful aeration the yeast grows and multiplies rapidly and much of the sugar is used as food; under anaerobic conditions, on the other hand, the main part of the sugar is utilized in respiration, alcoholic fermentation is more complete .unl the quantity of alcohol produced is greater in proportion to the number of cells concerned. On the ground that their daughter cells are produced by septation, and not, as in other genera, by budding, Guilliermond postulates for the species of Schizosaccharomyces a derivation from the neighbourhood of Endomyces Magnusii in which the mycelium cuts off free cells by transverse septation. lie refers such genera as Saccharomyces, in which budding occurs, to the line which gave rise to Endomyces fibuliger where asexual multiplication takes place in a similar way (fig. 24). ScM.a. L.J K Fig. 24. Diagram of the phylogeny of the Yeasts; after Guilliermond. Er. f., Eremascus ferlilis. End. I., Endomyces fibuliger. Sa. c, Saccharomycopsis capsularis. Z., Zygosaccharomyces. Sa., Saccharomyces. L. J. II, Johannesberg yeast II. End. M., Endomyces Magnusii. End. d., Endo- myces dectpiens. Sc. o., Schizosaccharomyces octos fonts. Sc. M., Schizosaccharomyces mellacei. Sc. M. a., Sch. mellacei, apogamous variety. Conjugation, as a preliminary to the formation of asci, was first described by Schionning in 1895 in Schizosaccharomyces and was afterwards studied in some cytological detail by Guilliermond (1901). In Sch. octosporus, two neighbouring cells of similar size put out processes which fuse to form a conjugation tube; the nuclei pass into the tube and undergo fusion, after which the two associated cells enlarge and form, as a rule, a single oval 64 PLECTOMYCETES [CH. Fig. 25. Schizosaccharomyces octosporus Beyrinck ; conjuga- tion and formation of ascospores ; after Guilliermond. structure, the ascus. The fusion nucleus divides to form four or eight daughter nuclei about which ascospores are organized (fig. 25). Sometimes the limits of the conjugating cells can be distinguished after the ascospores are formed, two or four lying in each of the original cells. In the closely related Sch. Pombe and Sch. incl- ined copulation takes place in a very similar way, but the union of the conjugating cells is less complete than is usually the case in Sell, octosporus, and the number of ascospores is regularly four. The mature ascus is thus dumb-bell shaped, with two spores in each enlargement. Also in 1901 Barker discovered the yeast Zygosaccharomyces Barkeri and observed in it a conjugation similar to that of Sell. Pombe. Following on these observations a number of other cases of conjugation among the yeasts have been recognized. Many species form two spores, one at each end of a dumb-bell shaped ascus; in others a single spore is produced, the fusion nucleus passing from the conjugation tube into one of the fusion cells, while the other remains empty. Such cases lead up to the state of affairs in Zygosaccharomyces Chevalieri where conjugation is between two cells of different sizes, the whole contents of the smaller passing into the larger cell which is then cut off by a wall. In the larger cell nuclear fusion takes place and one to four ascospores are formed. In Guilliermondia fulvescens conjugation is between a mature cell and its bud. The whole contents of the bud pass back into the parent cell, nuclear fusion takes place and a fresh bud is put out in which the single ascospore develops. It has been suggested that this represents a rudimentary sporo- phyte. The problems connected with meiosis hardly arise here if, as Wager has shown for Saccharomyces, amitosis is the rule. In Debaryomyces globosus, copulation takes place sometimes between two similar cells, sometimes, as in Guilliermondia, between a mature cell and its bud. In either case one or two spores are produced In most species with sexually formed asci parthenogenesis is not un- common. In Schwanniomyces occidentals and in Torulaspora Rosei it has become the rule. The cells in which the ascospores are about to be formed put out processes which are directed towards neighbouring cells at the same stage of development. But they do not fuse, and ascospores are formed in each cell independently. In T. Rosei more than one process is sometimes put out. in] PLECTASCALES 65 Such cases lead up to the conditions found in the large majority of yeasts where ascospore formation takes place not only without effective conjugation but without any vestiges of that process. Among forms with parthenogenetically produced asci Guilliermond ( 1902) has observed a peculiar process in Saccharomy codes Ludwigii. Here the rather elongated ascus gives rise to four ascospores; these on germination swell up, put out beaks towards each other and fuse in pairs. Fusion is usually between spores in the same ascus, but occasionally, when one of the four ascospores has degenerated, between spores of different groups. Each spore is uninucleate, the nuclei pass into the conjugating tube and there fuse. A similar process takes place in Willia Satumus and in the so-called Yeast of Johannesberg, II. Afterwards an outgrowth from the middle of the conjugation tube is developed ; it may give rise to a short hypha which soon breaks up into separate cells, it may produce lateral buds in an ordinary yeast-like manner, or it may give rise at once, especially on carrot and under conditions favour- able to ascus formation, to four endospores. In the last case the life-history differs from that of Zygosaccharomyces principally in the abbreviation of the vegetative phase, in other cases a vegetative phase is inserted not as usual before conjugation, but between conjugation and the development of the spores. Guilliermond regards the pairing of the ascospores as a secondarv process following the establishment of parthenogenesis. In any case it admirably illustrates the plasticity of the simpler fungi. SACCHAROMYCETACEAE : BIBLIOGRAPHY 1895 SCHIONNING, H. Nouvelle et singuliere formation de Pascus dans une levure. Meddelelser fra Carlsberg Laboratoriet. iv, p. 30. 1901 BAKK.KR, T. P. A Conjugating "Yeast." Proc. Roy. Soc. lxviii, p. 345. 1901 Guilliermond, A. Reclierches sur la sporulation des Schizosaccharomycetes. Comptes Rendus Ac. Sci. exxxiii, p. 242. 1901 HANSEN, E. C. Grundlinien zur Systematik der Saccharomyceten. Centralbl. fiir Bakt. Abt. ii; xii, p. 529. 1903 GUILLIERMOND, A. Recherches sur la germination des spores chez le Schizosac- charomyces Ludwigii. Bull. Soc. Myc. de France, xix, p. 18. 1903 LEPESi HKIN, \Y. W. Zur Kenntniss der Erblichkeit bei den einzelligen Organismen. Centr. f. Bakt. Abt ii; x, p. 145. 1905 Grii LIERMOND, A. Recherches sur la germination des spores et la conjugaison chez les levures. Rev. Gen. de Bot. xvii, p. 337. 1909 Ki.ockkr, A. Deux nouveaux Genres de la Famille des Saccharomycetes. C. R. des trav. du lab. de Carlsberg, vii, p. 273. 1910 GUILLIERMOND, A. Sur un curieux exemple de parthenoge'nese observe dans une levure. C. R. Soc. Biol, de Paris, lxviii, p. 363. 1910 GUILLIERMOND, A. Quelques remarques sur la copulation des levures. Ann. Myc vii, p. 287. G.-V. r 66 PLECTOMYCETES [CH. igio WAGER, H. and PENISTON, A. Cytological Observations on the Yeast Plant. Ann. Bot. xxiv, p. 45. 191 1 GuiLLlERMOND, A. Les Progres de la Cytologic des Champignons. Prog. Rei Bot. iv, pp. 433 and 468, et seq. 191 1 Nadson, C. A. and Konokotine, A. G. Guilliermondia, un nouveau genre de la faraille des Saccharomycetes a copulation he"terogamique. Bull, du Jard. Imp. de St Petersbourg, xi, p. 117. 1913 Marchand, H. La conjugaison des spores chez les levures. Rev. Gen. de Bot. xxv, p. 207. 1914 BAYLISS, W. M. The Nature of Enzyme Action. Monographs on Biochemistry. Longmans, Green & Co., London (and see literature cited). Gymnoascaceae The Gymnoascaceae differ from the Endomycetaceae in that their asci are borne on a sporophytic mycelium which originates from the female organ after the fertilization stage. These ascogenous hyphae are sur- rounded by a loose weft of protec- tive filaments which bear spines or variously coiled or hooked branches (fig. 26). The asci are ovoid or pyii- form, and each contains eight spores. The species of Gymnoascus occur in various habitats, on dung, bees' nests, dead grass, etc. In G. Reesii, according to Dale, two branches grow up from the same hypha, one on each side of a septum, and become twisted around one another. These are the antheridium and oogonium; their free ends swell into club-shaped heads which lie in close contact and each becomes delimited by a transverse septum. The walls between them break down, and the contents of the antheridium pass over into the oogonium (fig. 27 a, b). Both cells are at first uninucleate, but later coeno- cytic, and, though the history of the nuclei has not been traced, it seems almost certain that fusion must sooner or later occur. Up to this point the sexual cells are usually quite similar in form, but now the antheridium grows larger and more spherical, remaining almost straight, while the oogonium puts out a prolongation which winds around it, undergoes septation and soon branches to give rise to ascogenous hyphae (fig. 27 c). Fi 26. Gymnoascus sp.; a. ascocarp, x 26; b. ascus and free ascospores, x 1040. tn] PLECTASCALES 67 In G. candidus (fig. 27 d) the antheridium and oogonium already differ in form at the time of their union, and, in the majority of cases, appear to Fig. 2j. Gymnoascus Reesii Baran.; a. surface view of conjugating cells; b. the same in longitudinal section; c. a later stage, septate oogonium giving rise t" hyphae ; Gymnoascus candidus Eidam; (/. surface view of conjugating cells; e. same in longitudinal section; all after Dale. Ctenomyces serratus Eidam; /'. surface view of con- jugating cells, X400; after Eidam. arise from different hyphae. As in G. Reesii the antheridium is straight, but the oogonium elongates before fusion and grows spirally around it till the apices meet and fuse (fig. 27 e). Afterwards the oogonium undergoes septation and gives rise to ascogenous hyphae. The sheath of protective hyphae is very scanty, represented by a few thin-walled filaments. Amauroascus verrucosus forms sexual organs which, in their early stages, closely resemble those of G. Reesii. Two similar multinucleate hyphae grow up, and later one of them, the oogonium, enlarges considerably; it branches without septation, and gives rise to ascogenous hyphae which are cut off by transverse walls. Our knowledge of development in this species is due to Dangeard, who has not observed fusion between the sexual cells. In Ctenomyces serratus (fig. 27/"), which occurs saprophytically on 1 athers, organs quite similar to those of G. candidus have been described by Eidam, and more recently by Dangeard. The}- are multinucleate, and the oogonium is long and elaborately coiled and ultimately becomes seg- mented. In this species, as in the others he has studied, Dangeard regards the central hypha not as an antheridium, but as a nutritive structure which he terms a trophogone. He denies the passage of its contents into the female organ. 5—2 68 PLECTOMYCETES [CH. GYMNOASCACEAE : BIBLIOGRAPHY 1880 ElDAM, E. Beitrag zur Kenntniss der Gymnoasceen. Cohn's Beitrage, iii, p. 267. 1903 Dale, E. Observations on the Gymnoascaceae. Ann. Bot. xvii, p. 571. 1907 DANGEARD, P. Recherches sur le developpement du peVithece chez les Ascomy- cetes. Le Botaniste, x, pp. 86 and 97. A spcrgillaccae The Aspergillaceae are distinguished from the earlier families of the Plectascales by the fact that their ascogenous filaments are surrounded by a closely interwoven sheath of sterile hyphae so that a closed fruit or peri- thecium is formed. In many species, the development of an ascus-fruit is rare, and reproduction depends on the abundant and very efficient conidia; in others, which, judging by the form of their conidial fructification, should belong to this family, ascocarps are unknown. The species occur either saprophytically or parasitically upon a wide variety of substrata. Many of the saprophytic forms, including species of Eurotium and Penicillium, grow with especial readiness on fatty substances, Emericella erythrospora occurs on olives, and Monascus Iietcrosporus on glycerine or tallow. Several species. of Penicillium together with other fungi and bacteria are concerned in the "ripening" of cheese, on the proteids of which they act by means of a proteolytic enzyme. The species of Microascus, Aphdnoascus and some others are coprophilous, and several members of the family occur on wood. The parasitic forms are less numerous; various species of Penicillium and Eurotium are pathogenic on man and animals, and some, if they obtain entrance through a wound or other aperture, are the cause of ripe rot in fruit. Thielavia basicola, the only member of the family which causes an important plant disease, is sometimes separated from the Aspergillaceae and classed with the Perisporiaceae. This species infects the roots of tobacco and certain other plants, and in the early stages multiplies by means of hyaline conidia (endospores) produced inside mycelial branches, from the ends of which they are afterwards expelled, givingthe infected root a mildewed appearance. Later, thick-walled brown chlamydospores are differentiated in rows at the ends of hyaline filaments so that the root is covered with a dark coating. Normal development of the root is prevented and the host killed or stunted ; if recovery does not take place perithecia are developed on the dead plant. The formation of the perithecium in most investigated species is initiated by the appearance of sexual organs, from the stalks of which the cells of the sheath arise. In Microascus and in Emericella the sheath opens by a pore, but in the majority of cases it remains closed, and the ascospores are finally Ill l'l.KCTASCALES 69 liberated by its decay. The asci arc spherical or pyriform and contain two t< > eight continuous spores, the walls of which may be variously ornamented. In both Penicillium and Eurotium the perithecium may develop an excep- tionally thick wall, and pass into a resting stage sometimes several weeks in duration. Such a structure is described as a sclerotium. In Eurotium herbariorutn* the development of perithecia is readily induced by cultivation on prune agar- made up with forty per cent, of cane- sugar. Ripe perithecia appear after ten days or a fortnight at 15° C. A similar method should probably prove successful with other species. The only known species of Aphanoascus, A. cinnabarinus, was found by Zukal on the dung of alligators. The character of its perithecium wall ( fig. 28) suggests a transition stage between the Gymnoascaceae, in which it is Fig. 28. Aphanoascus cinnabarinus Zukal; a. elongated, septate archicarp and swollen antheridium ; />. ascogenous hyphae and sheath; after Dangeard. placed by Dangeard, and the Aspergillaceae. Multinucleate conidia are borne laterally or terminally on the mycelium. The sexual organs arise from the same or different hyphae; the antheridium (Dangeard's trophogone) becomes swollen, and the elongated archicarp, which appears at first to be without septa, coils round it;, their fusion has not been observed. Each at first contains from three to ten nuclei; later the number rises to about twenty in the antheridium and as many as fort}- in the archicarp. According to Dangeard the contents of the antheridium degenerate, though the cell itself persists for a considerable time. The archicarp undergoes septation, branches, and gives rise to asci. In the meantime vegetative hyphae grow up and invest the essential organs, forming a louse tangle around them The inner part of the investment remains in this state and is eventually absorbed, but 1 Eurotium hetbariorum (Wigg.) Link-/;'. Aspergillus glaucus till attached to a thin slice of agar. 7o PLECTOMYCETES [CH. the outer filaments form four or five parenchymatous layers which constitute a protective sheath, apparently differing but little from that of Eurotium or Penicillium. In the investigated species of the genus Eurotium {Aspergillus), the ascospores and conidia are commonly multinucleate and give rise on ger- mination to a septate mycelium each cell of which contains several nuclei. Conidiophores appear early; they arise as a rule from densely tangled knots of swollen mycelium, and appear as thick, multinucleate hyphae. The tip of the conidiophore becomes swollen and rounded off and its cytoplasm shows a reticulate arrangement. A little later numerous sterigmata bud out (fig. 29), and the nuclei stream up the strands of cytoplasm towards Fig. 29. Eurotium herbariorum (Wigg.) Link; development of conidiophores and conidia, x 6 2 ~ . them. Several nuclei pass to each sterigma and thence to the conidia which develop in acropetal succession. At maturity each conidium contains in E. repens about twelve nuclei, in E. herbariorum four, and in E. fumigatus, E.flavus and E. clavatus, as described by Dangeard, only one. The general features of the sexual organs of Eurotium herbariorum were described by de Bary in his classical researches of 1870. He distinguished a coiled, septate archicarp, and saw that its tip fused with a comparatively straight antheridial hypha, the membranes between breaking down, and he recognized that from it the asci are ultimately derived. More recently it has been shown that the archicarp of Eurotium is made up of three parts: a multicellular stalk, a unicellular oogonium, and a unicellular trichogyne. In E. herbariorum these parts may be clearly distinguished (fig. 30^), but they are not always equally definite in E. repens. Ill] PLECTASCALES In any case the archicarp becomes mure or less twisted and near it another septate hypha appears, from the end of which the unicellular antheridium is cut off. Like the cells of the vegetative mycelium, all parts of the sexual organs are coenocytic. Fusion takes place between the antheridium and trichogyne, but the contents of the male organ have not been seen to enter the oogonium. Fig. 30. Euroiium herbariorum (Wigg.) Link; <7. young archicarp; />. archicarp and abortive antheridium ; f. ascocarp containing asci and spores; x 625. Dale has observed the fusion of nuclei in pairs in the oogonium of E. repens, and Domaradsky in that of E. Fischeri, but it seems probable that we are dealing here with a union of female nuclei such as occurs in various Disco- mycetes. Even if normal fertilization sometimes takes place it is certainly not general, for the antheridium often fails to reach the trichogyne (fig. 30^), and is sometimes entirely absent. This appears to be always the case in E. flavus and it is common in other genera. Nevertheless the oogonium becomes septate and from its several parts branches develop, the nuclei pass into them, and at their ends eight-spored asci develop. The ascus is formed from the terminal or the penultimate cell of a hypha and in it a fusion of two nuclei takes place. Shortly before the septation of the oogonium, vegetative hyphae begin to grow up about the sexual organs, from the stalks of which they mostly arise as branches, and themselves branch freely. Some of the branches grow inwards forming a nutritive layer, the cells of others, as shown by de Bary, become tabular and more or less empty, they secrete a golden yellow 72 PLECTOMYCETES [CH. substance, readily soluble in alcohol, in the form of a thick, brittle pellicle. These constitute the protective sheath (fig. 30 c), by the decay of which, after the disappearance of the nutritive hyphae and later of the ascus walls, the spores are finally set free. The ascospores are spherical or lenticular often with a sculptured epispore. In most species of Penicillium reproduction takes place almost entirely by means of the abundant conidia borne in chains on the branched, brush- like conidiophores (fig. 3 1 ). Ascocarps are rare, and a detailed study of their development has yet to be made. Fig. 32. Penicillium glaucum Link; conjugating cells, X630; after Brefeld. Fig. 31. Penicillium glaucum Link; conidiophores and conidia, x 500. Brefeld, in 1871, succeeded in obtaining perithecia of P. glaucum? by cultivating his material under reduced oxygen pressure. He cautiously moistened slices of bread with distilled water, and after six or seven days, when the development of the mycelium was proceeding energetically, 1 Penicillium glaucum Link = />. crustaceum L. tn PLEC fASCALES 73 enclosed them between glass plates so as to reduce the entrance of air, and the development of conidia. Similarly Zukal a few years later obtained sclerotia by excluding air. The formation of the perithecia in Brefeld's material was initiated by the appearance of pairs of simple, stout hyphae which twisted round one another (fig. 32), and from one or both of which branches later arose. Brefeld regarded them as possibly oogonial and antheridial. A further study of these organs, the simple form of which suggests a comparison with Gymnoascus, is much to be desired. Penicillium glaucum includes several biological species or strains, and it is quite possible that Mrrlrld's success depended not only on the methods employed, but also on the use <>f a fortunate variety. Klocker, in 1903, obtained asci in his new species P. Wortmanni, and another new and very curious ascigerous species, Penicillium vermiculatutn, was described by Dangeard in 1907. The vegetative cells, unlike those of related forms, are uninucleate and bear a very scanty supply of conidia. Perithecia are abundant; in their initiation two branches take part. The oogonium is at first uninucleate but as it elongates the nucleus undergoes several divisions. In the meantime a second branch appears, usually borne on a narrower filament; it cuts off a uninu- cleate or occasionally binucleate terminal cell which applies itself to the middle of the oogonium, and the intervening walls disappear (fig. y3). Apparently, however, fertilization does not take place; the nu- cleus of the terminal cell is described as ■I' generating in situ while the oogonium undergoes septation and is transformed into a row of usually binucleate cells. Narrow vegetative hyphae grow up around this structure, and the perithecium is formed in the usual way. The archicarp of this species shows ni < importantpeculiarities but the terminal F'g- .'<:•■ Penicillium vemticulatum ,,,-.;,,, ,~1^,«.„ „ u r ..1 .1 1 1 ■ |ling-; archicarp and antheridium; uninucleate cell of the other branch is after Dangeard. 74 PLECTOMYCETES [CH. difficult to place; it seems almost inevitable to homologize it with an antheridium, but the relation of a uninucleate antheridium to a multinucleate female organ is by no means clear. Degeneration of the superfluous nuclei as in Dipodascus might be postulated. For Dangeard, the structure is a trophogone concerned only in nutrition and without sexual significance. The genus Monascus contains some five or six species, of which the most fully investigated are M. purpurcus and the form studied by Barker and since named M. Barkeri by Dangeard. This species is used by the Chinese for the manufacture of an alcoholic liquor known as Samsu. In both species there is an abundant mycelium bearing chains of ovoid conidia; later it assumes a reddish tinge and fruits are formed; their development may be traced with some readiness in hanging drop cultures. Certain branches of the mycelium cut off each a small, terminal cell which elongates and bends sideways to form the antheridium (fig. 34). A pro- longation of the penultimate cell grows up alongside it and a trichogyne Fig. 34. Monascus Barkeri Dang. ; development of oogonium, trichogyne and antheridium, X900; after Barker. and oogonium are cut off by transverse walls. The oogonium contains four to six, and the antheridium three or four nuclei. According to Dangeard the antheridial (trophogone) nuclei degenerate in situ but other authors find that fusion takes place between the antheridium and trichogyne and that the male nuclei travel through the trichogyne to the oogonium (fig. 35) where they pair with the female nuclei. According to Schikorra, nuclear fusion does not occur at this stage in M. purpureas but is postponed till the sexual Ill] PLECTASCALES 75 nuclei have travelled in pairs to the asci, where they unite; but Kuyper, in M. Barken, reports fertilization in the female organ. After the fertilization stage the oogonium enlarges and gives rise to asco- genous hyphae while the an- theridium and trichogyne de- generate. Investing filaments grow up to form a sheath, the inner layers of which consist of delicate, nutritive cells. These degenerate early, producing a mass of protoplasm amongst which the ascogenous hyphae ramify. Erom the penultimate cells of the latter binucleate asci aredeveloped, and afterthe nuclei have fused eight spores are formed. The ascus wall breaks down and the spores are finally set free after the decay of the outer layer of the sheath. This sheath, with the en- closed mass of free ascospores, was long regarded as a single organ containing an indefinite number of spores ; for this reason the fungus was placed in the Hemiasci and given the Fi< generic name of Monascus. The later stages of develop- ment are in fact difficult to follow and have been variously interpreted by different authors. Thus Dangeard describes the oogonium as undergoing septation before it branches, while Barker interprets the mass of protoplasm in which the young asci are found as the remains of the oogonium invaginated by the growth into it of the ascogenous hyphae. Kuyper and Ikeno, on similar grounds, believed the asci to be produced by free cell formation within the oogonium, no ascogenous hyphae being developed. . 35. Monascus purpureus Went.; a. b. stages in the development of the oogonium; after Dangeard. .vv .V. Schikorra ; c. entrance of male nuclei into trichogyne; d. pairing of nuclei in the oogonium; after Schikorra. ASI'ERGILLACEAE: BIBLIOGRAPHY 1870 de BARY, A. Eurotium, Erysiphe, Cincinnobolus nebst Bemerkungen iiber die Geschlechtsorgane der Ascomycetcn. Beitr. z. Morph. und l'liys. der Pilze, iii, p. r. 1874 Brefei.D, O. Botanische Untersuchungen uber Schimmelpilze, ii, Penicillium, p. 1. 76 PLECTOMYCETES [ch. 1887 ZUKAL, H. Uber Kultur der Askenfrucht von Penicillium crustaceum. K. K. zoo. bot. Gesells. in Wien, xxx, vii, p. 66. 1903 Barker, B. T. P. The Morphology and Development of the Ascus in Monascus. ■ Ann. Bot. xvii, p. 167. 1903 Ikeno, S. Uber die Sporenbildung und systematische Stellung von Monascus purpureus Went. Ber. d. deutsch. Bot. Gesells. xxi, p. 259. 1903 Klocker, A. Om Slogtem Penicilliums Plads i Systemet og Beskrivelse af en ny ascusdannende Art. C. R. des trav. du lab. de Carlsberg, vi, p. 84. 1905 Kuyper, H. P. Die Perithecienentuickelung von Monascus purpureas Went, und Monascus Barkeri Dangeard, sowie die systematische Stellung dieser Pilze. Ann. Myc. iii, p. 32. 1905 Olive, E. W. The Morphology of Monascus purpureas. Bot. Gaz. xxxix, p. 56. 1907 Dangeard, P. Recherches sur le de"veloppement du ptfrithece chez les Asco- mycetes. Le Botaniste, x, p. 118. 1907 Fraser, H. C. 1. and Chambers, H. S. The Morphology of Aspergillus herbarioru m. Ann. Myc. v, p. 419. 1908 Domaradskv, M. Zur Fruchtkorperentwickelung von Aspergillus Fischeri Wehm. Ber. d. deut. bot. Ges. xxvi A, p. 14. 1909 Dale, E. On the Morphology of Aspergillus repens de Bary. Ann. Myc. vii, p. 215. 1909 SCHIKORRA, W. Ueber die Entwickelungsgeschichte von Monascus. Zeitschr. fur Bot. i, p. 379. 1910 Tho.M, C. Cultural Studies of Species of Penici/liuiu. U.S. Dept. Agr. Bureau Animal Industry Bull. 11S. Onygenaceae The Onygenaceae include only the remarkable genus Onygena. There are some six species, all limited in habitat to such animal substances as horns, hoofs, feathers, fur and skin. This peculiarity, together with the absence of conidia, the thin wall of the perithecium, and the fact of its dehiscence by lobes or by a circular split, distinguishes the members of the group from the other Plectascales, which they resemble in the irregular arrangement of their asci. Two of the six species have sculptured spores and sessile fructifications which thus approach those of the Aspergill- aceae, while in the other four the spores are smooth and the fructification stalked. To the latter group belongs Onygena equina, described by Marshall Ward in 1899. The ascospores germinate only after a prolonged resting period or after treatment with gastric juice ; thus treated they produce a vigorous mycelium on which the ascocarp first appears as a dome-shaped mass of white hyphae ; a little later it becomes covered with loose cells among which air is entangled, rendering the fruit very difficult to wet. As development proceeds a number of hyphae grow outwards and divide into short segments, certain of which swell up and are liberated as chlamydo- spores, covering the whole of the stroma with a dense powder. Meantime the hyphae which gave rise to these become crowded together to form the pseudoparenchymatous sheath. Internally asci are produced and give rise each to eight spores, but the ascus walls soon disappear and in] PLECTASCALES 77 the spores lie free amongst the vegetative hyphae. Tin's mature stage, in which there is no trace of asci, caused Onygena to be variously classified with the Myxomycetes and with the Lycoperdaceae before its true position was discovered. There is no evidence of the existence of sexual organs. ONYGENACEAE: BIBLIOGRAPHY 1 Ward, H. Marshall. Onygena equina Willd. A Horn-destroying Fungus. Phil. Trans. B. Cxci, [>• 269. 1917 BRIERLEY, W. IS. Spore Germination in Onygena equina, Willd. Ann. Bot. xxxi, p. 17. Elaphomycetaceae and Terfeziaceae In the next two families, Elaphomycetaceae and Terfeziaceae, the fruit is subterranean. The species differ from the other hypogeal Ascomycetes, the Tuberales, with which they are still sometimes classified, and resemble the subaerial Plectascales in the irregular arrangement of their asci, which are scattered or grouped in nests surrounded by sterile branches (fig. 57). The gleba or central complex of hyphae is not at any stage of development in communication with the exterior. In the Elaphomycetaceae the ascocarp is surrounded by a thick yellow or brown peridium, the asci are subglobose and the gleba breaks up at maturity into a powdery mass of spores. The only genus is' Elaphomyces. The mycelium of certain species develops in relation to the roots of Piiuis and other conifers, and the ascocarp is often parasitized by species of the pyrenomycetous fungus Cordyceps. E. granulatus, the commonest British species, is the host of C. capitata, and E. variegatus of C. ophioglossoides (fig. 1 10). In the Terfeziaceae (figs. 36, 37) the peridium is much less distinct, and ''it;-./'- Terfezia olbiensis Tul.; section of fructification ; after Tula in Mime cases is represented merely by an ascus-free region around the periphery of the fruit. Moreover the spores do not, as in the Elaphomy- cetaceae, form a powdery mass at maturity. 78 PLECTOMYCETES [CH. Erysiphales The Erysiphales are characterized by an abundant superficial mycelium, which may be white (colourless) or dark-coloured. The perithecia are spherical, ovoid or flattened, and are usually without an ostiole; the peridium is thin and membranous; the asci are arranged in a regular layer at the base of the perithecium. The group includes some 600 species, the majority of which are external parasites or epiphytes upon the leaves of higher plants. They are grouped into three families, of which the Microthyriaceae are but little known, and of doubtful position, and the Erysiphaceae and Perisporiaceae show several points in common both with the Plectascales, from which they differ in the regular arrangement of their asci, and with the Pyre- nomvcctes, from which they are for the most part distinguished by the absence of an ostiole. Their taxonomic position is probably somewhere between these two groups, and they have, under various systems of classifi- cation, been placed in closer proxi- mity sometimes to the one and sometimes to the other. Their in- clusion here in the Plectomycetes is due to the fact that they, or rather their best-known family, the Erysiphaceae, show indica- tions of being a primitive group. The simple type of male and female organs, the latter without a trichogyne, and the simple structure of the perithecium are evidence in this direction. The families of the Erysiphales may be distinguished as follows : Aerial mycelium colourless (or white). Perithecia more or less globose without an ostiole, furnished with conspicuous appendages. Conidia of oidium type. Fig. 37. Terfezia olbiensis Tul. ; section through hymenium, showing asci irregularly arranged; after Tulasne. • Erysiphaceae. in] ERYSIPHALES 79 Aerial mycelium dark-coloured or rarely absent. Peri- thecia globose or ovoid, without appendages. Conidia not ofoidium type. PERISPORIACEAE. Aerial mycelium dark-coloured or absent. Perithecia flattened or shield-shaped, with an ostiole at the apex, without appendages. Conidia absent. MlCROTHYRIACEAE. A further and probably important distinction which separates the Erysiphaceae from the other two families is the character of the ascus and ascospores. In Erysipke and its allies the ascus is more or less globose, the spores are always continuous and colourless, and the number of spores in the ascus is frequently reduced. In the Perisporiaceae, on the other hand, the ascus is relatively elongated and sometimes cylindrical, and the spores are commonly two or more celled and often dark-coloured. Most species agree, however, with the Erysiphaceae in the absence of paraphyses. The Microthyriaceae approach the Perisporiaceae rather than the Erysiphaceae in the characters of the ascus and spore, but, as already stated, they are clearly distinguished by the curious flattened perithecium. It remains for future research to determine whether these families should be grouped together, or whether the Perisporiaceae and Microthyriaceae are true Pyrenomycetes and should be placed in that alliance. In our present extensive ignorance of the initiation and development of their perithecia, it seems unwise to remove them from their traditional position in the neigh- bourhood of the Erysiphaceae. Erysiphaceae The members of the Erysiphaceae are popularly known as white or powdery mildew or blight. They have a practically worldwide distribution, but have been recorded especially in Europe and the United States. They are obligate parasites on the leaves or young shoots and inflores- cences of flowering plants. The germinating conidium or ascospore gives rise to an abundant, superficial, septate mycelium of uninucleate cells, which ramifies over the leaf in every direction, forming a white web-like coating, and sends haustoria into the epidermal cells of the host. In the simplest cases the haustorium is a slender tube which swells up inside the host cell; in other species it is branched, sometimes forming finger-like processes, and frequently there is an external disc or swelling (adpressorium), from which, or from the mycelium in the neighbourhood of which, the haustorium proper arises and pushes into the epidermal cell. As a rule the fungus does not penetrate further, but in Erysiphe Graminis Salmon was able to induce endophytic growth and nutrition by allowing the conidia to germinate on wounded leaves; in Phyllactinia Corylea the branches of the aerial mycelium So PLECTOMYCETES [CH. enter the stomata, extend through the intercellular spaces and send haustoria into the neighbouring cells, and in Erysiphe (or Oidiopsis) taurica the whole mycelium during the conidial stage is located in the tissues of the host. We have thus, within the limits of the family, a transition between ecto- and endoparasitism through hemiendophytic forms, and forms which are endo- phytic under abnormal conditions. When perithecia are about to be produced and the mycelium emerges and spreads over the surface of the host leaf, the hyphae both of ' Phyllactinia and of E. taurica show haustorial branches (ad- pressoria), though no haustoria are produced. It may be inferred that the ectophytic condition with haustoria penetrating the epidermal cells is primi- tive in the group. Indian and Persian specimens of E. taurica have been found under practically desert conditions, others have been collected on plants of the steppes of Turkestan at a height of 6000 feet, and in localities exposed to very dry winds. The suggestion has consequently been made that the endophytic habit in this family is an adaptation to xerophytic conditions, since it both provides shelter for the developing mycelium and obviates the necessity of piercing through the cuticle, which in desert plants is of considerable thickness. The Erysiphaceae are propagated during the summer by rather large oval uninucleate conidia (fig. 38). These are ordinarily produced in rows on simple conidiophores with one or more basal cells. In the endophytic E. taurica, however, the conidia are borne singly on branched conidio- phores which emerge through the stomata of the host. In the case of Phyllactinia Cory- lea, which is met with on a large number of deciduous trees, variations occur in the shape of the conidia borne on different hosts, and indicate the existence of morphological dis- tinctions between the biological forms of the species. Before the connection between the conidia and the perithecia of the Erysiphaceae was understood, the generic name, Oidium, was applied to the former. The name is still used to indicate the characteristic form of the conidial stage and to describe conidia when the perithecia are unknown. This was the case with the powdery vine mildew. The conidial form, known as Oidium Tuckeri, became Fig. 38. Sphaerotheca pannosa Wallr. ; conidio- phores and conidia, x ij,o. in] ERYSIPHALES Si prevalent in Europe in 1845-6, but perithecia were not observed till 47 years later, when they appeared during two successive seasons in various localities in France, and the fundus was identified with the American vine mildew, lJiici>ii(l(i necator, in which perithecia are common. The unusual production of the perithecia] stage was attributed to the sudden alternation of high and low temperatures which characterized the seasons in question. The survival of the fungus in the absence of ascospores has been attributed to the persist- ence of the mycelium, and also to the development of conidia capable of passing the winter in the resting state. Fortunately the disease is readily kept in check by the application of appropriate sprays. A very similar case is that of the oak mildew. In or about 1904, oak scrub in England and many parts of Europe became infected with the conidial form 0. Quercinutn; in 191 1 perithecia were found in France, and the parasite was identified with the common American form Microsphaera Alni which frequently occurs on oaks in the United States. Here again exceptional seasonal conditions appear to have been necessary for the formation of the perithecial stage. In a different manner climate has affected the development of the goose- berry mildew, Sphaerotheca mors-uvae, which was introduced into Europe from America about 1900. Very numerous perithecia are developed but a considerable proportion either fail to mature or fail to survive the winter. Infection of the young sho'ots in the spring appears to depend on the earliest formed perithecia, which alone have had time to mature and lodge in the bark or between the bud scales of the host. For this reason prevention is here much more difficult than in the case of the vine mildew, since the mature perithecia are very difficult to kill and the spread of the disease must be combated by the removal of infected shoots in the autumn, or by appropriate methods of cultivation. The perithecia of the Erysiphaceae appear in the late summer or autumn ; they .in: spherical or subglobose, 50 — 30O/a(o-o5 to 0*3 mm.) in diameter and furnished with simple or branched appendages; they are fixed in position by means of a secondary mycelium. When quite young the peri- thecia appear white and glistening like the vegetative mycelium ; later they become clear yellow and finally brown in colour. Their development is by no means simultaneous, so that a considerable range of stages can often be seen within the field of an ordinary hand lens. During development the wall of the perithecium is differentiated into inner and outer layers (fig. 39). The inner layer is several cells thick ; its cells are rich in cytoplasm with thin, apparently unmodified walls; it is in contact with the developing asci, about which it forms a packing, and to which it supplies food material. Outside this layer is a strengthening and protective zone of several series of cells with scant}' contents, the walls of G.-V. 6 82 PLECTOMYCETES [CH. Fig. 39. Erysipke Polygoni; young perithecium containing uninucleate asci ; after Harper. which undergo a change apparently analogous to lignification. \\\ Phyllactinia the outermost layer, from which the secondary mycelium and the character- istic appendages are derived, consists of thin-walled cells, but in other genera it is not differentiated from the pro- tective zone. A single ascus or several may be formed in the peri- thecium ; the ascospores, numbering two to eight in each ascus, begin to develop during the summer or au- tumn, but they remain in the perithecium under nor- mal conditions and do not germinate till the beginning of the following year, when they are set free by the rupture of the perithecium wall, and produce the first infections of the season. In Erysiphc Graminis and Sphaerotheca mors- uvae some of the perithecia separate readily from the mycelium in August, and, if supplied with moisture, will eject their spores after a few hours. They may in this way prove a source of infection in the season in which they were produced, and this is probably true of other species also, and should be borne in mind if ripe ascospores are being searched for. The family includes six genera, all of which are British, and are readily distinguished (fig. 40). In Sphaerotheca (one ascus), and in Erysipke (several asci), the perithecial appendages are filamentous, unbranched or branched irregularly, and very like the ordinary hyphae of the mycelium ; in Podcsphaera (one ascus), and in Microspliaera (several asci), they are usually dichotomously branched ; in Uncinula the apices of the appendages are spirally coiled, and in Phyllactinia the perithecium bears stiff, pointed hairs with swollen bases. In this genus also the apex of the perithecium is furnished with a ring of richly branched penicillate cells. At about the time of spore-formation these break down, forming a sticky gelatinous cap, by means of which the perithecium, after it is first set free, adheres upside down to its original host plant or to other objects. In view of this peculiarity the ascription of Phyllactinia to any host in contact with which its perithecia may be found demands careful veri- fication. The function of the true appendages in the Erysiphaceae is somewhat variable. In Phyllactinia the bulb at the base of the appendage is thick- Ill] ERYSIPHALES 83 walled over its upper surface, but an oval region remains thin on the lower side. As the ripening perithecium loses water so do the appendages; the thin area below the bulb is pushed in by atmospheric pressure, the under surface becomes consequently shorter than the upper and the end of the spine is [lulled down till subsequent moistening straightens it again ( Harper). Fig. 40. Perithecia of a. Erysiphe tortilii (Wa.llr.) IV.: b. Microsphaeria sp.\ c. Uncinate Aceris (DC.) Sacc. ; d. Phyllactinia Corylca (Pers.) Karst. ; x 120. These hygroscopic movements may be repeated many times according- to weather conditions, even after the living protoplast has disappeared from the appendage (Xeger); and af last the perithecium is loosened from its attachment. In other cases, such as Erysiphe and Sphaerotheca, the appendages ma}' help to anchor the perithecium to its host during development; in Uncinula necator their apices become mucilagini >us < Salmi >n ), and they serve, much as do the penicillate cells of Phyllactinia, to attach the free perithecium upside down to the substratum. The development of the perithecium was first described in 1863 by 6—2 . 84 PLECTOMYCETES [CH. de Bary, who was able to recognize an antheridium and oogonium and the formation of an ascus or asci from the latter. These and several subsequent investigations have rendered the reproductive processes in the Erysiphaceae better known than perhaps in any other group of fungi. Spliaerotlieca Humuli* occurs on a variety of common plants, on the cultivated strawberry, where it is responsible for strawberry mildew, and especially on the hop. On the latter it is widely distributed in autumn, and, if the female inflorescences are infected, may do considerable damage. The male and female organs arise as lateral branches from the mycelium, and project at right angles to the infected surface; they are borne on dif- ferent hyphae, but there is no evidence that these are derived from distinct mycelia. The oogonium, when fully grown, is an oval, uninucleate structure two or three times the size of an ordinary vegetative cell; it is cut off from the parent hyphae and a stalk cell may be differentiated below it (fig. 41 a). Fig. 4 1 . Sphaerotheca Humuli (DC.) Burr.; a. young oogonium and antheridium ; b. entrance of male nucleus; c. male and female nuclei in oogonium; d. fertilization; e. fusion nucleus; f. nuclei produced by first division of fusion nucleus; g. young perithecium with binucleate ascogenous cell; x 1360; after Blackman and Fraser. 1 S. Humuli (DC.) Burr. = 5. Castagnei Lev. Ill] ERYSIPHALES The antheridial branch is much narrower; it applies itself to the side of the oogonium and when first cut off contains a single nucleus (tig. 41 ), the male nucleus passes into the oogonium, travels to the female nucleus and fuses with it (fig. 41 c,d). The pore between the sexual cells soon closes and the cytoplasm left behind in the antheridium degenerates, sometimes forming a densely staining cap on the oogonium. The fertilized oogonium elongates, the fusion nucleus divides (fig. 41 f) and a wall separates the daughter nuclei so that two uninucleate cells are formed. The upper divides again and eventually a row of cells is produced, the penultimate con- taining two nuclei while the others are uninucleate (fig. 41 g). The formation of the first wall is sometimes delayed, so that the undivided oogonium may for a time show two or three nuclei. At about the time when the sexual organs reach maturity the develop- ment of the sheath begins, branches grow out from the stalk of the oogonium and enclose the sexual organs in a single layer of cells. These give off branches towards the interior, and thus a second zone is formed whose cells become rich in cytoplasm and contain two or three nuclei each. The nutritive and protective envelopes are thus laid down and their further de- velopment produces the typical sheath already described. Meantime the penultimate cell of the septate oogonium enlarges to form the single ascus characteristic of Sp}taerotheca% the terminal cell and tin cells below the ascus are pushed aside and disappear, the two nuclei fuse, the usual three successive nuclear Fig. 4:. Sphaerotheca Hamuli (DC.) Burr.; de- d- • ■ .1 1 1 velopment ofarchicarp; in <". two nuclei, re- .visions take place, and ascospores garded as the productTfdivision, are shown fn arc produced. oogonium, while a cell at the top ol the .... , , r ., u r oogonium, regarded as the antheridium, .nil 1 he only record of the number 1 if contains a nucleus; after Winge. 86 PLECTOMYCETES [CH. chromosomes is that of Winge who describes eight in the first and second mitoses, and four in the third, and suggests that a brachymeiotic reduction takes place. According to the interpretations of Dangeard and Winge fertilization does not take place in the oogonium of Sphaerotheca Hamuli. For them the degenerating mass in the antheridium includes the male nucleus which thus degenerates in situ and the two nuclei seen lying side by side in the female organ represent the product of a premature division (fig. 42). Again Bezssonoff working on Sphaerotheca mors-uvae, the economically important gooseberry mildew, records the entrance of the male nucleus into the oogonium, but does not observe its fusion with the female nucleus. He finds four chromosomes throughout the divisions in the ascus. Erysiplie Polygoni'1 occurs on the leaves and stems of a considerablevariety of hosts belonging to a number of different families. The development of the sexual organs takes place much as in Sphaerotheca Hamuli, and, here also, Harper has observed the entrance of the male nucleus into the oogonium, and its fusion with the female nucleus (fig. 43«). After fertilization the Fig. 43. Erysiplie Polygoni; a. fertilization; d. young perithecium with ascogenous hyphae ; after Harper. protective hyphae begin to grow up, the oogonium elongates, the fusion nucleus divides till a row of from five to eight nuclei is produced, transverse walls appear, and a row of cells is formed of which the penultimate contains two or more nuclei. From the surface of the penultimate cell, and perhaps sometimes from that of its neighbours, filaments bud out (fig. 43^), branch rapidly to form a dense mass, and undergo septation. These are the ascogenous hyphae. In them some six or eight intercalary cells, which will give rise to asci, become distinguished by the fact that each contains two nuclei. The rest 1 Erysiplie Polygoni ~DC. = Erysiphe communis (Wallr.) Link and Rabh., and E. Martii Lev. Ill] KRYSIPIIALES 87 lose their contents and are displaced by the developing asci. Later the fusion of the two nuclei in each ascus takes place, and in each eight spores are formed. Dangeard, investigating the development of /:. /'o/yyii/ and /:'. Cklw- racearum, notes that in his material the oogonium underwent septation before a row of nuclei was formed, and that cells other than the penultimate contained two or more nuclei. Usually in E. Cichoracearum and sometimes in E. Polygoni the oogonial branch consisted of two cells; this corresponds with the arrangement in the antheridial branch, which is regularly bicellular. In both cases the lower cell is to be regarded as a stalk. In regard to the occurrence of fertilization Dangeard's conclusions correspond with those which he reached in relation to Sphaerotheca. Phyllactinia Corylea infects the leaves of deciduous trees and shrubs in- cluding ash, oak, beech, hazel and hornbeam. The sexual organs arise (Harper 1905), as in other mildews, where two hyphae intersect. They become closely applied to each other, and, as the oogonium grows more quickly than the antheridial branch, it becomes some- what twisted around the latter. The subsequent history is very like that of Sphaerotheca or Erysiphe. A uninucleate antheridium is cut off, the male nucleus enters the female organ (fig. 44^), nuclear fusion takes place, the Fig. 44. Phyllactinia Corylea (Pers.) Karst.; a. fertilization; b. fusion nucleus in oogonium ; c. \\ 1 1 3, E. L. The Curl of Peach Leaves ; a Study of the Abnormal Structure produced by Exoascus deformans. Bot. Gaz. xii, p. 216. 1894 DANGEA.RD, P. A. La reproduction sexuelle des Ascomycetes. Le Botaniste, iv, p. 30. 1903 Ikeno, S. Die Sporenbildung von Tapftrina-Aiten. Flora, xcii, p. 1. CIIAl'TI'K IV IHSCOMVCETES THE term Discomycctes is applied to those groups in which the fruit is more or less cup-shaped (fig. 51), with the hymenium fully exposed at maturity, and t<> their immediate allies. The ascocarp is surrounded by a peridium or sheath of closely interwoven hyphae which is closed at first and later is pushed apart by the paraphyses, so that at last it forms the outer Fig. 51. Otidta aurantia Mass.; apotheci, Fig. 52. Lachni ,m in Pyronema and in Lachnea stercorea, and we have also, if its position Fig. 55. Sepultaria coron M uniseriate spores ; ascus opening by a lid; branched, septate, clavate paraphyses ; x 600. 7 98 DISCOMYCETES [ch. should be ultimately established, the curious stalked conidium of Ascobolus carbonarius. The archicarp is of much commoner occurrence, and seems more likely to be useful as a gauge of relationship. Among Discomycetes the simplest type is undoubtedly that of Ascodesmis or Thelcbolus; the significant details in Thelebohis are not fully known, but in Ascodesmis we have a stout, twisted hypha, divided into three parts, the unicellular trichogyne, the unicellular coenocytic oogonium and the multicellular stalk (fig. 56). After fertilization Fig. 56. Ascodesmis nigricans Van Tiegh.; sexual apparatus; a. trichogyne; b. antheridium; c. oogonium; (/. stalk; e. gametophytic hypha ; after Claussen. Fig. 57. Pyronema confluens; spherical oogo- nium giving rise to ascogenous hyphae; a. an- theridium ; /'. trichogyne; c. oogonium ; d. as- cogenous hyphae; x 1040; after Clau6sen. the oogonium becomes septate, so that the fertile part is multicellular and the ascogenous hyphae arise from several cells. This type closely approxi- mates to that in Eurotium and some other Plectascales, and there seems reason to regard it as a primitive female organ among Discomycetes. From it may be derived the spherical oogonium of Pyronema (fig. 57) which differs mainly in the fact, no doubt connected with its shape, that it does not become septate after fertilization, so that the ascogenous hyphae arise from one cell only. The same is true of Lachnea stercoral, which iv] DISCOMYCETES 99 differs in its multicellular trichogyne, and of Humaria granulata, and perhaps some other forms in which the trichogyne, like the antheridium, has dis- appeared. Another group is distinguished by the multicellular oogonial region of the archicarp, which has also a stalk and a terminal region (or trichogyne) of several cells each (fig. 58). This type of female organ is sometimes termed a scolecite. It occurs in Lachnea cretea and in several species of Asco- bolus and Ascoplianus. In Ascobolus furfuraceus several of the central cells communicate one with another by means of pores, but only one of them gives rise to asco- y ° Fig 58. Ascobolus Jitrjui genous hyphae; in some other species of Asco- ivr'-..; archicarp, x;4o; after bolus and in the genus Ascophanus ascogenous '"' ye' hyphae arise from several communicating cells; the same is true of Lachnea cretea, where three or four cells become practically continuous owing to the disappearance of the transverse septa between them. In the trichogyne also, or terminal region of the archicarp, pores are formed in the transverse walls, so that this multicellular organ offers no bar to the passage of male nuclei. Such structures may well have been derived from the Ascodesmis type by the elongation and transverse septation of the parts of the archicarp. Our knowledge of the sexual organs of the Pezizales thus suggests that they may have been derived, along two principal lines of development, from a common ancestor within the group. In only two other families of Discomycetes, the Rhizinaceae (Rhisina and Sphaerosomd) and the Geoglossaceae (Leotia) has an oogonium been recognized. In each of these a large fertile cell is present, but its develop- ment is not known and no suggestions as to phylogeny can therefore be based upon it. Our knowledge of the development and especially of the reproductive organs of the Discomycetes is still very incomplete and further research is very necessary. As has been shown in Leotia, Humaria and other cases, it by no means follows that because one member of a genus has lost its sexual apparatus the same will be true of others. Every available species should be investigated. The Discomycetes include over 4000 species and may be subdivided as follows : Hymenium fully exposed at maturity mature ascophore cup-shaped Pezizai 1 in. nine ascophore reflexed or stalked with the fertile region often convoluted 1 1 1 I VELLALES. 7—2 ioo DISCOMYCETES [ch. Hymenium incompletely exposed at maturity ascophore round, aperture usually stellate Phacidiales. ascophore elongated, opening by a slit HYSTERIALES. Hymenium enclosed at maturity Tuberales. Pezizales The Pezizales are characterized by the fleshy or sometimes leathery ascocarp, bounded, except in the Pyronemaceae, by a more or less definite peridium which is closed at first and opens later, giving the mature fruit a cup or saucer shape. This dehiscence is due to the growth of a conical mass of paraphyses which push out at the apex of the ascocarp. Fresh paraphyses and, a little later, asci grow up amongst those first formed and the peridium is pushed wide open and the hymenium exposed. The asci contain usually eight, but sometimes four, sixteen, thirty-two, or numerous spores, which germinate typically by means of germ-tubes, but which, in a few cases, give rise by budding to conidia. Various accessory spores, including conidia, chlamydospores and oidia, are also produced. The mycelium is well developed and filamentous, rarely forming a scle- rotium. The species are parasitic or saprophytic on the ground or on dead parts of plants ; in many cases they are coprophilous. Considering the very large size of the group the number of species investigated is small. In a few of these, normally functional male and female organs have been found, in some the antheridium has disappeared, and in many the oogonium is also lacking. Where an oogonium is present it gives rise to the ascogenous hyphae, while the paraphyses originate from the stalk or from the surrounding cells (fig. 52). The group may be divided into the following families : Peridium continuous with hypothecium Peridium incomplete; ascocarps usually compound PYRONEMACEAE. Peridium well-developed asci not rising above the surface when ripe ; asco- spores usually uniseriate PEZIZACEAE. asci rising above the surface when ripe ; ascospores often coloured and biseriate Ascobolaceae. Peridium distinct from hypothecium Peridium of elongated hyphae (pseudoprosenchymatous) HELOTIACEAE. Peridium pseudoparenchymatous MOLLISIACEAE. Peridium absent or ill-defined ; epithecium formed CelidiaCEAE. Peridium tough ; epithecium formed ascocarp free Patellariaci \i ascocarp embedded when young CENANGIACEAE. Apothecia numerous, sunk in a stroma Cyttariaceae. IV] PEZIZALES 101 Pyronemaceae The Pyronemaceae arc a small group distinguished from the other Pezizales by the fact that the pcridium, or lateral boundary of protective hyphae around the fruit, is not well developed. This is not always regarded as a sufficiently important character to warrant their separation from the Pezizaceae and many authors include them in that group. The only important genera are Ascodesmis and Pyronema, species of both of which have been somewhat fully investigated. Ascodesmis nigricans'1 (fig. 59) is a small coprophilous form. The sexual organs appear in artificial culture about forty-eight hours after the germination of the spore. Stout, multinucleate hyphae grow up from the mycelium and dicho- tomize (fig. 60a) to give rise to some six or eight archicarps. Near these, and usually from the same filament, one or two antheridial hyphae arise. They grow towards the archicarps (fig. 60^) and dichotomize (fig. 60c), while around each of their terminal cells or antheridia, an archicarp becomes wrapped (fig. 60 d). In the meantime walls are laid down, so that the various archicarps and antheridia become cut off from their neighbours, and each archicarp divides transversely to form a tri- chogvne and an oogonium. The trichogyne usually contains two nuclei, the oogonium five or six and the antheridium about the same number. The nuclei of the trichogyne soon degenerate, and, as observed by Claussen, the wall between this cell and the antheridium is broken down (fig. 60 e), so that open communication is established. The male nuclei pass into the oogonium, where for a time ten or twelve nuclei may be counted, then fusion of these in pairs takes place (fig. 60 f). Subsequently the oogonium enlarges somewhat and undergoes septation ; large ascogenous hyphae, usually about three in number, hud out from it (fig. 60^), and quickly give rise to asci (fig. 60/1). Ascus formation is apparently quite typical, the spores are spherical and have a characteristically sculptured epispore (tig. 60/). At Fia ;i). Ascodesmis nigricans Van Tiegh.; apo- thecium, x 540; after Claus n. 1 Claussen described the cytology "I this species under ilie name of Boudiera ii ' n • Karst. ; seeCavara, Ann. Myc. iii, 1905, p. .56,5, and Dangeard, Botaniste, \. Tyo;. p. 247, for nomenclature. 102 DISCOMYCETES [ch. about the time of fertilization vegetative filaments begin to grow up (fig. God), and at last form a loose investment around and among the developing asci (fig- 59)- Fig. 60. Ascodamis nigricans Van Tiegh.; a. b. c. d. development of the sexual apparatus; a. and b. x 1000, c. x 1 100, d. x 800 ; e. communication between antheridium and trichogync, x 1300; /".fusion in oogonium, x 1600; g. septate oogonium and ascogenous hypha ; antheridium and trichogyne shrivelled, xiooo; //. uninucleate ascus, xnoo; /. sculptured spores in ascus, -750; alter Ciaussen. Pyronema confluens1 occurs on burnt ground or on charred and decayed leaves in woods. Its fruits are pink or salmon-coloured, its mycelium to a great extent superficial, and its sexual apparatus of unusually large size. The latter fact led to an early study of its development. It was described by de Bary in 1863, by the brothers Tulasne in 1865 and 1866, by van Tieghem in 1884, and by Kihlman in 1885, and a very clear understanding of the morphology of the sexual organs was reached. A swollen, elongated antheridium was recognized and a more or less globular 1 Pyronema confluent. Tul. = P. omphaloides (Bull.) Fuckel. IV PKZIZALHS 10: oogonium, from which a trichogyne protruded (fig. 61 />). The union of the trichogyne and antheridium was observed and it was shown that from the oogonium ascogenous hyphae subsequently arose. Van Tieghem recorded that the species is very susceptible to external conditions, the antheridium sometimes being reduced in size or absent, though the oogonium nevertheless developed normally and produced ascogenous hyphae. In 1900 appeared the classical researches of Harper, followed in 1903 and 1907 by Dangeard's, and in 1912 by Claussen's investi- gations. The mycelium is made up of cells of varying length, regularly multinucleate, containing six to twelve nuclei, and filled with cytoplasm of a loose, spongy structure. The mycelium is sparse and loose, but the reproductive organs are very abundant so that the ascocarps, when mature, are often crowded together. The first indication of sexual reproduction consists in the appearance of thick hyphae, very similar to the corresponding filaments in Ascodesmis, and tending, like them, to stand at right angles to the substratum. They dicho- tomize (fig. 61 a), the terminal cells become swollen, and two types, the more spherical oogonium and the more elongated antheridium, are distinguished; these arise on separate branches, but from the same mycelium. Both are multinucleate from their initiation. Very soon a slight elevation appears on the oogonium; it elongates rapidly to form the multinucleate trichogyne and, before its growth is complete, is separated from the oogonium by a wall; the trichogyne and antheridium grow towards one another, the tip of the trichogyne meeting sometimes the apex, but more commonly the flank of the male organ. The mature oogonium is a spherical or flask-shaped cell filled with dense-cytoplasm and containing many nuclei which are very much larger than those of the ordinary vegetative cells. Its stalk consists of two or three broad cells, its apex is continued into the trichogyne. The nuclei of the latter increase but little in size and are thus much smaller than those of the essential organs at maturity. The nuclei of the antheridium are almost as large as those of the female cell, but its protoplasm is less dense owing perhaps to the absence of accumulated reserve materials. It would appear Fig. 61. Pyronema con/luens Tul.; a. development of sexual apparatus; b. mature oogonia ami antheridia ; x 390; after de Bary. 104 DISCOMYCETES [CH. that in both oogonium and antheridium some nuclei degenerate (Claussen). Hyphae from the ascogonial and antheridial branches, and also from the surrounding cells, begin to grow up even before fertilization, and later envelop the sexual organs. When fertilization is about to take place an area of cytoplasm in the region of the antheridium, against the wall of which the tip of the trichogyne is pressed, is differentiated as a very finely granular disc from which the nuclei are withdrawn. Although located in the antheridium this area resembles the receptive spot seen in the oosphere of many algae. The tip of the trichogyne has by this time developed as a beak-like projection, and this also is empty of nuclei and contains dense and finely granular cytoplasm. The walls of the antheridium and trichogyne now break down at the point of contact and a pore is formed. The process is gradual, consisting probably of a softening and solution of the wall material, which seems to Fig. 62. Pyromma conjluens; a. antheridium, trichogyne and oogonium, male and female nuclei collected in the middle of the latter ; b. c. fusion of male and female nuclei; after Harper. spread out into the cytoplasm of the beak, suggesting that the solvent action is mainly exerted from the interior of the trichogyne. The open pore now becomes thickened around its margin so that an exceedingly strong ring unites the antheridium and trichogyne, and they can be bent or turned upon each other without being pulled apart. This arrangement is no doubt necessary to withstand the strain set up by the flow of nuclei from the relatively wide cavity of the antheridium through the narrow pore and beak. IV I PEZIZALES 105 While the formation of the pore is in progress the nuclei of the tricho- gyne degenerate, and, by the time that they are completely disorganized, a migration of the male nuclei through the pore begins. Ultimately the contents of the trichogyne degenerate still further, till the cytoplasm and nuclei together form a densely staining mass which maybe recognized even in the mature fruit. The male nuclei continue to pass into the tube until it is densely filled, and sometimes a trifle swollen. According to most observers the wall at the base of the trichogyne now breaks down so that an open passage is formed and the male nuclei travel through (fig. 63 a), and mingle Fig. 63. Pyronema confluens; a. entrance of male nuclei into oogonium, x 14.^=: b. association of male and female nuclei, xitfjo; <'• ascogenous hyphae with nuclei in pairs, X820; after ( )laussen. with the female nuclei. After their migration is complete a fresh wall is laid down across the base of the trichogyne, cutting off the oogonium once more as a single spherical cell. The female nuclei meantime become aggregated together (fig. dia) and form a hollow sphere or dome or a sickle-shaped group. This is no doubt a provision for insuring their association with the male nuclei with the greatest certainty and dispatch. According to both Harper and Claussen, the sexual nuclei now pair; I [arper has recorded complete fusion at this stage (fig. 62b), while Claussen (fig. 636) regards the nuclei as merely associated in preparation for their ultimate union in the ascus. Dangeard, on the other hand, denies the dis- appearance of the wall between the oogonium and trichogyne or the passage of the male nuclei beyond the latter organ, and Brown has described a variety in which the trichogyne and antheridium fail to unite. io6 DISCOMYCETES [ch. In any case the greater part of the male cytoplasm does not enter the oogonium but is left behind in the antheridium and trichogyne ; con- sequently these organs, after their function is complete, remain, to the superficial view, unchanged for a long period, till they are crushed at last by the growth of the investing hyphae, or perhaps destroyed by bacteria (Harper, p. 354). Before the stages described above, the oogonium has begun to bud out (fig. 62a) at various points, giving rise to the ascogenous hyphae. Into these the nuclei pass, a few, no doubt unpaired, being left behind in the oogonium. The hyphae elongate, branch freely and undergo septation, and, as the vegetative filaments grow up, they ramify among them and at last bend over and give rise to asci from their penultimate cells. Claussen has described a paired arrangement of the nuclei in the ascogenous hyphae (fig. 63c), and believes the members of each pair to be respectively male and female. After the ascogenous and vegetative hyphae are thoroughly interwoven, a rapid stretching upward of the whole mass ensues. In this growth the vegetative hyphae outstrip the reproductive ones, and form at first a cone- shaped mass, made up of their elongated, slender, densely aggregated tips. These upper extremities of the vegetative hyphae are the young paraphyses. Their number is constantly increased by the pushing in of new branches from below, and thus the conical outline of the mass is maintained. The ascogenous hyphae grow for a certain distance in company with the vegetative filaments, then their upward growth ceases, and they spread out horizontally, forming a rather dense layer below the cone of paraphyses. This is the base of the hymenium. Usually in Pyronema, as in Ascodesmis, several oogonia are invested by a common sheath, and their ascogenous hyphae mingle to form the hymenium of a single ascocarp (fig. 64), but ascocarps developed in relation to a single pair of sexual organs are not unknown. The formation of the asci in Pyronema is quite typical. The number of chromo- somes is probably ten (Harper), or twelve (Claussen), at any rate in the first divisions in the ascus. Dangeard records a smaller number in the third division, and in the variety inigneum Brown describes five throughout. Fig. 64. Pyronema confluens; diagram- matic section through ascocarp ; after Harper. iv] PEZIZALES 107 As development proceeds the sexual organs become completely crushed and are at last no longer recognizable. At an early stage it becomes impossible to trace the connection between the ascogenous hyphae and the oogonium, and, during a great part of their development, these depend for their nutrition upon the paraphyses and other vegetative cells. A secondary mycelium grows downwards to the substratum, obtaining food material from it and serving for the attachment of the mature ascocarp. Special storage cells appear in the hypothecium. PYRONEMACEAE: BIBLIOGRAPHY 1863 DE BARY, A. Entwickelungsgeschichte der Ascomyceten. Leipzig. 1865 TULASNE, L. R. and C. Selecta fungorum Carpologia, iii. Imperial, typography Paris. 1866 Ti'I.asnk. L. R. and C. Note sur les phenomenes de copulation que presentent quelques Champignons. Ann. Sci. Nat. vi, p. 217. 1884 v.w TlEGHEM, Ph. Culture ct dcveloppcmcnt du Pyronema confluens. Bull. Soc. Bot. de France, xxxi. p. 355. 1885 Kim. max, O. Zur Entwickelungsgeschichte der Ascomyceten. Pyronema confluens. Acta Soc. Sci. Fennicae, xiv, p. 337. 1900 HARPER, R. A. Sexual Reproduction in Pyronema confluens, and The Morphology of the Ascocarp. Ann. Bot. xiv, p. 321. 1905 Cl.Af.ssKN, P. Zur Entwickelungsgeschichte der Ascomyceten. Boittiiera. Bot.Zeit. lxiii, p. 1. 1907 DANGEARD, P. A. Recherches sur le developpement du perithece chez les Ascomy- cetes. Le Botaniste, x, pp. 247 and 259. 1909 Brown, W. H. Nuclear Phenomena in Pyronema confluens. Johns Hopkins Univ. Circ. vi, p. 42. 191 2 Ci.Af.ssEX, P. Zur Entwickelungsgeschichte der Ascomyceten. Pyronema confluens. Zcitschr. f. Botanik, iv, p. 1. 1915 BROWN, W. H. The Development of Pyronema confluens, var. inigneum. Am. Journ. Bot. ii, p. 289. Pezizaceae The Pezizaceae form a rather large group. The ascocarp is superficial, sessile or stalked, usually with a well-marked peridium fleshy or waxy in consistency, and soon decaying after maturity. The spores are usually hyaline and continuous (though septate in some small species) and are typically uniseriate. The asci do not project above the level of the disc at maturity, as they do in the Ascobolaceae. The species are mostly sapro- phytic, many occurring on the ground, and a few, especially the smaller forms, on dung. The subdivisions depend on the shape of the spores, the size and consistency of the ascocarp, and the presence or absence of hairs. [n the majority of forms the fruit is fleshy and without hairs: these species are often grouped together in the single genus Peziza, but it is probably more convenient to separate them. The name Peziza is retained for large species with ,1 sessile or subsessile cup, regular in form and two ioS DISCOMYCETES [CH. centimetres or more across as in P. vesiculosa. The genus Humaria includes similar but smaller species, often less than one centimetre in diameter. In Otidea the sides of the ascophore are laterally split, or vertically incurved and wavy. In Acetabula and Gcopyxis the ascophore is stalked. In Lachnea, as well as in some other genera, the fruit is beset with hairs and in Sepultaria it is hairy and more or less sunk in the soil. Lachnea stercorea is a small orange species occurring during the winter and spring on the dung of various animals, especially of cows. With Humaria graimlata and Ascobolus furfuraceus, it is among the very common coprophilous forms, appearing in many parts of Britain with great regularity when the Piloboli have died down, and the cow pad is beginning to dry. It is about 4 mm. in diameter and is furnished with numerous stout, septate hairs. The archicarp arises as a side branch from the vegetative mycelium, and divides to form four or more cells. The terminal cell or oogonium is oval in shape and larger than the others. It contains between two and three hundred nuclei and is filled with finely granular cytoplasm. In the cell next below the oogonium, the cytoplasm is also more dense and the nuclei more numerous than in the other cells of the fertile branch. Hyphae grow up from the lower cells of the archicarp, and from the branch which bears it, and form a dense weft above which the oogonium rises. Fig. 65. Lachnea stercorea (Pers.) Gill.; a. young archicarp, x 800; b. archicarp and antheridiuin, x 500; P. Highley del. The oogonium sends out either laterally, or from its apex, a stout branch or trichogyne. It is cut off by a wall and divides into four to six cells, the terminal of which is much larger than the others (fig. 65a). The tip of the trichogyne protrudes for a time beyond the developing sheath, but later, w^ith the whole fertile branch, it is enclosed by vegetative hyphae. iv] PEZIZALES 109 At this stage a large, more or less oval sac is often found to be continuous with the terminal, or receptive, cell of the trichogyne into which a proportion of its contents pass (fig. 6$6). There seems no doubt that this sac is the antheridium, but its development is not known, and there is no evidence that its contents ever pass beyond the receptive cell of the trichogyne. Indeed all the a\ ailable evidence shows that both antheridium and trichogyne are now merely vestigial structures. Nevertheless the development of the oogonium continues, its nuclei increase to something over 500 in number, and ascogenous hyphae bud out. Before passing into these the oogonial nuclei fuse in pairs, so that normal fertilization is here replaced by the union of female nuclei. The ascogenous hyphae branch and give rise to asci, in each of which eight spores are produced in the usual way. The karyokinetic figures are small but very clear, there are four chromosomes in the first and second divisions, but in the third telophase only two have been recorded. There is some evidence that the chromosomes show regular and characteristic differences of form, which reappear in successive divisions. The peridium, though much better developed than in the Pyronema- ceae, is never completely closed, as in Humaria or Ascobolns, across the top of the ascocarp. The paraphyses are numerous and contain orange granules. Lachnea scutellata occurs on decaying wood, forming bright red apothecia. The archicarp consists of seven to nine cells, the subterminal of which enlarges to form the oogonium. The nuclei in this cell divide, and, according to Brown, show five short, stout chromosomes. He did not observe nuclear fusion or association in the oogonium, but regards the nuclei lying in contact as the two daughter nuclei of a single mitosis. Large ascogenous hyphae develop, undergo septation, and branch freely. Their tips bend over and asci are formed in the usual way from the penultimate cells. The terminal cells may undergo further growth and give rise, as in several other Disco- mycetes, to new asci. Nuclear fusion takes place in the young ascus, and is followed by a meiotic reduction. Five gemini are recorded, but, in the anaphase of the first division, ten chromosomes travel towards each pole. This Brown takes to indicate an early fission of the daughter chromosomes. In the second and third divisions five chromosomes are seen throughout. Brown infers the occurrence of a single fusion in this species, that in the ascus, and a single reducing division1. Lachnea cretea has a pale buff apothecium, beset with hairs (fig. 66a). It has been found on plaster ceilings, and, like many other saprophytic species, grows readily in artificial culture. 1 The magnification of Brown's figures of the divisions in the oogonium is enormous (x 11,100), and their details should therefore probably be received with some caution. I IO DISCOMYCETES [CH. The archicarp (figs. 66 b-e) consists of a long, branched, multicellular trichogyne, an oogonial region of three or four coenocytic cells, and a multicellular stalk. No antheridium has been observed. In the trichogyne (fig. 66 e), pores are formed between the adjacent cells, and are closed after a time by "callus" pads. In the central part of the archicarp the transverse septa are completely broken down, so that a very wide passage is formed, and nuclei pass readily from cell to cell (fig. 66/). All the cells give rise Fig. 66. Lachiua cretea Phi!.; a. mature ascocarp, xoo; b. <"■ development of archicarp, X300; d. older archicarp showing crowded nuclei, x 400 ; e mature archicarp with elaborately branched trichogyne, x 400;/'. three ascogonial cells united by very large pores, X400. to ascogenous hyphae. Thus the oogonial region, though developmental ly multicellular, is for all practical purposes unicellular at maturity, and offers no greater difficulties in the way of fertilization than the oogonium of Pyroncma itself. The branched character of the trichogyne is exceptional among Disco- mycetes ; it might, no doubt, facilitate the establishment of contact with an iv] PEZIZALES in attached antheridium if the latter developed at a distance. But branching might also be regarded as a secondary or vegetative development, appearing after normal fertilization had i ea led to occur. The presence of pores in the transverse septa of the trichogyne suggests that the function of that organ in relation to an antheridium has only recently been lost. Fig. 67. Humaria granulata Quel.; young archicarp, X320; after Blackmail ami Fraser. The ascogenous hyphae contain many nuclei irregularly arranged. Asci in- formed in the usual way; their nuclei show about eight chromosomes in the first division. Owing to the small size of the nuclei further cytological details have not been studied in this species. 112 DISCOMYCETES [ch. Humaria granulata is a common red or orange coprophilous form. The archicarp develops as a side branch from an ordinary hypha. The apical cell of this branch increases in size and becomes spherical, forming the oogonium (fig. 67) ; it contains large numbers of well-marked nuclei. When it is full grown the oogonial nuclei fuse in pairs (fig. 68 a), and the fusion nuclei pass into the ascogenous hyphae (fig. 68 fi). There is no sign of either trichogyne or antheridium. Fig. 68. Humaria granulata Quel. ; a. fusion of nuclei in oogonium, X3200; ^.oogonium giving rise to ascogenous hyphae, x isjo; after Blackman ami Fraser. Vegetative cells grow up and invest the archicarp, forming a close pseudoparenchymatous sheath in which the ascogenous hyphae ramify. They give rise at last to asci in the usual way. Four chromosomes have been recorded in the ascogenous hyphae, eight in the first division in the ascus and four in the two subsequent IV] I'KXIZAI.KS 1 1 • mitoses. This implies that the gametophytic number is four, and that the gemini are formed immediately after the fusion in the oogonium, so that in the ascogenous hyphae there are four bivalent instead of eight univalent chromosomes. In the meiotic prophase which follows the fusion in the ascus, there is a double number of gemini, since two sporophytic nuclei have united. In Humaria granulata, the antheridium has disappeared and normal fertilization is replaced by fusion of female nuclei in pairs in the oogonium. Fig. 69. Humaria rutilans (Fr.) Sacc; very young ascocai p, x soo. In another species of this genus, Humaria rutilans1, reduction has gone yet further and not even an archicarp is produced. The apothecium arises as a dense weft of tangled filaments, which for a time differ from one another only in the relatively thick walls of the outer hyphae, and the richer proto- plasmic content of the inner (fig. 69). Each cell of the weft contains one or a few nuclei. After a while the nuclei in the central part of the mass may be seen to be of two sizes, and the smaller have been found to fuse in 1 Humaria rutilans |Kr.| Sacc. = Peziza rutilans Fr. in Boudier, horn r, PI. 315. G.-V. 8 H4 DISCOMYCETES [CH. pairs (fig. 70 a), giving rise to the larger. Sometimes in connection with this process a nucleus migrates through the wall from one cell to another (fig. 70 b), as in prothallia of ferns. Thus in H. rutilans, where the sexual organs are completely lacking, normal fertilization is replaced by the union of vegetative nuclei in pairs. Pig. 70. Humaria rutilans (Fr.) Sacc; a. fusion in a vegetative hypha; b. migration of nucleus from one vegetative cell to another; both x 1100. The cells which contain fusion nuclei now "ive rise to ascoffenous hyphae, while, from the rest, the paraphyses and cells of the outer sheath arise. The asci are very large, and their nuclei particularly clear. The number of chromosomes in the nuclei of the ascogenous hyphae, and in the first and second divisions in the ascus and in the prophase of the third is sixteen (figs. 71, 72). In the third telophase eight have been recorded by Maire and by Fraser (fig. 73), and sixteen by Guilliermond (fig. 74). Fig. 71. Humaria rutilans (Fr.) Sacc; a. asco- genous hypha showing sixteen chromosomes in each nucleus, x 1950; b. fusion nucleus of ascus passing out of synapsis, x 1300; c. fusion nucleus of ascus showing sixteen gernini, x 1950. IV] PEZIZALES i i In several other members of the Pezizaceae, for example in Peziza vesiculosa I Fraser and Welsford) and Peziza tectoria, development appa- rently takes place, as in Humaria rutilans, without the formation of sexual organs. In Otidea anrantia (Fraser and Welsford), a large cell, no doubt part of an archicarp, has been recorded in the early stages, and in Peziza thele- boloides, Humaria Roumegueri, and //. carbonigena, there is a well-marked oogonial region of one or more cells. -' ■'.''-. '.-'•<../"<, uv&f Fig. 7:. Humaria rutilans (Fr.) Sacc; a. telophase of second division in ascus, 3370; b. prophase of third division in ascus, showing sixteen curved chromo- somes, < 2N0S. Fig. ',.'•■ Humaria rutilans (Fr.) Sacc; a. meta- phase of third division in ascus, ■ :oSo;//. polar view of telophase <>f third division in ascu>, ing eight curved chromosomes, ■ 3 ioo. Fig. 74- Humaria rutilam . ol third division in ascus; alter Guilliermond. n6 DISCOMYCETES [CH. PEZIZACEAE: BIBLIOGRAPHY 1905 GuiLLlERMONn, A. Remarques sur le Karyokinese des Ascomycetes. Ann. Myc. iii, P- 343- 1905 Maire, R. Recherches cytologiques sur quelques Ascomycetes. Ann. Myc. iii, p. 123. 1906 Blackman, V. H. and FRASER, H. C. I. On the Sexuality and Development of the Ascocarp in Humaria granulata. Proc. Roy. Soc. B. 77, p. 354. 1907 Fraser, H. C. I. On the Sexuality and Development of the Ascocarp in Lachnea stercorea. Ann. Bot. xxi, p. 349. 1908 FRASER, H. C. I. Contributions to the Cytology of Humaria rutilans. Ann. Bot. xxii, p. 35 1908 Fraser, H. C. I. and Welsford, E. J. Further Contributions to the Cytology of the Ascomycetes. Ann. Bot. xxii, p. 465. 1909 Fraser, H. C. I. and Brooks, W. E. St J. Further Studies on the Cytology of the Ascus. Ann. Bot. xxiii, p. 537. 191 1 Brown, W. H. The Development of the Ascocarp in Lachnea scutellata. Bot. Gaz. Iii, p. 275. 191 1 GuiLLIEKMOND, A. Les Progres de la cytologic des Champignons. Prog. Rei Bot. vi, p. 389. 1913 Fraser (GWYNNE-VAUGHAN), H. C. I. The Development of the Ascocarp in Lachnea cretea. Ann. Bot. xxvii, p. 554. Ascobolaceae The large majority of the Ascobolaceae are coprophilous ; their ascocarp is soft and fleshy or somewhat gelatinous, and they possess a well-marked sheath which is closed during the early stages of development. They are distinguished from the Pezizaceae by the usually multiseriate arrangement of their spores, and by the fact that, when ripe, the asci stand well up above the hymenium before the spores are discharged. Often the asci are large and few in number ; the spores are brown or violet in Ascobolus, Saccoboltts and Boudiera, hyaline in the other genera ; they are usually ellipsoid, but round in Boudiera and Citbonia ; in Saccobolus they are enclosed in a special membrane within the ascus and are ejected together; and in Thelebolus and Rhyparobus they are sixteen or more in number. In most of the species investigated there is a conspicuous multicellular coiled archicarp, the central part of which gives rise to ascogenous hyphae. Some of the species also produce conidia (Ascobolus carbonarius), or chlamy- dospores (Ascobolus furfuraceus (Welsford), Asco- phanus carneus). Ascobolus furfuraceus is one of the commonest dung species, the ascocarp is green or brown in ,^J:^4:t^ colour with a characteristic scurfy margin. The after Dodge. archicarp (fig. 75) consists of sometimes as man)- IV] PEZIZALES 117 as twenty (Dodge), sometimes a much smaller number of cells. These arc at first uninucleate (Harper, Welsford), or multinucleate (Dangeard); later they always contain numerous nuclei (fig. 76 a). One of them, usually the Fig. 76. Ascobolus furfuraeeus Pers.; a. young archicarp, X750; b. rather older specimen showing pores between the cells, x 625 ; after Welsford. fi iurth from the apex (Welsford), enlarges, buds out ascogenous hyphae and functions as the oogonium. Those near the base form a stalk, and those towards the apex may be regarded as constituting a now functionless trichogyne. The cells on each side of the oogonium communicate with it by means of pores (fig. j6 b). Additional nuclei pass into it from both the stalk and terminal cells, and Welsford has observed their fusion in pairs in the oogonium. The fusion nuclei pass into the ascogenous hyphae. The asci are large and produce each eight spores which are violet or brownish in colour; the epispore is characteristically sculptured at maturity. There are eight chromosomes in the first division in the ascus, and four in the second and third (Dangeard (fig. 13), Fraser and Brooks). In Ascobolus glaber the archicarp is larger and more twisted than in A. furfuraeeus, and consists of some twenty or thirty cells from one or more of which the ascogenous hyphae develop I 1 tatigeard). In Ascobolus Winteri, a form occur- ring on goose dung, and apparently limited to this habitat, the archicarp (fig. jj), as described by Dodge, con- sists of three parts, a stalk of two or three cells, a series of larger, central cells, which give rise to the ascogenous hyphae, and a terminal row of three I'ig. 77. Ascobolus Winteri Rehm.; archi- carp, x 10S0 ; after Dodge. n8 DISCOMYCETES [CH. Fig. 78. Ascobolus immersus Pers. : archicarps showing paired nuclei, x 1000; after Kamlow. or four cells, which diminish gradually in diameter and which he terms a trichogyne. In Ascobolus immersus the mycelium consists of multinucleate cells, the archicarp is larger than that of A. Winteri and contains some twenty divisions, it is otherwise very similar. The cells contain numerous large nuclei and pores develop between them ; the ascogenous hyphae arise from a single cell. Ramlow observed nuclear fusions in the central cell of the archicarp, but referred them to bad fixation. His explanation may be adequate here, but it does not invalidate the observations of authors who have recorded fusions in properly fixed ma- terial. In archicarps which he held to be satisfactorily fixed Ramlow saw pairing of nuclei in the ascogenous cell, and records that they wandered in pairs into the ascogenous hy- phae (fig. 78), not fusing till the asci were about to develop. In the divisions of the ascus the number of chromosomes is stated by Ramlow to be sixteen through- out, but he does not figure the essential third anaphase. Ascobolus ccuiwnarius occurs on burnt ground among charcoal. The ascocarp is scurfy (furfuraceous), and greenish, or later brownish in colour. Numerous conidia are formed on the mycelium, and, according to Dodge, it is from a conidium, germinating while still attached to its stalk, that the archicarp is produced. It consists of a multicellular stalk, a fertile portion which contains twenty to fort)' cells arranged in a loose irregular spiral, and a terminal trichogyne more or less coiled, tapering towards the end, and including some ten to twenty cells. The apex of this trichogyne is found to wrap itself tightly round a second conidium, attached, like the first, to its stalk (fig. 79). This conidium is re- garded by Dodge as the an- theridium, but no cytological details have as yet been published. Ascophanus amicus is a somewhat variable species. .Its red, pink, or Fig. 79. Ascobolus carbonarius Karst.; archicarp, X280; after Dodge. IV] PKZIXALKS ti9 orange apothecia occur on the clung of cows and rabbits, on old leather, rope and similar habitats. Chlamydospores arc sometimes produced. As in Ascobolus, the archicarp is a coiled, multicellular filament; it varies considerably both in the size and number of its cells and in the amount of twisting which it undergoes. The central oogonial region includes three to seven large cells with granular contents. Between this and the parent hypha is a stalk of variable length and beyond it is a terminal portion (or trichogyne) of not more than seven cells which are narrower than the rest and appear to degenerate early (Cutting). The cells come into communication with one another by large pores (fig. 8ia), and Cutting has shown that nuclear fusions (fig. Si £) take place in all the cells of the oogonial region, and that all of them give rise to ascogenous hyphae. Ramlow also saw nuclear fusions in these cells, but heexplained them, as in Ascobolus immersus, as due to bad fixation. He also saw and figured exceptionally large nuclei, which had apparently become swollen, and were about to degene- rate. For him the normal process is the association of nuclei in pairs (fig. 80) without fusion, and their passage, still associated, into the ascogenous hyphae; here walls are Fig. 80. Ascophanus carneus Pers.; eld archicarp, showing associated nuclei, > Soo; alter Ramlow. formed so that the hypha consists of a series of binucleate cells. These tig. Si. Ascophanus carneiis Pers.'; a. section through young asci (ring nuclear fusion in two cells of the archicarp, =so : '. two cells of an archicarp, showing nuclear fusions, x 1240; after Cutting. nuclei, when satisfactorily fixed, showed a well-marked centrosome. Ramlow was unable to see whether one or several cells of the archicarp 120 DISCOMYCETES [CH. gave rise to ascogenous hyphae ; an investigation sufficiently searching to determine this point might have led to the recognition of nuclear fusions in normal material. The ascospore has a single large nucleus, and gives rise to multi- nucleate germ-tubes in which Ramlow's figures show numerous nuclei in pairs (fig. 1 6). In Ascophanus ochraceus Dangeard describes eight to fifteen oogonia as taking part in the formation of a single fruit. These, it would appear, are all borne upon the same hypha ; they may arise from adjacent cells, and indeed sometimes open into one another, so that the whole series seems equivalent to the oogonial region of A. carneus. Each cell, however, is described as bearing a twisted, multicellular trichogyne, which would indicate that each is an independent organ. Large ascogenous hyphae arise from the several " oogonia," and the view suggests itself that the so-called trichogyne may be in fact a premature ascogenous hypha. It is, at least, difficult to distinguish the one from the other in Dangeard's figures, and the species certainly requires further investigation. Saccobolus violascens is a violet or greyish violet species about I mm. in diameter. The archicarp is a coiled structure and is divided into only three or four cells (Dangeard), the central of which gives rise to ascogenous hyphae, while vegetative filaments grow up from the stalk and neighbouring mycelium (fig. 82). Fig. 82. Saccobolus violascens Boud.; archicarp ; after Dangeard. fig- 83. Thelebolus stercorals Tde. ; ascocarp with single ascus, x 250 ; after Brefeld. The species of Rhyparobius and Thelebolus, the two genera with many- spored asci, are all minute, coprophilous forms. They are distinguished by the fact that Rliyparobius produces several large asci, and Thelebolus only one (fig. 83). In both genera the cells of the mycelium are uninucleate. In Rhyparobius {Thecotheus) Pelletieri Overton has described several IV] PEZIZALES l 2 I multicellular archicarps, each rather like the single scolecite of Ascobolus. The cells are not connected by pores, and ascogenous hyphae arise from several in each archicarp. In R.brunneus Dangeard reports a single archicarp, consisting of a short, somewhat twisted branch. Ramlow has also recorded a single archicarp in A', polysporus and Barker in an unnamed species. Overton has made some study of tin- development of the numerous spores in A'. Pelletieri. The ascus nucleus divides as usual to form eight free nuclei, these undergo a period of rest and growth and then divide further till thirty-two free nuclei are formed. .Around these the spores are delimited in the usual way. Thelebolus stercoreus has a mycelium of uninucleate cells, from one of which the archicarp arises as a thick branch containing a single nucleus. Later two, four, and finally eight, are seen (fig. 85), and then septation takes My. S4. Thelebolus stercorals Tde. ; a. young ascocarp with binucleate asci ; b. ascus containing fusion nucleus, both x8io; after Ramlow. place, so that a row of cells is formed. Most of these are uninucleate, but one contains two nuclei (fig. 84*2); it enlarges and becomes the single ascus; in it the two nuclei fuse (fig. 84^). The definitive nucleus divides karyo- kinetically, sometimes as many as ten times, so that 1042 nuclei are formed. Fig. 8= Thelebolus stercorals, Tde.; development of archicarp. 17=0; after. Ramlow. Spore-formation takes place apparently in the usual way. The wall of the ripe ascus is about 2/x thick, but a thinner region is present at the apex, so that a concave papilla is differentiated, which is concerned in the dehiscence of the ascus. A sheath 1 if vegetative hyphae grows up from the surrounding cells. 122 DISCOMYCETES [ch. In Tkeleboliis Zukalii the origin of the ascocarp has been observed from a pair of intertwined hyphae (Ramlow, 1 9 14), but the cytology and further development have not yet been described. The closest analogy to the development of the ascocarp in Thelebolus is perhaps to be found in Sphaerotheca among the Erysiphales. In both we have a hypha which is at first uninucleate, later multinucleate. In both it divides to form a row of cells most of which enclose one nucleus. In both a single binucleate cell, typically penultimate, gives rise to the single ascus in which nuclear fusion takes place. But in Sphaerotheca the original uninucleate structure is the fertilized oogonium, while in Thelebo/ns stercorals an anthe- ridium has not been demonstrated. It remains to be seen what light the investigation of T/i. Zukalii will throw on these homologies. In view of the direct transformation of one cell of the row into an ascus, it becomes unjustifiable to correlate the septate structure here with the young archicarp of the Ascoboli or Ascophani. ASCOBOLACEAE: BIBLIOGRAPHY 1896 Harper, R. A. Ueber das Verhalten der Kerne bei der Fruchtentwickelung einiger Asconiyceten. Jahr. fiir wiss. Bot. xxix, p. 655 1903. 4 BARKER, P. T. B. The Development of the Ascocarp in Rhyparobius. Rept. Brit. Assoc. Southport and Cambridge. 1906 Overton, J. B. The Morphology of the Ascocarp and Spore-formation in the many spored Ascus of Thecotheus Pelletieri. Bot. Gaz. lxii, p. 450. 1906 Ram low, G. Zur Entwickelungsgeschichte von Thelebolus stercorals. Bot. Zeit. lxiv, p. 85. 1907 Dangeard, P. Recherches sur le developpement du perithece chez les Ascomy- cetes. Le Botaniste, x, p. 304. 1907 WELSFORD, E. J. Fertilization in Ascobolus furfuraceus. New Phyt. vi, p. 156. 1909 Cutting, E. M. On the Sexuality and Development of the Ascocarp in Ascophanus carneus. Ann. Bot. xxiii, p. 399. 1909 FRASER, H. C. I. and BROOKS, W. E. St J. Furthur Studies on the Cytology of the Ascus. Ann Bot. xxiii, p. 537. 1912 DODGE, B. O. Methods of Culture and the Morphology of the Archicarp in certain Species of the Ascobolaceae. Bull. Torrey Bot. Club, xxx, p. 139. 1914 Ramlow, G. Beitrage zur Entwickelungsgeschichte der Ascoboleen. Myc. Cen- tralbl. v, p. 177. Helotiaceae and Mollisiaceae The Helotiaceae and Mollisiaceae are distinguished from the Pezizaceae by the fact that their peridium differs more or less definitely in structure from the hypothecium. In Helotiaceae the peridium is prosenchymatous, composed of elongated parallel hyphae, usually light in colour and thin- walled. In the Mollisiaceae it is parenchymatous, of round or polygonal cells usually thick-walled and dark-coloured. In both families the ascus opens by the ejection of a plug, and not, as in most Discomycetes, by a lid. iv] PEZIZALES 123 The apothecia of the majority of forms included in these two families are small, often stalked, sometimes attached to a sclerotium ; they are waxy in consistency and may be glabrous or hairy. Must are saprophytes, often occurring on dead plants, some are parasitic. In Helotiaceae they are almost always sunk in the substratum (immersed), and in Mollisiaceae frequently superficial. Among the Mollisiaceae Pseudopezisa Trifolii is parasitic and causes the leaf-spot disease of clover. The leaves become increasingly spotted and die, so that the crop is often seriously injured. In this case the ascocarps are sessile and distinctly erumpent, developing within the tissue of the leaf, and breaking through the epidermis at maturity. There are several other species of Pseudopeziza, most on dead stems and leaves, a few on the living tissues of wild plants. The species of Tapesia occur on wood, branches, and dead leaves. The ascocarps are stipitate and pilose or downy, they are found in groups seated on a spreading weft of branched interwoven hyphae, by means of which the genus is readily distinguished. T. fusca is to be found on fallen twigs of larch and other plants. Among the Heliotiaceae the genus Helotium includes a number of species found on dead leaves, stems, beechmast, and similar habitats; these fungi are light-coloured, waxy and frequently stipitate. Another large genus, Dasyscypha, has a sessile or short-stalked ascocarp, thin and delicate in texture, and externally pilose; the species are sapro- phytic or parasitic. Dasyscypha Willkommii is the cause of a serious disease, the well-known Larch Canker. The apothecia are externally yellow with an orange disc. The ascospores give rise to germ-tubes which are unable to penetrate the bark, but obtain entrance through wounds caused by hail, ice or snow, or by the destruction of the needles by insects. The Larch moth (Coleophora laxicelld), for instance, is known to cause less injury in mountainous than in lower regions, and the fungal disease is propor- tionately less prevalent in the mountains. The mycelium ramifies chiefly through the soft bast, but may penetrate the wood as far as the pith. It spreads only in the autumn and winter, never in summer when the growth of the host is active. Where it spreads into the bark the tissues turn brown and shrivel, causing depressed canker spots in which yellowish white stromata are produced. These give rise to minute unicellular conidia, and later, if the atmosphere is sufficiently moist, to ascocarps. In the genus Sclerotinia the stalked ascocarps arise from sclerotia (fig. 81 i I. A number of species arc parasitic : S. tuberosa on - Xnemone nodosa; S. sclero- tiorum on the potato, cabbage and other hosts in the stems of which the sclerotia are formed; S.fructigena and .V. entered on species of Prunus and Pyrus where they give rise to brown rot, blossom wilt and other pathological conditions; ,s'. bulborum on hyacinth and other bulbs, and various species on I24 DISCOMYCETES [CH. members of the Vaccinieae, where the sclerotia are formed on the fruits. In 5. Vaccitiii the conidia are produced in chains and are separated by small cellulose disjunctors. They have a characteristic smell of almonds and are carried to the flower by insects, and probably also by wind ; they germinate to form septate hyphae which enter and fill the ovary. The Fig. 86. Sclerotinia tuberosa (Hedw.) Fuck.; sclerotia and apothecia, nat. size. mummified berries fall prematurely, lie during winter on the earth, and in spring give rise to the goblet shaped apothecia. In other species the conidia are borne on a conidiophore and belong to the form-genus Botrytis; the conidial phase on Primus and Pyrus is known as Monilia. The ascospores are unicellular and hyaline and often of unequal size. Celidiaceae, Patellariaccac, and Cenangiaceae In the previously described families the consistency of the ascocarp is either fleshy or waxy. In the following three, Celidiaceae, Patellariaceae, and Cenangiaceae, it is leathery, horny, or cartilaginous, and the ends of the paraphyses are interwoven to form a layer above the asci known as the epithecium. The hypothecium is well developed, the ascospores are some- times more than eight in number and are one to many-celled; in some species pycnidia are present. The three families are sometimes grouped together as Dermateaceae. iv] PEZIZALES 125 Some of the Celidiaceae occur on wood or bark, but the majority are parasitic on the thalli or apothecia of lichens, their hyphae ramify among the living tissues oi the host, and they were at first believed to be themselves lichen species. They are, however, without a thallus, and so without an algal constituent, and the host plant is clearly distinguished by its own fructification developed in the absence of the parasite. The fruits of Celidium variant, for example, form black points on the apothecia, or rarely on the thallus of the lichen Lecanora glaucoma. In this family the peridium is absent or but little developed. The I'atellariaceae are for the most part saprophytic, but include also a number of lichen parasites. These are erumpent, but the saprophytic forms are superficial, and are thus differentiated from the Cenangiaceae. They are distinguished from the Celidiaceae by the well-marked peridium of small, dark-coloured cells. The fruits are closed at first and either become flattened out as they develop, or open by a narrow or a star-shaped slit. In the Cenangiaceae the ascocarps are erumpent, sometimes developed on a stroma. They are dark-coloured, with a tough or somewhat gelatinous sheath, and, when mature, are cup or pitcher shaped; pyenidia or spermo- gonia are present in some genera. Bulgaria polymorplia, one of the best known species, occurs on dead trunks of trees, particularly beech. The cup is 1 to 4 cm. across, and is externally umber brown. The hymenium is black and shining and level or almost level with the top of the cup. The ascocarps burst through the bark as small, rust}' brown, scurfy knobs, which gradually expand at the apex. The substance is soft and tough, resembling india-rubber in consistency and appearance. The species is readily distinguished by its four, slightly curved, brown ascospores. It is stated to be a dangerous enemy of the oak, but details of its parasitism are not known. The genus Coryne is placed by many systematists in the neighbour- hood of Bulgaria. C. sarcoides is a common species on rotten trunks and stumps. The apothecia are crowded and dull red or purple in colour. Amongst them, or often occurring alone, are the conidial fructifications, rather paler in colour. Minute conidia are abstricted from the ends of the fertile hyphae. The ascospores are septate. Cyttariaceae The very curious family Cyttariaceae contains only one genus, Cyttaria. Six species are known, occurring in New Zealand, Tasmania, and South America ; all are parasitic upon species of Nothojagus. ( . Darwinii occurs very commonly in Tierra del Fuego, where it was collected by Darwin in 1.S33. 126 DISCOMYCETES [CH. "In the beech forests," he says, "the trees are much diseased; on the rough excrescences grow vast numbers of yellow balls. They are of the colour of the yolk of an egg, and vary in size from that of a bullet to that of a small apple ; in shape they are globular, but a little produced towards the point of attachment. They grow both on the branches and stems in groups. When young they contain much fluid and are quite tasteless, but in their older and altered state they form a very essential article of food for the Fuegian. The boys collect them and they are eaten uncooked with fish." He observed that they were smooth when young, "the external surface marked with white spaces as of a membrane covering a cell"; later the whole surface is "honeycombed by regular cells." These are the separate apothecia, considerable numbers of which occur on the same stroma. Bertero, at about the same time, recorded that the Chilian species (C. Bcrteroi) threw Fig. 87. Cyttaria Giinnii, Berk.; a. twig of Nothofagus Cunninghami with knobs bearing the fungus, x § ; b. group of stromata ; c. single stroma cut across ; all after Berkeley. iv] HELVELLALES 127 "out <>f these cavities an impalpable powder when it was touched, exactly as is observed in the Peziza vesiculosa" In all species the stromata seem to grow from a distinct disc (fig. 87), formed from the bark or the baric and wood of the host, and traversed in all directions by the mycelium, which doubtless gives rise to a fresh crop each season. The asci are rather short ami cylindrical and contain eight OVi 'id spores. In C. Darwinii Berkeley observed that the lower part of the troma was granulated as if beset with a small, black, parasitic Sphaeria; Fischer inter- preted these structures as spermogonia or pyenidia, and was able to observe them on different parts of the stroma of C. Hookeri and C. Harioti. He also noted, below the developing apothecia of C. Dancinii, certain stout, coiled, branching hyphae, which were at this stage almost without contents. Their appearance suggests that they are ascogenous hyphae, but Fischer made the alternative suggestion that they might be archicarps. In view of the presence of putative spermatia he made some search for trichogynes reaching to the surface of the stroma, but could find none, nor anyevidence of a sexual process. The Cyttariaceae have been compared to those members of the Cenan- giaceae in which the apothecia arise from a common stroma, and in which pyenidia or spermogonia are also present. In man_\- directions they require further investigation. CYTTARIACEAE : BIBLIOGRAPHY 1842 BERKELEY, M. J. On an edible Fungus from Tierra del Fuego and an allied Chilian Species. Trans. Linn. Soc. Lond. xix, p. yj. 1847 BERKELEY, M. J. Fungi. Hooker's Flora Antarctica, ii, p. 453. 1848 ISi kkll.KY, M. J. Decades of Fungi. Lond. Journ. Rot. 2nd series, vii, p. 576. 1885 Buchanan, J. On Cyttaria Purdiei. Trans. New Zealand Inst, xviii, p. 317. FISCHER, E. Zur Kenntniss der Pilzgattung Cyttaria. Hot. Zeit. xlvi, p. S12. HELVELLALES The members of the Helvellales are saprophytes, growing chiefly on the ground, sometimes on decayed wood and branches. Most are large, fleshy and stipitate. The hymenium is spread over the upper surface, and, in the few forms studied, is covered at first by a veil or membrane through which the paraphyses break, much as in the Pezizas, and which may behomologi/.cd with their peridium. There arc three families : Ascophore flattened, not stalked RH1ZIK VCEAE. Ascophore stalked fertile region of head distinct from stalk, ascus opening by a lid Helvellaceae. fertile region not always distinct from stalk, ascus opening by a plug 1 1 IGLOSSACEAE. I2t DISCOMYCETES [CH. Rhizinaceae The Rhizinaceae are characterized by their unstalked fructification, and include the genera Rhizina and Sphaerosoma. Rhizina has a flattened, crust-like ascophore, more or less concave below, and attached to the soil by root-like strands of mycelium. The asci cover the upper surface. Rhizina inflata occurs in this country only as a saprophyte, growing on soil, but in both France and Germany it has been found to attack conifers. The disease, known as ring disease, or root fungus, extends from a centre, infecting one plant after another and causing them to lose their needles and die. The mycelium ramifies in the intercellular spaces of the cortex, and within as well as between the cells of the bast, so that the sieve-tubes are completely filled. It forms also masses of pseudoparenchyma between the dead and diseased tissues of the host. The development of the ascocarp has been studied in R. undnlata where Fitzpatrick found a long, multicellular archicarp recalling that of some of the Ascobolaceae. He regards the terminal cell or cells as a trichogyne but there is no evidence that normal fertilization ever takes place or that male organs are ever developed. In due course, the central cells become continuous through large pores, and give rise to ascogenous hyphae into which the nuclei pass. Fitzpatrick observed paired nuclei in the oogonial region and in the ascogenous hyphae, and infers that nuclear association occurs in the archicarp, but that there is only one fusion, that in the ascus. Fig. 88. Sphaerosoma Jancsewskianum Roup.; apothecium showing oogonial cell, x 70 ; after Rouppert. [V] HELVELLALES 129 In Sphaerosoma the ascophore is more or less sunk in the substratum, and is attached by rooting hyphae which arc sometimes grouped on a short pedicel. y^^^^\. It is concave when young, but later forms /('^^V^/^sJ-'^irNv an irregularly globose mass over the upper ^-T^^^HiwlVl^JV^K surface of which the hymenium is spread fe*; ^^Kij^^V^^Wjft^^ (fig. 89). It resembles, in fact, a Peziza V. ^^^'^'^''^^^^7 which becomes very much reflcxecl at ^ .^^^^^L ^ In .S///. Janczewskianunt ( fig. 88 ), a large Fig. 89. Sphaerosoma fits, escem | Klotz.) oogonial cell has been recognized from Roup.; apothecium, x 6; after Roup- " pert. which the ascogenous hyphae originate, but no details of- its development are known. This genus has been variously placed in the Tuberaceae and Pezizaceae as well as in its present position. It shows resemblances to some of the former in its habitat under fallen leaves, and to the latter group in many points of general structure. RHIZINACEAE : BIBLIOGRAPHV 1909 ROUPPERT, C. Revision du genre Sphaerosoma. Bull. Acad. Sci. de Cracovie, p. 75. 1918 Fitzpai rick. H. M. Sexuality in Rhizina undulata Fries. Bot. Gaz. lxv, p. 201. Hclvellaceae The Helvellaceae are represented by five genera, Helvetia (fig. 90 <7), Morchella (fig. 90$), Verpa, Gyromitra, and Cidaris; of these the first four are British. In all a definite fertile head is distinguished from the sterile stalk, and over the more or less convoluted surface of the head the hymenium extends. Development has been studied only in species of Helvetia where the fruit arises as a tuft of branching, septate hyphae, and no archicarp has been observed. In //. elastiea, young ascophores, about 0'5 mm. in diameter, show no signs of fertile hyphae. A membrane of interwoven filaments encloses the whole fruit body, and below this a palisade of club-shaped hyphae is differ- entiated. As growth proceeds the membrane becomes broken, and the palisade increases in regularity, forming the boundary of the fructification except where, at the apex, the paraphyses are growing up. Later, as these increase in number, the ascogenous hyphae appear among them, and numerous asci are formed. In //. crispa the later stages of development are very similar to those in //. elastiea. Here nuclear fusions have been observed in the young G.-V. o 130 DISCOMYCETES [CH. ascogenous hyphae, replacing, as in Humaria rutilans, the obsolete sexual fusions, and preceding the fusions in the asci. Carruthers has studied the Fig. 90. a. Helvetia crispa (Scop.) Fr. ; />■ and c. Morchella vulgaris Pers.; after Boudier. nuclear divisions, and finds two chromosomes in the vegetative and four in the fertile hyphae. Four again appear in the first and second (meiotic) divisions in the ascus, after the second fusion has taken place, and two are recorded in the telophase of the third division, and in the mitosis in the spore. The ripe spore normally contains eight nuclei. In both species, after an ascus has arisen from the penultimate cell of a hvpha, the terminal cell may grow on, giving rise to others, and may fuse before doing so with the third cell of the hypha, which is the stalk-cell of the previously formed ascus. In Morchella esculenta the nuclear divisions of the ascus have been studied by Maire. After observing eight chromatin bodies in the prophase of the first division in the ascus, he found four in the prophase and anaphase of the third, and in the divisions of the spore nuclei ; this corresponds closely with Carruthers' results in Helvetia crispa. HELVELLACEAE : BIBLIOGRAPHY 1905 Maire, R. Recherches cytologiques surquelques Ascomycetes. Ann. Myc. iii. p. 123. 1910 McCubbin, W. A. Development of the Helvellinaceae. I. Helvetia elastica. Bot. Gaz. xlix, p. 195. 191 1 Carruthers, D. Contributions to the Cytology of Helvetia crispa. Ann. Bot. xxv, P- 243- IV] HELVELLALES LSI '/, oglossaceae The Geoglossaceae grow usually in damp or moist situations such as low, wet woods and shady slopes. They occur on soil or on dead branches or leaves, and two species of Mitrula are parasitic on living moss. The family includes some eight genera of which five are British. Fig. 91. a. Geoglossum hirsulum Pers., nat. size; b. Spathularia clavata Sacc, nat. size; c. Leolia lubrica Pers., form s/ipila/a,x^\ after Massee. The ascophore is erect and stipitate with the fertile portion terminal, and either club-shaped (fig. 91 n, b), laterally compressed, or forming a cup or a pileus (fig. 91 c). In some of the simpler forms, as in Geoglossum liirsnt/tm, there is no clear line of demarcation between the fertile and sterile regions. The ascus con- tains eight spores and opens by the ejection of a plug. The young ascocarp consists of a dense tangle of vegetative filaments; in the earl)' stages a more or less conspicuous veil has been identified in several genera (though not as yet in Gcogloss/tm). It is composed, as in the I lelvellaceae, of interwoven hyphae.derived from and continuous with the outer layer of the fruitbody. There are indications that it opens at first by a pore at the apex, but it soon breaks up into scales and dis- Fig. <)i. a. Geoglossum hirsulum Pers., x 230; /•■ appears. SpathulariaclavataS9.cc., X400; after Massee. 132 DISCOMYCETES [ch. In Lcotia lubrica a large branching cell, presumably an oogonium, occurs at the base of the very young ascocarp and appears to give rise to the ascogenous hyphae. As far as the characters of the mature fruit are concerned, two lines of development can be traced, both starting from Geoglossum and passing, the one through Spathularia to Vibrissea, the other through Mitrula and Leotia to the Helvellaceae. In the species of Spathularia and Vibrissea, as in Geoglossum, the spores are very long, narrow and septate, lying side by side in the ascus. Geo- glossum is distinguished by its coloured spores (fig. 92a), the other two genera, in both of which the spores are hyaline (fig. 92 b), by the form of the fructification. In the rest of the Geoglossaceae, as in the Helvellaceae, the spores are elliptical and hyaline, and are arranged one above the other in the ascus. The}' may be continuous or septate. In Mitrula the fertile region is irregularly club-shaped, and in Leotia pileate. A relationship to the Pezizales suggests itself at various points, and perhaps especially through Leotia, to the Helotiaceae and Mollisiaceae where, as in the Geoglossaceae, the ascus opens by a slit or pore from which a plug of wall substance is ejected, not as in the majority of the Helvellales and Pezizales by a definite lid. GEOGLOSSACEAE : BIBLIOGRAPHY 1897 MASSEE, C. A Monograph of the Geoglossaceae. Ann. Bot. xi, p. 225. 1908 DURAND, E. J. The Geoglossaceae of North America. Ann. ,\Iyc. vi, p. 387. 1910 Brown, W. H. The Development of the Ascocarp of Leotia. Bot. Gaz. 1, p. 443. Phacidiales In the Phacidiales the ascocarp is immersed in the matrix. It is usually small in size and leather}-, wax}-, or coriaceous in consistency; an epithecium is often developed. Certain members of the group resemble the Hysteriales in man}- points and differ from them chiefly in the greater exposure of the fertile disc at maturity. There are two chief families. Stictaceae The Stictaceae constitute a considerable group of small forms, occurring saprophytically on wood or other plant remains. Their development and minute anatomy, apart from systematic characters, is practically uninvesti- gated. They have a fleshy or waxy disc, pale and clear coloured, usually white, yellow, or tinged with pink. The sheath is not always developed, when present it is thin and white and is mealy owing to the presence of particles IV] 1'IIAC IDIALHS 133 of calcium oxalate; when the fruit opens it forms a white border around the hymenium. The pale colour, and the ragged or toothed dehiscence of the sheath are very characteristic. Phacidiaceae The Phacidiaceae are distinguished by their black, thick-walled apothecia, usually scattered, sometimes, as in Rhytisma, grouped on a black stroma. Where the fertile disc is circular the sheath splits in a stellate manner, but where it is elongated, dehiscence takes place by means of a slit running along its entire length. The species occur chiefly on dead herbaceous stems or leaves, but a few are parasitic. Rhytisma Acerinum (fig. 93) infects the leaves of various species of Acer (maple and sycamore). The mycelium ramifies in the living tissues of the Fig. (j,]. Rhytisma Acerinum (Pers.) Fr.; apothecium, x 160. host and causes yellow spots on the leaves about three weeks after infection. Some five weeks later pyenidia develop under the cuticle and produce small unicellular conidia. The epidermis and underlying tissues of the host become filled with hyphae and a dense, black sclerotium is completed. In this state the leaf falls and next spring the sclerotia thicken and become wrinkled: finally they burst by elongated fissures and expose the discs of the apothecia. The ascospores are filiform and septate; they are ejected with some force and reach the living leaves to which they are probably carried by the wind. Hysteriales lhi- Hysteriales are characterized by the black, elongated ascocarp, dehiscing by a longitudinal slit, so narrow that the disc is almost permanently concealed. [lie species are all minute; in some the disc is narrowly elliptical, in 134 DISCOMYCETES [CH. some it branches in a stellate manner, in others the ascocarp is raised and laterally compressed so as to resemble a miniature mussel or oyster shell standing on its hinge and with the opening uppermost. In this case, or when the ascocarp is superficial, it is rigid and carbonaceous in consistency, when developed beneath the epidermis of the host it is membranous. The ascospores are coloured or hyaline and are frequently septate ; the}' may be very long and narrow and may be surrounded by a gelatinous membrane. In a few cases pycnidia are known, producing oblong, unicellular, hyaline conidia. The majority of species are saprophytic on old wood, bark, or dry leaves. The mycelium is intercellular, and is sometimes parasitic on living plants though the apothecia reach maturity only on parts that have been killed. The details of cytology and development are not known, nor do these minute species, growing often on a hard substratum, seem very promising objects of study. The subdivisions of the Hysteriales, of which Hysteriaceae and Hypo- dermataceae are the chief, depend upon the consistency of the sheath, on the form of the ascocarp, and on whether it is superficial or immersed. Lophodermium Pinastri (Hypodermataceae) produces pine-blight or needle-cast in the seedling of Finns sylvestris and other conifers, causing them to drop their leaves. The mycelium ramifies in the leaf and gives rise first to pycnidia and later, usually after the leaf has fallen, to ascocarps. These are black and oblong, opening by a narrow slit. The spores are filif >rm and continuous. The disease does very considerable damage to young plants, often causing death. It attacks mature trees also and, though these are not themselves seriously injured, they act as centres of infection, particularly in the neighbourhood of seedbeds and nurseries. In the form of their fructification the Hysteriales are intermediate between the Discomycetes on the one hand, and the Pyrenomycetes on the other, and have been variously included under either of these headings. Their black, coriaceous ascocarps, opening by a narrow slit, differ from those of certain Phacidiales chiefly in the less exposure of the disc. They approach the Sphaeriales in the frequent occurrence of coloured, septate spores, as well as in the consistency and often in the form of the ascocarp, which is distinguished from a true perithecium chiefly by its elongated opening, and by the absence of periphyses1. Possibly a study of their minute anatomy may lead to more definite knowledge of their relationships. 1 For definition, see p. 140. IV] ti'i;kr.\i.ks 135 TUBERALES The Tuberales are typically subterranean though some species arc only imperfectly buried, or grow among decaying leaves. When mature the fruits emit a powerful odour by which rodents are apprised of their where- abouts. The ascocarp is eaten and the spores dispersed after passing through the alimentary canal of the animal. The ascocarp is more or less globose, sometimes completely closed, sometimes with a small opening. The hymenium may form a smooth lining t<> the fruit or may be thrown into elaborate folds so that the fertile region is divided into chambers. The asci contain one to eight spores, but. as far as is known, eight nuclei are always produced. The epispore is often elaborately ornamented at maturity. Early investigators classed the Tuberaceae with the hypogeal Gastero- mycetes, and a consequence of this survives in the use of the term gleba to describe the contents of the ascocarp, including both vegetative hyphae and hymenium. The Tuberales include a single family, the Tuberaceae; their relationship is probably to the Pezizaceae and Rhizinaceae. One or more series can be traced between these families and the truffles, the principal modifications being in the direction of adaptation to subterranean conditions by increased protection of the hymenium. This appears to have been achieved either by retaining the closed form of the young pezizaceous apothecium {Genea, Pachyphloeus) or by invagination of the fertile layer {Tuber) over a widely exposed surface such as is found in R/iiziua or Sphaerosoma. In either case room has been made for additional asci by throwing the hymenium into elaboratefolds. Massee, however, regards the globose asci and dark-coloured sculptured spores of Tuber as primitive, and derives from it Genea, and thence the Pezi- zales. Tuberaceae In Hydnocystis and Genea the ascocarp is fleshy or warted; it has a single aperture often more or less closed by project- ing hyphae. Internally the h\ menium may form a smooth F>g- 94-. <'■ Genea Klotzschii B. and Br.; ascus and para- ' . . . physis; b. Genea hispidula Yiit.; apotheciun lining, or, in Lrenea, is more Getiea sphaericaVilt..; apothecium; after Ma 136 DISCOMYCETES [CH. often divided into chambers, all of which communicate with the apical opening. The asci are cylindrical and contain eight uniseriate spores (fig. 94 a). The simplest species in fact resemble a nearly closed Peziza (fig. 94 b, c). In Stephensia and Pachyphloeus the hymenium is more elaborately con- voluted ; the asci in Pachypldoeus are stouter, and the spores irregularly biseriate. In Balsamia (figs. 95, 96) the asci are broadly oblong or subglobose; the mature ascocarp is completely closed and surrounded by a pseudoparen- chymatous sheath. The youngest ascocarps of B. platyspora which Fig. 95. Balsamia z'lilgaris Vitt.; after Tulasne. Fig. 96. Balsamia vulgaris Vitt. ; section through hvmenium ; after Tulasne. Fig. 97. Tuber rufum Pico ; general view of fertile region ; after Tulasne. IV] TUBERALKS 137 *, *v.. *•£&& Bucholtz was able to examine, showed a system of internal chambers lined by the hymenium and communi- cating at one or more points with the exterior. As development pro- ceeds these cavities increase in size and the hymenium becomes further convoluted, so that additional cham- bers are formed. In Tuber the ascocarp is ir- regularly globose, fleshy or some- times almost woody; internally the walls which divide the gleba are extensively branched, and the free space between them is diminished, so that the layers of the hymenium are brought close together and constitute the fertile "veins." Other "veins," white and sterile, run be- tween the hymenial layers and serve as air chambers (fig. 97). The asci are often globose, and the spores usually four in number, but the number varies, and is sometimes reduced to two or one (fig. 98). The development of the fruit has been studied by Bucholtz in Tuber rufum Pico; section through hymenium; after Tulasne. Tuber pubcrulum (fig. 99). The very young ascocarp consists of a mass of hyphae, the outer rather more loosely interwoven than the inner. Around the lower part a dense basal sheath is differentiated. Soon the first signs of the fertile veins appear as invagina- tions of the upper surface, and internally the loose tissue of the sterile veins 1 01 nes recognizable. Owing to the rapid growth of the upper portion of the young fruit, the basal sheath is bent backwards, while at various points along the fertile veins the first signs of asci appear. Later the peripheral tissues become thickened, together with the remains of the basal sheath, and form the peridium. This ultimately closes over the points where the fertile veins are in communication with the exterior. Thus the young fruit is open at first, the hymenium becomes internal by imagination and the peridium which covers the mature ascocarp is a secondary formation. The development of the fructification in Choiromyces maeandriformis approaches that of T. puberulum, but the basal sheath and peridium arc- less conspicuous. 133 DISCOMYCETES [CH. IV The ascocarps of many species of Tuber are edible, the most esteemed being T. tnelanosporum which does not occur in Britain. They grow chiefly ..am* ">^^ % P'ig. 99. Tuber puberulum (B. and Br.) Ed. Fisch. -e. development of ascocarp; a. x 52 ". am I 1. x 28; rf. and t.xii;/. section through mature ascocarp, x 6 ; all after Bucholtz. in soils consisting of sand mixed with clay and containing iron, or in mixed alluvium; the soil must be porous to secure sufficient aeration. Truffles occur in chestnut, oak, and especially beech woods and there is evidence that they form mycorhiza with the roots of these trees. The relation would appear to be of advantage to the fungus since the success of the culti- vation of edible truffles under oaks in France depends on keeping the roots near the surface. TUBERACEAE : BIBLIOGRAPHY 1903 BUCHOLTZ, F. Zur Morphologie und Systematik der Fungi hypogaei. Ann. Myc. i, p. 152. 1905 FAULL, J. H. Development of Ascus and Spore Formation in Ascomycetes. Proc. Boston Soc. Nat. Hist, xxxii, p. 77. 1906 BOULANGER, E. Notes sur la Trufife. Soc. Myc. xx-xxii, pp. 77 etc. 190S BfCHOLTZ, F. Zur Entwickelung der Choiromyces Fruchtkorper. Ann. Myc. vi, P- 539- 1909 MASSEE, G. The Structure and Affinities of British Tuberaceae. Ann. Bot. xxiii, p. 243. 1910 BUCHOLTZ, F. Zur EnnvickelungsgeschichtedesBalsamiaceen-Fruchtkorpersnebst Bemerkungen zur Verwandtschaft der Tuberineen. Ann. Myc. viii, p. 121. CHAPTER V I'YRKXOMYCKTES THE Pyrenomycetes include some 10,000 species; they are characterized by the fact that their ascocarp or perithecium is a more or less flask-shaped organ opening by a narrow pore, the ostiole, and containing a hymenium spread in a regular manner over the floor and lower part of the sides (fig. 100). It thus differs from the perithecium of the higher Plectascales where the asci are irregularly scat- tered, and from that of the Erysiphales where, except in the flattened perithecium of the Microthy riaceae, an ostiole is not developed. By some au- thors the term Pyrenomycetes is used to include all these groups and even certain other forms, such as the Tuberales. A study of the development of the truffles, however, has made clear their affinity with the Pezizales ; the mildews consti- tute a well defined and isolated group, distinguished, so far as tiny are known, by the form of their sexual organs ; and the higher l'lectascales differ from the present series and re- semble the simpler forms with which they have here been classified in the important character of the arrangement of their asci. There remain four groups, the Hypocreales, the Dothideales, the Sphaeriales, and the Laboulbeniales. The last are true Pyrenomycetes in the sense that they possess regularly arranged asci and a perithecium opening by an ostiole, but they are dis- tinguished by so man}- special characters that, though included under this heading, they can best be dealt with apart. 5»=, Fig. 100. Sordaria sp.; ascocarp in longitudinal section showing asci, paraphyses and periphyses, x 400. 140 PYRENOMYCETES [CH. The Hypocreales, Dothideales and Sphaeriales, have in common more or less pyriform or flask-shaped perithecia; these are sometimes isolated and free: sometimes sunk in the tissue of the host, and sometimes embedded in a stroma or cushion of fungal tissue. The perithecium is lined by delicate filaments, some of which, the periphyses, grow along and partially close the neck, and may protrude through the ostiole, while others (paraphyses) are mingled with the asci in the venter of the fruit. The neck of the peri- thecium varies very much in length, and is often markedly phototropic, the ostiole being directed towards the light, and thus incidentally towards a clear space so that, when the spores are shed, as wide a distribution as possible is ensured. So definite is this reaction in, for example, species of Sordaria, that if the direction of light be changed even- four or five days during development, a series of corresponding bends in the neck are produced. In Sordaria and its allies the asci elongate, reaching up to the ostiole and in turn discharging their spores; in species of Spumatoria and Chaetomium the asci deliquesce to form a mucilaginous mass which readily absorbs water and expands, being squeezed up the neck and exuded at the ostiole where it persists until dissolved by rain or dew. Accessory fructifications include chlamydospores and various types of conidia which may be borne separately on free conidiophores, or grouped together in pycnidia. In some cases there is evidence that the so-called pycnidia are spermogonia, and the spores they produce spermatia, but no case has been brought to light in which these still fulfil their function as fertilizing agents. A consideration of our rather scanty knowledge of the initiation of the perithecium in this group brings to light three main types of development. (i) In Chaetomium, in Sordaria (fig. 101) and its allies and in species of Hypomyces and Mclanospora there is a coiled archicarp of four or five cells; these are uninucleate in Hypomyces lateritus, Chaetomium spirale and Podospora hirsuta, multinucleate in Sordaria and Hypocopra and in other species of Chaetomium. In Sordaria macrospora the archicarp is straight instead of coiled and in S. fimiseda a swollen terminal cell has been reported. A pair of initial hvphae has been described in Rosellina querciua, but in no case has a sufficiently detailed study been made either to reveal nuclear fusions in the archicarp or to justify the inference that they do not occur. Under these circumstances it is possible to judge of the function of these initial filaments Fig. ioi. Sordaria fimicola Rob.: archicarps; after Dangeard. v] PYRENOMYCETES 141 only on the somewhat incomplete evidence that they give rise to ascogenous hyphae and on the basis of their resemblance to the sexual branches of other Ascomycetes. There is a very similar coiled hypha in certain species of Eurotium which is certainly a functional archicarp. Comparison may also be made with the female branch of Ascodestnis nigricans and with that of the Krysiphai eae. tin fhe second type of pyrenomycetous initial organ (fig. 102) may Fig. 10:. Polystigma rtibrumTiQ,.; mature archicarp, x Koo; after Blackmail and Welsford. Fig. 103. Xylaria polymorfha (Pers.) Crev. archicarp embedded in stroma, x 1000. readily be derived from the first. It occurs in forms where the perithecium is immersed either in the substratum or in a stroma, and its essential character is the prolongation of the tip of the archicarp to form a trichogyne-like 01 an. The appearance of this structure is associated with the development ofspermatia in spermogonia. Archicarps of the type in question are found in Polystigma among the Hypocreales and in Gnomonia, Poronia and Mycosphaerella among the Sphaeriales. In all these genera, however, the trichogyne appears to be merely vestigial; in Polystigma it never reaches the exterior of the host-leaf, in Gnomonia its connection with the coiled oogonial region is doubtful and in Mycosphaerella and Poronia it degenerates early. In Polystigma the ascogenous hyphae arise from vegetative cells and not from the archicarp and it is at least possible that the same is the case in the other genera named. A comparison is obvious between the archicarps of these forms and those of several Lichens and of such Discomycetes as I42 PYRENOMYCETES [ch. Lachnea cretea and the Ascoboli, where the coiled and septate archicarp is often still functional. A very common initial organ in forms with embedded perithecia is the short filament of cells sometimes known as Woronin's hypha (fig. 103). The cells are large and contain well-marked nuclei and lie in a nest of small- celled vegetative mycelium. Woronin's hypha has been found among the Hypocreales mNectria and among the Sphaeriales in Xylaria an&Hypoxylon ; it remains to be shown whether it still functions. It may have originated from the simple archi- carps of the Lower Pyrenomy- cetes or by reduction from forms with a multicellular trichogyne. With its final disappearance we reach such completely apogamous species as those of Cordyceps and Claviceps. (iii) A quite distinct type of primordium has been described in Strickeria, Sporormia and Pleo- spora; in these cases the asco- genous and vegetative filaments arise from a common initial cell which divides not only transverse- ly, but longitudinally, forming a Fig 10+. Strickeria sp.; initial cells of ascocarps; alter Nichols. compact tissue (fig. 104). Other hyphae may anastomose with this mass, or it may give rise alone to the whole fructification. Possibly some sugges- tion of its origin may be found in the peculiar, but apparently normally fertilized oogonium of Lcptosphaeria. The Pyrenomycetes do not appear to have given rise to any higher forms, and have themselves a greater vegetative development than any other Ascomycetes. They may be subdivided as follows : Wall of perithecium differentiated from stroma; perithecium wall and stroma, if present, soft in texture, either colourless or light coloured HYPOCREALES. perithecium wall and stroma, if present, firm, leathery or brittle, dark in colour Sphaf.RIALES. Perithecium always sunk in a stroma from the tissue of which its wall is not differentiated ; colour of stroma black or dark brown DOTHIDEALES. Minute, external parasites on insects, perithecium borne on a receptacle which also bears appendages; spores two-celled LABOULBENIALES v] HYPOCREALES 143 Hypocreales The I [>■[» >crcales are readily distinguished by the clear colour and more or less fleshy consistency of the perithecium or struma. In the majority of Pyrenomycetes the colour is black or dark brown, but here bright red, yellow, blue, and various paler shades are found, and it is only quite occasionally that so dark a tint as brown or dirt}- violet appears. The asci contain usually eight, sometimes four, and sometimes many spores. The spores are in most cases hyaline, but are dark-coloured in Melanospora and its allies: they are elliptical or filiform, and may be one or more celled. In a number of species conidia as well as ascospores are produced. The group includes both saprophytic and parasitic forms. There are some sixty genera of Hypocreales, and the group is subdivided primarily according to the development of the stroma. In the simplest forms the stroma is absent, and the separate perithecia may or may not be partly sunk in the substratum, in others a filamentous or a fleshy stroma appears, and the perithecia are more or less embedded. In the highest members the perithecia originate deep in the stroma, and remain immersed in it throughout their development. Upon these characters the subdivision of the group is based : Stroma absent, or, when present, with perithecia entirely superficial NECTRIACEAE. Struma forming a conspicuous matrix in which the peri- thecia are partially or entirely immersed HYPOCREACEAE. Nectriaceae The species of the genus Hypomyces are for the most part parasitic upon the pilei of various Hymenomycetes. H. aurantius occurs on old Polypori and on species of Stereum. Here the free perithecia are roughly oval in form, orange yellow in colour, and seated on a delicate filamentous stroma. The perithecium wall consists of an outer coat of narrow, closely woven hyphae, and an inner layer of larger, thinner-walled cells with scanty contents. The cavity becomes filled with paraphyses and developing asci, and is prolonged into the neck lined with short periphyses. The spores are two-celled and the wall at each end is usually prolonged into a point. Development has been studied by Moreau in Hypomyces lateritus, a form parasitic on pei ie of Lacterius, and placed by Maire in the genus Peckiella by reason of its unicellular spores. The cells of the vegetative mycelium are uninucleate, and the archicarp appears among them as a coil of uninucleate 144 PYRENOMYCETES [ch. cells; there is no sign of an antheridium. Nuclear division without wall- formation takes place in the archicarp so that each cell contains two or occasionally three nuclei. At a later stage, after abundant branching, the young perithecium contains a number of binucleate cells; from these the asci arise, the hypha bending over and cutting off a binucleate subterminal cell in the usual way. No fusion but that in the ascus was observed by Moreau. The chief interest of this life history lies in the origin of the bi- nucleate condition, as in some Basidiomycetes, by nuclear division. In Melanospora the stroma may be absent, but when present is charac- teristically fleshy; the perithecium neck is elongated; the species occur on the fructifications of the Pyrenomycetes, on those of Pezizaceae and Tuberaceae, on various plant remains and in one or two cases on living plants; thus M. damnosa may be a serious disease on wheat and rye. The development of M. parasitica was studied by Kihlman; this species is a parasite on certain fungi parasitic on insects, including Cordyceps militaris, which is itself a member of the Hypocreaceae. The first sign of the development of perithecia is the yellow coloration of the mycelium, which has hitherto been white. The archicarp is a stout, twisted, multicellular hypha forming two or more coils and ending in a somewhat pointed cell; its growth is renewed after the development of the sheath has begun and it divides into some fifteen cells; one of these, which may be termed the ascogenous cell, divides in three directions, forming a true tissue from which the asci arise. Mcla>iospora Zobe/ii1 is parasitic on various fungi and especially on the disc of certain Pezizaceae; Nichols found that the spores germinate to give rise to a mycelium in the cells of which the nuclei are arranged more or less in pairs2. The archicarp is a coiled or curved branch which becomes septate; near it a more slender antheridial hypha may develop, and, in some cases, may fuse with the female organ. Vegetative hyphae give rise to a sheath of the usual type with an outer layer, two or three cells thick, of thick-walled, isodiametric cells, and an inner layer of laterally compressed tubular cells; within this is a loose spongy parenchyma of cells rich in contents from which the asci arise. A connection between the archicarp and the asci has not been traced, but it seems probable that the whole central tissue of the perithecium may be derived from the divisions or branches of the archicarp perhaps, as in M . parasitica, by means of an ascogenous cell. A further study of the development of the perithecium and especially of the origin of the asci in this genus is much needed. The facts, especially in Jif. parasitica, suggest that the divisions of the archicarp after the develop- 1 Melanospora Zobelii (Corda) Fuckel = Ceratosloma brevirostre Fuckel. - Presumably owing to rapid division ; cf. p. 47, ante. v] HYPOCREALES H5 aunt of the sheath has begun, may correspond to the septation of the fertilized oogonium in other forms. Further, the origin of the asci from a single cell points to tin- Erysiphales and Laboulbeniales, and in view of the longitudinal divisions, perhaps especially to the latter. In Neciria the usually red or yellow perithecia are produced in groups on stromata of the same colour; the asci contain eight ascospores which are two- celled, and often produce conidia by budding while still in the ascus. The genus is large, including some 250 species among which .V. cinnabarina, the commonest in this country, is of very frequent occurrence on the living and dead branches of deciduous trees. The mycelium from the germinating spores is unable to penetrate the bark of the host, and infection takes place only through open wounds. Once established, however, the mycelium spreads rapidly especially in the xylem. The cambium and other tissues are not attacked but die as a result of the destruction of the wood, so that as develop- ment proceeds branch after branch is killed. Meanwhile the stromata appear (fig. 105); in the conidial stage they are bright pink and occur at all seasons Fig. 105. Neciria cinnabarina (Tde.) P'r. on a fallen twig; a. conidial stroma; /'. perithecia; x6; E. J. Welsford del. young on the dead and living branches; perithecia are produced only in the autumn and winter and only after the tissues have been killed; they are deep red in colour and are partly immersed in the deep red stromata. When a peri- thecium is about to be formed a coil of hyphae larger than the ordinary filaments of the stroma appears a little below the surface, and probably represents the remains of whatever sexual apparatus originally gave rise to the ascogenous hyphae. Neciria cinnabarina is thus one of the rather numerous fungi which pro- duce conidia during their parasitic phase, and ascospores only when the death of the host has rendered them saprophytic. In view of the life-history of this species it is obvious that there are two methods of checking the damage which it does; the burning of infected branches on which the development of the spores takes place, and the painting over of open wounds through which alone the entrance of the mycelium is effected. G. \ IO 146 PYRENOMYCETES [ch. NECTRIACEAE : BIBLIOGRAPHY 1882 Mayr, H. Ueber den Parasitismus von Nectria cinnabar'ina. Untersuchungen aus der forstbot. Institut zu Miinchen, iii, p. 1. 1885 Kihlman, O. Zur Entwickelungsoeschichte der Ascomyceten Melanospora para- sitica. Acta Soc. Sci. Fennicae, xiv, p. 313. 1896 NICHOLS, M. A. The Morphology and Development of certain Pyrenomycetous Fungi. Bot. Gaz. xxii, p. 301. 1909 Massee, G. On a New Genus of Ascomycetes {Gibsonid). Ann. Bot. xxiii, p. 335. 1909 Shaver, F. J. Notes on North American Hypocreales. Mycologia, i, p. 41. 1914 MOREAU, F. Sur le developpement du peVithece chez line Hypocreale le Peckiella laterita, (Fries) Maire, R. Bull. Soc. Bot. de France, Ixi, p. 160. Hypocrcaceae Polystigma is a small genus, the best-known member of which, P. rubrum develops on the leaves of Pntnus spinosa, of P. insititia and of the cultivated plum, where it produces conspicuous orange, yellow or scarlet stromata. Each of these is the result of a separate infection, and spreads over only a small part of the leaf, so that in autumn, when the leaves are shed, the host is freed from the disease. The fungus, however, hibernates in the fallen leaves, and next spring the ascospores mature, reach the young leaves and there germinate. Its development was first studied by Fisch in 1882, and by Frank in 1883, and these authors described trichogynes and the union of the latter with spermatia. More recent investigations, however, have shown that these organs, though present, are now no longer functional. The germinating ascospore gives rise to a mycelium which ramifies among the cells of the host and forces them apart; the hyphae become massed especially in the intercellular spaces below the stomata, and often push their way to the exterior between the guard cells. Finally the stroma may extend from the upper to the lower epidermis, and only a few isolated cells of the mesophyll remain in the infected region. The hyphae are multi- nucleate, they contain orange pigment and their originally thin walls are modified to form thick gelatinous membranes perforated by fine pits. The gelatinous walls are probabiy utilized as reserve material, for they are partly absorbed during the later stages of development after the fall of the leaf. During the summer, large flask-shaped spermogonia appear and open on the underside of the leaf, usually in the position of a stoma. The wall of the spermogonium consists of densely interwoven filaments and it is lined by thin, uninucleate spermatial hyphae (fig. 106). The mature spermatium is a filiform curved structure, narrowed at its free end; it contains a single, much elongated nucleus, staining homogeneously, and occupying the lower half or two-thirds of the cell. All attempts to bring about the germination v] HYPOCREALES ■47 of these spermatia have failed, and no relation of any kind has been de- monstrated between them and the female organ, consequently they must be inled as no longer functional, and their original use can be inferred only from their structure. Their small size, scanty contents, and large nucleus suggest that they are more appropriately constituted to act as fertilizing i i 11 1 s than as a means of vegetative propagation. The archicarp first appears as a multinucleate hypha, which becomes septate and somewhat elaborately coiled. The base can usually be traced to a vegetative filament; the apex ends freely in the mass of uninucleate mycelial cells (fig. 102); most of the cells of the archicarp contain several nuclei, but a few are uninucleate. The archicarps usually develop singly, generally below or near a stoma, through which vegetative filaments project (fig. 107). These projecting hyphae were regarded by Fisch and Frank as I i^. 106. PolysligmarubrumT}C;sftt- mogonium, ■ 250; after Blackmail and Welsford. Fig. 107. Polystigma rubrum IX'.; vege- tative hyphae projecting through stoma above archicarp, x 900 ; after Blackmail and Welsford. trichogynes, but Blackman and Welsford. and later Xienburg, failed to trace any connection between them and the coiled archicarps. On the contrary, the latter end blindly within the stroma with or without branching, and it i- only quite occasionally that they can even be traced upwards uds the stomata. Xienburg observed the formation of a pore between a multinucleate cell at the base of the archicarp and the large uninucleate cell next in order to it. At a later stage he found that the uninucleate cell had become binucleate, the nuclei being at first somewhat different in structure, and that certain large cells, which apparently developed from it. also contained i48 PYRENOMYCETES [CH. two nuclei each. In his opinion, the second nucleus in the originally uni- nucleate cell, is derived from its multinucleate neighbour, which he terms the antheridium ; the other binucleate cells receive their nuclei from it by conjugate division, and are the beginnings of ascogenous hyphae. Though he was unable to see either the entrance of the second nucleus, or the process of conjugate division, his facts are decidedly suggestive, but they point less to normal fertilization than to the pseudapogamous association of a vegetative and a female nucleus. The binucleate character of the later formed large cells may, as he suggests, be due to conjugate division, but, since he finds that the numerous binucleate cells in the sheath1 are the result of rapid growth, this character in the large cells is evidently susceptible of the same explanation. In any case the rest of the archicarp degenerates and owing to the refractory character of the material the ascogenous hyphae could not be further traced. According to Blackman and Welsford, all the cells of the archicarp degenerate without giving rise to ascogenous hyphae, and being functionless, retain their contents so that the)- can be recognized during the later stages of development as densely staining masses (fig. 108). The perithecia (fig. 109) arise in their neighbourhood, one in association with each archicarp, and the vegetative cells produce ascogenous hyphae, which become dis- tinguished by their large size, dense contents and well-marked nuclei. These Fig. 108. Polystigma rubriim DC; young perithe- cium; the ascogenous hyphae are not yet clearly distinguished, many of the nuclei are in pairs, the darkly stained remains of ihe archica'p are visible near the periphery; x68o; after Blackman and Welsford. Fig. 109. Polystigma rtibrutn DC ; matu thecium, x 270; after Blackman and W re pen- elsford. 1 Nienburg, p. 390, end of first paragraph. v] IIYI'Ot RKALKS 149 authors found some evidence that a first nuclear fusion takes place in the ascogenous hypha before the differentiation of the asci. The ascus is formed in the usual way from the penultimate cell of the hypha; the usual nuclear fusion and successive nuclear divisions take place during its development. In the genus Podocrea, the stroma is erect, and sometimes branched; in Hypocrea it is usually hemispherical or bolster-shaped and is colourless, or yellow or brown in colour. The majority of species occur saprophyticallv on wood, or as parasites on the larger fungi. In both genera and in their immediate allies, the spores are two or more celled. The systematic position of Podocrea alutacea} has undergone curious vicissitudes; in con- sideration of its form it was at first placed among the Basidiomycetes as Clavaria simplex, later it was regarded as a compound structure, the pyreno- mycetous fungus being held to be parasitic, according to different authors, on Clavaria ligit/a and on species of Spathularia. The stalk being thus attributed to another fungus, the ovoid perithecial portion was referred to the genus Hypocrea. The questi< >n was set at rest by Atkinson, who succeeded in growing the normal upright stroniata in pure culture from ascospores alone, and thus demonstrated that only one fungus was concerned. The species of Epichloe occur parasitically on grasses the stems of which become coated by the stromata. The stroma is at first white, then yellow; in the early stages of its development oval conidia are produced, later the peri- thecia, which are completely embedded in the stroma, reach maturity; the ascospores, like those of the remaining genera of the Hypocreaceae, are fili- form; Dangeard has shown that they are at first elliptical and uninucleate; later they elongate, the nucleus divides and the spore undergoes septation. The genus Cordyceps (fig. 110) includes about sixty species ; these are mainly tropical forms parasitic on insects, the bodies of which they transform into sclerotia from which the stromata grow out. The peculiar appearance of these structures has given rise to curious views as to their significance and medicinal value; thus Berkeley reports that Cordyceps sinensis is a "celebrated drug in the Chinese pharmacopoeia, but from its rarity only used by the Emperor's physician." The striking belief that it is "a herb in summer and a worm in winter," may perhaps sufficiently account for the esteem in which it was held. Tin' ascospores are multicellular and filiform and when shed break up into their separate cells. Germ-tubes from these, or from the conidia, infect the insect either as a caterpillar or chrysalis, and penetrating into its interior give rise to cylindrical conidia which enter the blood-stream and increase by \ east-like budding till the insect dies. A mycelium then appears and 1 Podocrea aluiacea I.imlau = Podostroma aliilaeciim (Pers.) Atkinson. ISO PYRENOMYCETES [CH. the formation of the sclerotium begins; chains of subaerial conidia may be produced on conidiophores arranged in a coremium or fascicle of parallel hyphae. This is the Isaria condition, and though there is little doubt that it is a stage in the development of the Cordyccps, the ultimate proof by culture has yet to be given. Fig. 1 10. a. Cord} nilitaris (I..) Link ; h. Cordyceps ophioglossoides (Ehrh.) Link; after Tulasne. The mature sclerotium is a compact mass of interwoven hyphae whose cells are rich in glycogen and oily matter. During its development the in- ternal organs of the host are completely destroyed and replaced by the mycelium, the skin alone remaining intact. From this mummified structure one or more stromata arise, emerging between two segments of the skin, usually near the head. The stroma is differentiated into an erect, sterile stem, which may be simple or branched, and a globose or elongated, fleshy, fertile portion, usually terminal on the stem and bearing the perithecia (fig. in). It is pale or bright coloured; red in the best known British species, C. tnilitaris ; and in other forms, purple, flesh-coloured, lemon-yellow or of various shades of brown. v] HYPOCREALES m As development proceeds the ovate or flask-shaped perithecia are dif- ferentiated ; they always arise deep in the stroma and may remain completely i >r partially immersed or may become superficial as they approach maturity. Where they are more or less free the surface of the head is usually rough, whereas when they are entirely immersed it is smooth, but in some cases the free perithecia stand so close together as to produce a smooth appearance. The cytological details of development have not been studied; the perithecia arise from the vegetative cells of the stroma and in no case 1m\ e any signs of sexual organs been seen; it would thus appear that Cordyceps is completely apo fa- mous. The first sign of the perithecium is the differentiation of a knot of deeply staining vegetative hyphae. The asci are long and slender with slightly swollen apices int< I which the spores Fig. 1 1 1. Cordyceps Barnesii Thwaites; , . ., perithecia, x 170; after Massee. do not penetrate; at maturity the contents of the apex swell and the wall is ruptured. The spores are arranged in a parallel manner, in a fascicle slightly twisted on its axis, and are nearly as long as the ascus; they are hyaline, very slender and almost always multicellular; they break up readily into their constituent cells which, as already stated, germinate separately to infect a new host. According to the investigations of Lewton-Brain several nuclear divisions take place in the ascus before spore-formation and the spores are multinucleate from their first inception. Two species, C. ophioglossoides (fig. iio<5>) and C. capitata, are parasitic on underground fungi of the genus Elaphomyces and do not produce true sclerotia; for these reasons they are sometimes separated as another genus Cordylia. The species of Claviceps, like those of Cordyceps, possess filiform a spores, and form sclerotia from which the stromata arise. The genus is, however, much smaller, including only six species parasitic on various Gramineae. Of these the best known is the almost cosmopolitan species C. purpurea, the ergot, on rye and other cultivated grasses. The ascospores germinate on the flowers of the host, and give rise to a mycelium which ramifies at first in the outer coats of the ovary and ultimately fills its whole cavity, forming a sclerotium. Outside the ovary, conidia are budded off, and at the same time a sweet fluid, the so-called honey-dew, is excreted ; it attracts insects which carry the conidia with 152 PYRENOMYCETES [CH. them to other flowers, where they at once germinate, and further infections are produced. On the completion of the conidial stage the sclerotia assume a firmer texture, and become dark purple or bluish black in colour. If they fall to the ground or are sown with the seed they give rise next spring to numerous stromata with violet stalks and reddish yellow heads. According to Fisch, the perithecia originate from two or three hyphal cells, which become filled with strongly refractive protoplasm and divide in all directions to form a roundish mass of cells distinguished from those of the rest of the stroma by their size and contents. As in Cordyceps, there is no trace of sexual organs. The perithecia are immersed in the stroma, and the asci produce filiform but continuous spores. The sclerotium is well supplied with reserve materials and contains certain poisonous substances including ergotic acid, a narcotic which diminishes reflex excitability ; sphacelic acid, the main cause of ergot poisoning, it gives rise to gangrene, and large doses produce tetanus of the uterus and cramp ; cornutin, an alkaloid causing contraction of the uterus. Thus the ergot sclerotia, if eaten with the grass by cattle, or included in the grain used for bread-making, are responsible for serious disease. When grain was less carefully purified than at present the inhabitants of whole districts sometimes became afflicted with gangrene, and the occurrence of the sclerotia in pastures is liable, owing to the presence of cornutin, to cause abortion in sheep or cows, so that many local traditions as to the prevalence of abortion in certain farms, or in certain byres, are probably traceable to this cause. Cornutin is of medicinal value, and the sclerotia are collected for this purpose. HVPOCREACEAE : BIBLIOGRAPHY 1843 BERKELEY, M. J. On some Entomogenous Sphaeriae. London Journal of Botany, ii, p. 205. 1882 Fisch, C. Beitrage zur Entwickelungsgeschichte einiger Ascomyceten. Bot. Zeit. xl, p. 850. 1883 Frank, E. Ueber einige neue oder wenige bekannte Pflanzen Krankheiten. Ber. der deutsch. bot. Ges. i, p. 761. 1895 Massee, G. A Revision of the Genus Cordyceps. Ann. Bot. ii, p. 207. 1901 Lewtox-Braix, L. Cordyceps ophioglossoides. Ann. Bot. xv, p. 522. 1905 ATKINSON, G. F. Life-history of Hypocrea alutacea. Bot. Gazette, xl, p. 401. 1907 DANGEARD, I'. A. Recherches sur le developpement du perithece chez les Ascomy- cetes. Le Botaniste, x, p. 352. 1912 Blackman, V. H. and Welsfokd, E. J. The Development of the Perithecium of Polystigma rubrum. Ann. Bot. xxvi, p. 761. 1114 NlENBERG, W. Zur Entwickelungsgeschichte von Polystigma rubra. Zeitschr. fur Bot. vi, p. 369. DOTHIDEALES The Dothideales constitute a small group of some four hundred species, included in twenty-four genera, forming a single family, the Dothideaceae. They are parasites or saprophytes on the leaves and stems of higher plants, v] SPHAERIALES 1 53 on which they produce stromata usually below the epidermis and finally exposed by its rupture. The stroma is externally black and hard, built up of hyphae closely interwoven to form a pseudoparenchyma ; internally it is of much looser consistency, and is often white or brownish in colour. The perithecia are without definite walls, so that the asci develop in mere cavities in the stroma, which however have the globose form of ordinary perithecia, and are bordered by cells rather smaller and narrower than those of the surrounding mycelium. In some cases, where the inner tissue of the stroma is very loosely interwoven, the perithecium is, however, definitely delimited. In Dothidea the stromata form black projecting cushions, which in D. virgultorum occur on the living, as well as the dead stems and branches of the birch. In Plowrightia the very similar stromata run together in masses. P. morbosa is a serious disease attacking species of Prunusi especially the cherry and plum. The mycelium penetrates the living branches which become swollen and deformed and on which stromata and finally perithecia are produced. SPHAERIALES The Sphaeriales are distinguished by the dark colour and membranous, corky or carbonaceous texture of their perithecia, and of their stromata when present. They number already considerably over six thousand species, and new species are constantly being brought to light, so that there is no doubt that a study of the tropical forms, at present very incompletely known, will greatly increase their number. Not only the number of species, but the number also of individuals is very considerable; the majority are saprophytes, and serve a useful purpose in bringing about the first stages of decay in such resistant materials as wood and straw. They greatly outnumber the Hypocreales and Dothideales, and it is from their black or brown colour and often charred appearance that the name Pyrenomycetes is derived. The origin of the group has been proposed through Chaetomium, which is sometimes without an ostiole, from the Krysiphales, or, in view of the structure of the sexual organs, from an Eurotium-like form among the Plectascales. Unfortunately their small size and resistant texture as well as the nature of their habitat make many of the simpler species unfavourable subjects of study, and our knowledge of their development is at present very fragmentary. Son/arid and some others can be grown on artificial media and satisfactory results may be anticipated from a further application of this method. Some of the larger forms with a well-developed stroma can readily be handled but in none of these has normal sexuality yet been observed. The perithecia in the simplest forms are borne singly, free or partially iS4 PYRENOMYCETES [ch. embedded in the substratum; from these may be traced a series of inter- mediate forms culminating in the elaborate stromata and sunken perithecia of the highest species. There is, in fact, a marked parallelism between the Sphaeriales and Hypocreales, and it is by no means clear that the colour and texture of the stroma and perithecium walls are of sufficient im- portance as criteria of relationship to justify their separation, nor is it indicated that the members of the families Nectriaceae or Hypocreaceae resemble one another more closely than the numerous Sphaeriales, though these are dispersed among a series of eighteen or nineteen families. The method of classification is however convenient, and considerably more knowledge will be required before a natural system of classification can be elaborated. In the meantime, the subdivisions of the Sphaeriales rest on the structure and development of the stroma, the form of the ostiole, and the colour and septation of the spores. As in the Hypocreales, various sorts of accessory fructifications are present. In the first eight families of the Sphaeriales the perithecia are more or less free, though they may be partly sunk in the substratum, or in a weft of hyphae, or may be seated on a definite stroma. In the remaining ten families the perithecia are immersed either in the substratum, or in a stroma which may reach considerable elaboration. The most important of the eighteen families of the Sphaeriales are: Perithecia free Peridium membranous ostiole beset with long hairs often elaborately coiled or branched Chaetomiackae. ostiole without long hairs; mainly coprophilous SoRDARIACEAE. Peridium leathery or carbonaceous short neck Sphaeriaceae. long, sometimes filiform neck Ckratostomatace.u;. Perithecia embedded in substratum Perithecia immersed, upper part free ostiole round Amphisphaeriaceai ostiole elliptical LOPHIOSTOMATACEAE. Perithecia completely immersed, ostiole only pro- jecting peridium membranous or leathery, neck short paraphyses absent MYCOSPHAERELLACEAE. paraphyses present Pleosporaceae. peridium leathery or carbonaceous, neck long GNOMONIACEAE. Perithecia embedded in stroma Stroma developed within substratum, differen- tiated from it VALSACEAE. Stroma free ascospores very small, sausage-shaped and hyaline or light brown, unicellular DlATRYPACEAE. ascospores unicellular, rarely bicellular, dark brown XYLARIACEAE. v] SI'IIAKRIALES 155 Chaetomiaceae The Chaetomiaceae occur on straw, paper, dung and other waste materials; they possess free, thin-walled perithecia beset with numerous characteristic, long hairs (fig. 112), which are often elaborately branched or coiled. On these, or on the ordinary vegetative mycelium, conidia are produced. An ostiole is lacking in ( '//. fitnete, presumably the most primitive member of the genus; in the remaining species it is present and the peri- thecium is of the typical sphaeriaceous form. In Chaetomium spirale the cells of the mycelium contain each a single nucleus, the archicarp arises as a coiled branch and divides into four or more uninucleate cells. There is no sign of an antheridium. Vegetative hyphae grow up from the stalk of the archicarp, and from the filament on which it is borne, and form a sheath, the outer cells of which are prolonged as hairs. Small pyriform conidia are abundant. Ch. Kunzeanum shows a very similar archicarp (fig. 1 13), but here the cells, as described by Vallory for the variety chloriiuim, each contain several nuclei which are often found approximated in pairs. This arrangement is reported to be as common in the vegetative mycelium as in the cells of the archicarp, and is doubtless a result of rapid division. I I \ \ Ficj. 112. Chaetomium pannosum Walk.; x ;o ; W. Page del. Fig. 113. Chaetomium Kunzeanum Zopf; arcliicarps ; after Oltmanns. i56 PYRENOMYCETES [CH. In due course the archicarp becomes surrounded by a sheath of vegetative hyphae within which its growth is continued so that a mass of cells is pro- duced from which asci at last arise. In the meantime the sheath becomes differentiated into an outer coat of relatively large, brown-walled hyphae, and an inner layer of smaller cells which become narrow and elongated. As development proceeds a cavity appears within the perithecium, usually just above the ascogenous cells, and branches from the lining mycelium grow out to form the periphyses; paraphyses are not produced (fig. 114). The ripe spores are shed into the cavity of the perithecium, and do not reach the exterior immediately on leav- ing the ascus. In addition to the above, two or three otherspecieshave been examined, and show the same type of archicarp and of perithecium, but in no case has any further cytological detail been worked out. The uninucleate species in particu- lar would probably repay investigation and special attention ought to be given to the septation of the archicarp and to the number of cells from which ascogenous hyphae originate. Fig. 114. Chaetomium Kunzeanum Zopf; perithecium, x 200 ; after Zopf. CHAETOMIACEAE : BIBLIOGRAPHY 1881 ZOPF, W. Zur Entwickelungsgeschichte der Ascomyceten. Chaetomium. Nova Acta Acad. C. Leop.-Carol. G. Nat. Cur. xlii, p. 199. 1887 Oltmanns, F. Ueberdie Entwickelung der Perithecien in der Gattung Chaetomium. Bot. Zeit. xlv, p. 193. 1907 Dangeard, P. A. Recherches sur le developpement du perithece chez les Ascomy- cetes. Le Botaniste, x, p. 329. 191 1 Yali.ory, J. Sur la formation du penthece dans le Chaetomium Kunzeanum Zopf. var. chlorinum Mich. Comptes Rendus, cliii, p. 1012. Sordariaceae The Sordariaceae are mainly coprophilous ; their perithecia are typically free, sometimes superficial, sometimes so deeply embedded in the substratum that little more than the neck protrudes from it. The genus Hypocopra is exceptional in possessing a small stroma in which the perithecium is immersed, but it resembles Sordaria in all other points. The present family differs from the Chaetomiaceae in bearing only short filaments instead of v] SPIIAKRIALES 157 long hairs around the ostiole, and from the Sphaeriaceae in the habitat and type "f spore. The mycelium is in most cases composed of multinucleate cells, but in Podospora hirsuta the cells are uninucleate (fig. 115), recalling the condition in several species of Chaetomium. The commonest type of archicarp is a stout, coiled, septate hypha which soon becomes surrounded by vegetative filaments; it is usually terminal, but is occasionally intercalary, for instance in Sordaria fimicola. Dangeard lias found a straight archicarp (fig. 1 l&) in Sordaria macrospora, and in [868, for S. fimiseda, Woronin described an archicarp with a swollen terminal cell recalling the oogonium of Ilmiuuia granulata. Fig. 115. Podospora hirsuta Dang. , archicarp; alter Dan- Fig. 116. Sordaria macrospora Auersw.; a. straight archicarp ; after geard. Dangeard. In Sporortnia intermedia the perithecium is initiated by the enlargement of a multinucleate mycelial cell which is often intercalary. It undergoes not only transverse but also longitudinal divisions, forming a pseudoparen- chymatous mass of uninucleate cells (fig. 1 17), with which various neighbouring cells anastomose. The mass thus formed is responsible for the whole contents of the perithecium, though the outer walls may be formed by ordinary vegetative hyphae. In view of this fact it seems doubtful whether the initial cell should here be regarded as an oogonium, that is to say as having at one time had a sexual significance, and not rather as a preliminary stage in tin: development of such a mass <>f hyphae as initiates the apogamous perithecium of Claviceps and its allies. In some of the Sordariaceae each I11;. 1 1;. Sporormia intermedia Auersw. ; initial spore is surrounded by a layer of cells of perithecium ; after Dangeard. i58 PYRENOMYCETES [CH. mucilage {Sordaria macrospora, S. fimicola, etc.), in others (fig. 2e) one or two appendages are produced (S. fimiseda, S. coprophila, Podospora anserina, etc.). These may be gelatinous and derived wholly or partly from the epi- plasm apparently much as the ordinary thickening of the spore wall is derived, or they may form part of the young spore. In the latter case they are at first rich in protoplasm, but later most of their contents pass into the middle portion of the spore, which becomes ovoid, and the appendage is cut off by a wall (S. globosd). Both types of appendage may occur on the same spore. They are sometimes hooked and they become twisted together and serve to attach the spores one to another. The uppermost appendage appears, in some cases at any rate, to become fastened to the tip of the ascus (S- Brefeldii. SORDARIACEAE : BIBLIOGRAPHY 1883 Zopf, YV. Zur Kenntniss der anatomischen Anpassung der Pilzefruchte an die Funktion der Sporentleerung. Zeitschr. fur Naturwiss. iv ; ii, p. 540. 1886 WORONIN, M. Sphaeria Lemaneae, Sordaria fimiseda, Sordaria coprophila und Arthrobotrys oligospora. Beit, zur Morph. und Phys. der Pilze, iii, p. 325. 1901 MASSEE, G., and SALMON, E. Researches on Coprophilous Fungi. Ann. Bot. xv, P- 315- 1907 DANGEARD, P. A. Recherches sur le developpement du perithcce chez les Ascomy- cetes. Le Botaniste, x, p. 333. 1912 WOLF, F. A. Spore Formation in Podospora anserina, (Rabh.J Wint. Ann. Myc. x, p. 60. Sphaeriaceae The perithecia of the Sphaeriaceae are superficial, and are borne singly or in groups; the peridium may be smooth or beset with hairs or spines. The papillate ostiole distinguishes this family from the succeeding forms with free perithecia. The majority are saprophytic on plant remains, frequently on wood; some are parasites, such as the species of Coleroa (fig. 118), which occur on the leaves of Potentilla, Rubtis, and other flowering plants. Rosellina quercina, the oak root fun- gus, attacks the roots of oak seedlings; the hyphae enter the living cells of the cortex and pith ; they are at first hyaline, later dark in colour, and become twisted together into strands, the so-called rhi- zoctonia; these attack the roots of neigh- bouring oak plants, wrap a weft of hyphae about them and enter their cells. The Fig. 118. Coleroa Potenlillae (rr.) Wint.; perithecia, x 192. fungus may form black, chambered scle- v] SPHAERIALES i59 rotia which originate in the cortex of the host root; reproduction is by means ot conidia formed in summer on the surface of the soil, and further by ascospores produced in perithecia, I [artig has found that the perithecium is initiated by the development of a pair of thick hyphae rich in contents. These become enclosed within a mass of vegetative tissue, but their subse- quent behaviour lias not been determined, and no details of development are known either here or in other members of the family. SPHAERIACEAE : BIBLIOGRAPHY • HARTIG, R. Der Eichenwurzeltodter Rosellina quercina. Untersuch. aus der forst- botanische Inst, zu Miinchen iii, p. 1. Ceratostomataceae The Ceratostomataceae resemble the Sphaeriaceae in most of their characters: they are distinguished by the elongated neck of the perithecium, which is often drawn out to form a delicate hair-like process. The method of liberation of the spores in this family presents an interesting problem, but neither that question nor the development of the perithecium has yet been elucidated. A mphisphaeriaceae In the Amphisphaeriaceae the young perithecium is sunk in the substra- tum; as it matures it becomes more or less free, though in contrast to the con- dition in the Sphaeriaceae and Ceratostomataceae, its base is always immersed. Development has been studied in a species of Teichospora and a species of Teichosporella, now both included under the genus Strickeria, charac- terized by its muriform spores. The spore produces numerous germ-tubes which give rise to a mycelium of multinucleate cells ; certain cells increase in size and be- come both transversely and longi- tudinally divided till a parenchy- matous mass is produced (fig. 1 19). Other vegetative hyphae may fi >rm a scanty investment, but often the perithecium develops without this addition. Asci appear as large uninu- cleate cells, and the tissue around them disorganizes. The outer hy- phae become hard and dark only when the perithecium approaches maturity Fig. 1 11;. Shi keria sp, ; initial cells of ascocarps : after Nichols. 160 PYRENOMYCETES [CH. The type of development here is very similar to that already described for Sporormia\ it seems very doubtful whether the initial cell of the peri- thecium should be regarded as an oogonium, or whether the development is purely vegetative. The peculiarity in either case is the formation of the bulk of the perithecium from a single cell instead of, as in the majority of forms, from a complex of interwoven hyphae differentiated into sexual and vegetative components. AMPHISPHAERIACEAE : BIBLIOGRAPHY 1896 Nichols, M. A. The Morphology and Development of certain Pyrenomycetous Fungi. Bot. Gaz. xxii, p. 301. Lophiostomataceae The perithecia of the Lophiostomataceae are borne singly; during de- velopment they are embedded in the substratum, and they may so remain or may become partially free at maturity. There is no stroma, and the peridium is black and brittle. So far there is a close resemblance to the Amphisphaeriaceae, but the Lophiostomataceae are distinguished by the form of the ostiole, which is very large and laterally compressed, so that in external appearance they approach certain of the Hysteriales which in many cases they further resemble in their habitat on vegetable remains such as wood and bark. None of the species has been investigated in detail. Mycosphaerellaceae The Mycosphaerellaceae are parasitic forms occurring usually on leaves and giving rise to various kinds of leaf-spot. The perithecia are sunk in the substratum and develop either under the cuticle or beneath the epidermis, breaking through at maturity. The ascospores are usually septate, frequently bicellular and sometimes dark-coloured; except in the transitional genus Stigma tea, paraphyses are not developed. In several cases the formation of the perithecia is preceded by a conidial stage. Mycosphaerella nigerristigma forms pyenidia on the living leaves of Primus pennsylvanica and perithecia after the leaves have fallen. A tri- chogyne like that of Polystigma has been recorded ; it degenerates, leaving a basal cell, but whether this functions is not known. MYCOSPHAERELLACEAE : BIBLIOGRAPHY HJI4 HiGGlNS, B. B. Life-History of a new species of Sphaerella. Myc. Centralbl. iv, p. .87. v] SPHAERIALES [61 Pleosporaceae The Pleosporaceae are saprophytes or in a few cases parasites, f'>r the most part on seed plants but in some cases on Pteridophyta, Bryophyta or Lichens. The perithecia are immersed in the substratum, the ostiole only projecting, but they may become more or less exposed by the rupture of the covering tissues. The peridium is leathery or membranous. The genus Pleospora includes some 225 species, several of which occur on grains and other grasses where they show biological specialization. Pleospora kerbarum is a facultative parasite on the leaves of angiosperms ; the perithecium is initiated by the division of a hypha into numerous short nils from which branches grow out. The central cells, and later the basal parts of the branches, divide in various directions till an irregular paren- chymatous mass is formed. By further growth and division the mass assumes a globular shape and the central cells become elongated and differ- entiated as paraphyses. Later, asci appear, developing from the same cells as the paraphyses and each produces eight muriform spores (fig. 120). Fig. 120. Pleospora sp .; germinating spores, x 1000. M ulticellular conidia also develop on branched hyphae, the terminal cells of which form the sterigmata. After the spore is shed the hypha may continue to grow, a new sterigma being formed above the old one. The name Macrospo- rium parasiticum was formerly applied to the conidial stage of this species. The genus Venturia includes over fifty species, several of which are para- sitic on living leaves; the perithecium is immersed and the large ostiole beset with stiff hairs or bristles. The species grouped under Fusicladium among the I lyphomycetes are in some cases conidial forms of this genus. The conidia are two-celled, borne on short conidiophores arranged in groups; /-. dendriticum is the cause of scab or black-spot on apples, and /■'. Pyrinum of a similar disease on pears. 1 1 l62 PYRENOMYCETES [CH. Leptospliaeria includes some 500 species characterized by the papillate or conical ostiole, usually free from hairs. The majority are saprophytes on plant remains, some are parasites on land plants, and some on the Red Algae. L. Lemaneae occurs on the thallus of various species of Lemanea (fig. 121). The mycelium consists of uninucleate cells and ramifies in the intercellular spaces of the host, sending branched haustoria into the cells. Here and there the hyphae are dilated (fig. 122 a, b\ and in these regions show denser and more refractive contents than usual. Fusion takes place between the dilated portions (fig. 122 r, d) which may be terminal or intercalary, and there is Fig. [21. Leptosphacria Lemaneae (Cohn) Brierley ; transverse section through thal- lus of Lemanea, showing perithecium, x 125 ; after Brierley. Fig. 122. Leptosphaeria Le- maneae (Cohn) Brierley; a. b. c. d. stages of fusion between dilated hyphae ; after Brierley. evidence that the nucleus of one of the swollen cells passes across into the other, which may therefore be termed the oogonium, and fuses with its nucleus. The oogonium then divides to form a number of multinucleate cells from which ascogenous hyphae arise. The nuclei in these hyphae are paired and the usual fusion takes place in the ascus. From the cells adjoining the oogonium the delicate hyphae of the sheath grow up. The morphology <>f the sexual organs in this genus is quite unusual, but they may perhaps best be compared with the dilated cell observed by Dangeard in the initiation of the perithecium in Sporormia intermedia; in that case, however, there does not appear to be a functional antheridium, and vegetative cells as well as ascogenous hyphae are stated to develop from the initial cell ; the resemblance demands further investigation. v] SPHAERIALES 163 The family is rich in conidial forms, and it is probable that several species ol Fungi tmperfecti, including the pyenidial genera Pkomaand Hendersonia and also Cercospora, a form with long septate conidia on free conidiophores are stages in the development of members of the Pleosporaceae. PLEOSPORACEAE: BIBLIOGRAPHY 6 Woronin, M. Sphaeria Lemaneae, Sordaria fimiseda, Sordaria coprophila, und Arthrobotrys oligospora. Beit, zur Morph. und Phys. der Pilze, iii, p. 325. 1 Miyabe Kingo. On the Life History of Macrosporium parasiticum, Thiim. Ann. Bot. iii, p. 1. i] ; Brii rley,W. B. The Structure and LifeHistoryof Leptosphaeria Letnaneae (Cohn). Mem. and Proc. Manchestei Lit. and Phil. Sue. Ivii, 2. p. 1. Gnomoniaceae The Gnomoniaceae are for the most part saprophytic on the leaves or 1 1 ther parts of plants. The perithecia are embedded in the substratum from which their long necks project. The ascus is characterized by a thickened apex through which a canal allows the exit of the spon-s. The spores are hyaline and paraphyses arc usually not developed. The family differs from the Pleosporaceae in the long neck of the perithecium and the thickened apex of the ascus. There is no stroma, and this fact, as well as the dark colour, distinguishes Gnontonia from the similar genus Polystigma among the Hypocreales. Gnomonia erythrostoma is the cause of an epidemic disease known as cherry-leaf-scorch, which attacks the foliage of Primus avium and of several varieties of the cultivated sweet cherry. The mycelium ramifies on the leaf and runs back to the base of the petiole, where it prevents the formation of the absciss layer. In consequence the infected leaves do not fall, but remain hanging on the branches; they are the only source of infection in the following summer, and their destruction is therefore a sure method of checking the disease. Infection usually takes place in June; towards the end of August spermo- gonia appear; they are shallower than those of Polystigma, but otherwise \ ery like them, with a wall of closely compacted hyphae and a small circular 1 1 1 ile opening on the under surface of the leaf. The spermatial hyphae are narrow and tapering, and their extremities are abstricted to form the sper- matia, each of which contains a long threadlike nucleus and a relatively small amount of cytoplasm. Soon after the spermogonia have begun to develop certain hyphae near the lower epidermis of the leaf become entwined to form more or less spherical coils, the primordia of the ascocarps. Their apices project in groups of tour or five through the stomata, and the terminal cells become i64 PYRENOMYCETES [CH. swollen and apparently mucilaginous; these projecting filaments were re- garded by Frank as trichogynes, but more recently Brooks has found evi- dence that they arise from the outer cells of the perithecium and that, what- ever their origin, they now no longer function as receptive structures. Sper- matia are often found attached to their terminal cells, but, in view of the enormous number of spermatia liberated on the under surface of the leaf, they could hardly fail to be found in relation to any projecting filament. In the lower part of the coils certain cells become differentiated by their denser cytoplasm and larger nuclei, and no doubt represent the oogonial regions of the archicarps. No union of nuclei has however been observed in them and it is at least doubtful whether they give rise to the ascogenous hyphae. The latter do not become clearly differentiated till the oogonial cells have disappeared ; asci are formed either from the terminal or sub- terminal cells; in the young ascus two nuclei fuse. Throughout the divisions in the ascus and in the division of the spore nucleus Brooks has reported four chromosomes. Those in the first division in the ascus are short and thick, resembling heterotype chromosomes in appearance, and there seems reason to believe that reduction occurs at this stage. The life-history of Gnomonia shows many points in common with that of Polystigma ; both are at first leaf parasites, and complete their develop- ment saprophytically on the dead leaf. Both produce spermogonia with filiform spermatia and perithecia developed in relation to coiled archicarps. An important point of difference is that in Polystigma a stroma is formed and the fungus hibernates on the fallen leaves below the tree without being injured by their decay; in Gnomonia no stroma is present and the fungus inhibits the formation of the absciss layer so that the withered leaves remain on the branches and provide a matrix in which the perithecia can be formed. GNOMONIACEAE : BIBLIOGRAPHY 1886 Frank, B. Ueber Gnomonia erythrostoma, die Ursache einer jetzt herrschenden Blatikrankheit der Susskirschen im Altenlande, nijbst Bemerkungen uber Infection bei blattbewohnenden Ascomyceten der Baume uberhaupt, etc. Ber. der deutsch. Bot. Gesell. iv, p. 200 1910 BROOKS, F. T. The Development of Gnomonia erythrostoma, the Cherry-Leaf-Scorch Disease. Ann. Bot. xxiv, p. 585. Valsaccae The perithecia of the Valsaceae are produced frequently in compact groups on a black stroma from which their long necks alone project. I he stroma is very variable in form ; it is developed within the substratum and more or less differentiated from it, sometimes indicated only by a black stain on the wood or bark of the host and by a black margin, sometimes v] SPHAERIALES 165 ex tended as a thin black layer over a considerable area and ending irregularly; sometimes, as in species of Valsa, forming1 black cushions erumpent through tin- hark of the host. In a few cases the stroma surrounds only the upper part and not the base of the perithecium, and we have thus a transition from the rudimentary stromata of some of the earlier families. I he peridium is black and leathery, the asci usually long stalked, the spores uni- or multicellular, and hyaline or dark-coloured. ( lonidia are frequently present, borne on free conidiophores or produced within pyenidia. The genus Valsa includes some four hundred species and Diaportke a rather larger number. The majority are saprophytic on wood and other re- sistant parts of plants. Diatrypaceae In the Diatrypaceae the stroma is developed under the bark of the host, and forms either a cushion or a thin, flat layer which later becomes exposed. Conidia of various kinds are produced, but the conidial and perithecial tromata are often distinct and whereas the latter are of the usual dark colour and carbonaceous consistency the former are frequently light-coloured and flesh}-. This separation and the usually unicellular, small, hyaline, curved ascospores are the principal characters of the family. The genus Calosphaeria is exceptional in lacking a perithecial stroma; its perithecia are free and it could appropriately be placed in one of the groups near the Pleosporaceae but that a conidial stroma is present and closely resembles that of the Diatrypaceae; the ascospores, moreover, are of the characteristic curved form, so that Calosphaeria may, it appears, more fitly be regarded as a reduced member of the group. The species of Calo- spliacria, like the other Diatrypaceae, occur chiefly on dead wood but C. princeps infects the living branches of cherry, plum and peach. In Diairype the most characteristic stroma is a black corky tissue of indefinite extent in which the perithecia are completely immersed ; the ascus contains eight spores in contrast to the numerous spores of certain species of Calosphaeria and of Diatrypclla, a genus further distinguished by the cushion- shaped stroma. Xylariaceae The Xylariaceae occur chiefly on wood ; they represent the highest development of the Sphaeriales and are characterized by the free superficial stroma which is only very rarely, as in Hypoxylon, partly sunk in the sub- stratum, and shows every variety of form from a spreading crust on the surface of the host, as in the genus Nummularia, some species of which 1 66 PYRENOMYCETES [CH. approximate Diatrypc, to the almost spherical cushions of Hypoxylon (fig. 123) and the erect, simple, or branched stromata of Xylaria (fig. 124) and its allies. The perithecia are arranged just below and at right angles to the surface of the stroma; their development may be preceded by the formation of conidia which often cover the young stroma with a whitish powder. Fig. 123. Hypoxylon coccineum I'.ul the smallest stroma bears conidia, the others perithi after Tulasne. Poronia punctata occurs on old horse dung; the stromata are about 1 cm. in height, stalked and expanded above into a cup or disc (fig. 125), which, in the earlier stages of development, is covered by a greyish-white film of conidia ; later the ostioles of the numerous perithecia appear as black dots scattered over the surface of the disc (fig. 126). The asci, when ripe, protrude through the ostiole so that the dark brown spores are shed outside the perithecium. Dawson was able readily to obtain pure cultures, both from the asco- spores and from the conidia, on 10 per cent, gelatine made up with decoction of horse dung. The ascospore forms a single lateral germ-tube, which develops septa and branches freely. The conidia produce germ-tubes from either end or from both and sometimes also laterally; the mycelium is at first much more delicate than that derived from the ascospores but soon becomes indistin- guishable from it. Branches arise from points just below the cross walls ; v] SPHAERIALES 167 frequent lateral anastomoses occur and crystals of calcium oxalate, which have become separated from the substratum, arc found among the filaments. Hyphae become massed together to form the stroma which in the very young stages consists entirely of vegetative filaments densely inter- \ . ■ Fig. 124. Xyiaria HypoxylonGtev., after Tulasne. woven and rising vertically from the surface of the substratum. As they grow the stromata assume their characteristic shape, conidia appear and drops of pinkish or yellowish fluid are exuded. When these dry up, black dots indicating the position of the ripening perithecia are seen. 1 68 PYRENOMYCETES [en. Fig. i 2 5. Porottia pitnc/ala (L. ) Fr. ; rt. surface, ^. lateral view; after Tulasne. Fig. 1:6. Poronia punctata (L.) Fr. ; stroma cut across; after Tulasne. v] SPHAERIALES [(',., The perithccium is initiated by the development of a coil of large, deeply-staining cells forming the archicarp. It arises amongst the vegetative filaments of the stroma, forms a couple of loops and is continued towards the surface of the stroma as a slender multicellular trichogyne (fig. 127 cj). At an carl)- stage the coiled portion becomes surrounded by a knot of small, densely -staining hyphae ; later the trichogyne disappears, degeneration progressing from the base to the apex ; the investing filaments grow more actively on the side of the archicarp towards the surface of the stroma, so that the young perithecium becomes pear-shaped (fig. 127^, c)\ further growth renders it hollow, and the upper part becomes lined with delicate periphyses (fig. 127 d). At the base of the developing perithccium is a group Fig. 127. Poronia punctata (L.) Fr. a. archicarp, x 27; ; b. <'. and d. young perithecia, x 205; after I >aws< in. of stout, deeply-staining hyphae, from which the asci arise and which occupy the position of the coiled archicarp in earlier stages. Later the base and sides of the perithecium are covered by numbers of filiform, septate para- physes, and amongst these the asci develop. It seems pretty clear that the trichogyne now no longer functions; this is borne out by the fact that degeneration proceeds from its base upwards and not from its apex, as might have been expected if a male nucleus were travelling down. It is probable, though it has not actually been demon- strated, that the ascogenous hyphae are derived from the archicarp, but in view of the complete degeneration of this organ in Gnomonia, it is not safe to conclude without further evidence that it is still functional in Poronia punctata. The species deserves further investigation, especially from this point of view. In both Xylaria and Hypoxylon the young stroma is covered by a tangle 170 PYRENOMYCETES [CH. of conidiophores, from which small oval conidia are abstricted. In Xylaria these form a white coating, in marked contrast to the older black portions of the stroma, where the perithecia are maturing, and justify the name candle-snuff fungus, applied to some of the commoner species. If, in either genus, the stroma be sectioned during the conidial stage, nests of small hyphae, similar to those in Poronia, will be found, and are the first indica- tions of the perithecia. Sometimes a stouter hypha with larger nuclei, presumably an archicarp, is recognizable (fig. 12S), but it has not been shown to function, and there is no evidence of normal sexuality. It is however not unlikely that some of these species, which are conveniently easy to microtome, will repay further investigation. At a later stage ascogenous hyphae are readily recog- nizable (fig. 129). Fig. 128. Xylaria polymorph/* (Pers.) Grev. ; archicarp embedded in stroma, x iooo. Fig. 129. Xylaria polymorpha (Pers.) Grev.; septate archicarp, x iooo. XYLARIACEAE: BIBLIOGRAPHY 1861-5 TULASNE, L. R. and C. Selecta Fungorum Carpologia; Imperial-typograph., Paris. 1900 Dawson, M. On the Biology of Poronia punctata (L.). Ann. Bot. xiv, p. 245. v] LABOULBENIALES 171 Labi ni.r.i.N iai.es The group Laboulbeniales includes some six hundred species arranged in over fifty genera. All are minute external parasites on insects, chiefly on members of the Coleoptera. They appear to do but little injury to the host, inducing at must a slight irritation but never causing death, indeed their own existence depends on that of the insect to which they are attached since, unlike many other fungi, their life ends with that of their host. The Laboulbeniales are all of fairly simple structure (fig. 130) and show an underlying similarity of type. In all cases the vegetative part consists of a receptacle, usually two-celled, attached to the integument of the host by a blackened base or foot. From the receptacle grow out filamentous appen- dages on or among which the male organs are produced and, with a few- exceptions, the receptacle of the same individual also gives rise to a female organ fr< im which a perithecium liberating ascospores is eventually developed. The plant is covered by a thin, homogeneous membrane which is ex- ceedingly tough and impervious and is developed from the gelatinous coat of the spore; it efficiently protects the cells from desiccation. Within this envelope the cell walls (except those of the receptive parts of the trichogyne and of the internal cells of the perithecium) are very thick and laminated. In certain cases, and especially in the genus Laboulbenia, they are traversed by fibrillae which arise from the innermost wall layer and are attached to the inner surface of the envelope. The cells are uni- nucleate (fig. 131) with rather dense, granular or reticulate cytoplasm and F'g- l.i°- Laboulbenia triordinata Thaxter ; 13= after Thaxter. ; r . Laboulbenia ehaetophora young perithecium and tricho- gyne, 360 ; after Fault. PYRENOMYCETES [CH. contain oil globules. Between adjacent cells that have the same origin the protoplasm is continuous through broad pits. The cytoplasm on each side dips into the pit, forming a thick strand which, in Laboulbenia at least, appears to be intersected by the middle lamella (Faull). The latter in favourable cases is seen to be perforated by one or more fine pores through which com- plete continuity is established1. There is evidence that a stout strand of cytoplasm unites contiguous cells in the appendages. The spores are remarkably uniform throughout the group, being in- variably hyaline and fusiform or acicular in shape and almost invariably two-celled (fig. 132). The cells are commonly of unequal size, that nearest the apex of the ascus being the larger, and both are uninucleate. The spore is clothed in a gelati- nous sheath especially well developed about the upper end which, when the spore is discharged from the perithecium, is destined to come in con- tact with the integument of the host. Here the gelatinous mass enables the spore to take up the oblique position in which germination occurs. The lower extremity of the spore (its apex while in the ascus) forms the foot. As a rule the gelatinous envelope in this region becomes hard, opaque, black and more or less elastic and thus, while adhering firmly to the substratum, it may give the plant a certain freedom of movement. This elasticity is found especially in forms on sub- merged and rapidly swimming hosts where it allows the parasite to lie back along the body of the insect. Sometimes the foot is cut off from the rest of the plant by a wall, more often it is continuous with and forms part of the basal cell of the receptacle. In the great majority of cases it does not penetrate into the substance of the host but is in contact with the surface by a thin membrane through which materials are absorbed into its cavity. There are a certain number of forms, however, especially those occurring on soft-bodied insects or on the soft parts of others, in which a definite rhizoidal apparatus is developed and penetrates the body of the host. These species show no greater vegetative luxuriance than other members of the group and apparently do not benefit by their more elaborate absorptive organ. The receptacle, like the foot, develops from the lower segment of the spore. It consists, in the simplest cases, of two superposed cells and (in 1 A similar type of pitting has been described by Kienitz-GerlofT for the Red Algae ("Neue Studien iiber Plasmodesmen, " Ber. d. deut. bol. Gesel. xx, 1902.) fig- '3-- Laboulbenia elon- gata Thaxter; bicellular spore; after Thaxter. v] LABOULBENIALES i"3 monoecious forms) hears the appendages in a terminal position and the pcrithecium laterally (fig. 136). More rarely the receptacle consists of a larger number of cells variously arranged and reaching a considerable complexity in such forms as Zodio- myces vorticellarius (fig. 133). One or more appendages are borne on the receptacle. These are more or less filamentous and often elaborately branched. They bear the male organs and serve also lor the protection of the delicate trichogyne and perhaps facilitate fertilization by holding a drop of water around the organs con- cerned. The primary appendage is developed from the upper segment of the germinating spore and is terminal ; the later formed secondary append- ages, when present, are outgrowths from the cells of the receptacle. The male element is a non-motile cell which as early as 1896 was homologized by Thaxter with the spermatium of the Red Algae. The latter organ has now been shown to be an antheridium1 in which the nuclear divisions are reduced to one, or have altogether disappeared ; it is liberated entire from the male plant and carried passively to the female organ. It seems very probable that in the simplest cases, where they are produced externally at the tips of more or less specialized branches (fig. 1 34), Fig- 133- Zodiomyces vorticellarius Thaxter; after Thaxter. I [34. Ccratomyces rostra' III.- I ll.lMrl ; spermatia ; alter Thaxter. 1 Wolfe, Ann. Bot. xviii, 1004. Yamanouchi, Bot. Gaz. Ixii, [906. 174 PYRENOMYCETES [CH the " antherozoids " or spermatia of the Laboulbeniales have the same signi- ficance as those of other fungi. They fall off when mature and the cells from which they were formed may give rise to others in the same position. In Coreomyces instead of a segment of the branch being detached to form the spermatium, a portion of its contents is extruded. This arrangement leads to the more specialized endogenous organ which is found in Stigma- tomyces (fig. 136) and in many other forms. Here the naked mass of proto- plasm cut off from the parent cell may be regarded as the homologue of the spermatium, or the parent cell may be recognized as an antheridium and the detached segments as non-motile spermatozoids. They function, in any case, as sperms or male elements. They are detached from the contents of a flask-shaped cell and are extruded through an elongated neck opening at maturity to the exterior. Between the neck and the venter a diaphragm 1 >f cellulose is deposited and is perforated by a narrow opening so that the sperms are nipped off as they' pass into the neck. They are uninucleate, the nucleus of the parent cell undergoing successive divisions so that a series of sperms are produced. The parent cell has been termed an antheridium but if the spermatium is antheridial in character the name cannot appropriately be used for the cell in which it is borne, though the term spermogonium is applicable. These sperm-forming organs may be produced singly or in groups, each with its neck opening independently to the exterior, or they may form com- pound structures ( fig. 135), the necks of several cells penetrating a single adjacent cell into the cavity of which the sperms are discharged and from which they escape by a common duct, the so-called secondary neck, which may be a mere extension of the cell forming the common cavity or, in a few cases, may involve other cells also. The individual sperms are formed in much the same way in the compound as in the simple organs, but instead of being cut off from the parent mass of protoplasm by a diaphragm at the base of the primary neck they remain attached till the neck widens abruptly at its end, and they are extruded into the common chamber. Hundreds, or even thousands, may be formed during the period of activity of a single compound organ. The exo- genously produced sperms are always walled where- as those formed endogenously are naked when first set free ; later a thin wall may be secreted. The female organs are formed from the basal cell of the spore and are thus necessarily lateral. This condition is often obscured in the mature plant where the developing perithecium may push Y Fig. [35. Dimerotnyces Afri- canus Thaxter; compound spermatial organ ; after Thaxter. v] LABOULBENIALES 175 the appendages aside and take up an apparently terminal position. The development is very uniform, and has been described by Thaxter in some detail for Stigmatomyces Baeri. Here, the upper cell of the receptacle divides into two; the lower of these remains as part of the receptacle, and the upper grows out (fig. 136**) to form the female organ and ultimately Fig. [j6. Stigmatom) Peyritsch; development of the perithecium ; o. shows the two-celled receptacle, a single appendage bearing five simple, endogenous spermatial organs, and the beginning of the perithecium ; l>. — ;'• indicate successive stages in the development of the perithecium : the trichogyne first appears in d. ; in e. spermatia are being shot out and some are attached to the trichogyne : in »". two of the four ascogenous cells are shown, with the superior steiile cell above them, and the primary and secondary inferior sterile cells below; after Thaxter. the perithecium. It divides transversely, the upper of its daughter cells gives rise to the female organ, the lower divides several times (fig. 1366), and ultimately forms the double wall of the perithecium, a function fulfilled by a complex of neighbouring hyphae in Ascomycetes with a richer vegetative development. The upper cell, the initial of the female organ, divides, separating the female cell below (fig. 136c) and a cell above, which divides once more to form the terminal trichogyne and the subjacent trichophoric cell (fig. 136./). \-]6 PYRENOMYCETES [ch. All the cells are uninucleate. The female cell is called by Thaxter a carpogonium or carpogonic cell in conformity with the term used for the Red Algae, but it obviously corresponds to the cell in which fertilization is now known to occur in other Ascomycetes and will therefore here be termed the oogonium. In Stigmatomyces Baeri the trichogyne is simple (fig. 1^6 d, e) but in many other members of the group it undergoes frequent septation and branches freely. The apices of the branches are alone receptive and may straight or spirally coiled (fig. 137). However elaborate, the trichogyne quickly disappears, collapsing and breaking off as soon as its function is fulfilled. In endogenous species the sperms are shot direct on to the trichogyne or carried to it by the water which ordinarily surrounds these filaments when the hosts are hiding in moist places. In Zodiomyces on the other hand, where the spermatia are formed externally, they fall off the parent branches on to the cup-shaped receptacle, and there appear to be sought by the trichogyne which is at first bent over (fig. 1 38 tz) and later lifts itself after a spermatium has become attached (fig. 138$). Fig. 137. Compsomyces verticillaius Thaxter ; after Thaxter. Fig. 13K. Zodiomyces vorticellarius Thaxter; trichogyne a. before and b. after attachment of spermatium ; after Thaxter. In any case numerous male cells reach the trichogyne and, though the actual process of fertilization has not yet been seen, it appears likely that it is accomplished. Afterwards the oogonium divides into three superposed cells, the sterile inferior cell, the sterile superior cell and a fertile cell lying between the two (fig. 136^, //). This middle cell cuts off a secondary sterile cell below (fig. 136/) which like the other sterile cells is eventually destroyed. It then divides longitudinally into four "ascogenic" cells, two of which are shown in v] L.MUiU. KKNIAI.ES i/V fig. 136/, and from these asci hud out, arising in a more or less distinctly double row (fig. 1391/ 1. Some \ ariation occurs in different species in the later divisions and in the number of ascogenic cells. In Polyascomyces (fig. 140) more than thirty arc present, covering a basal area from which numerous asci bud upwards, so that the condition approximates that in other Ascomy- cetes. Faull describes the ascogenic cells as binucleate, each containing two Fig. 139. Stigmatomyees Baeri Peyritsch; a. young : b. ascus containing four spores; c. mass of spores in perithecium ; after Thaxter. Fig. 1 40. Polyascomyces Tricho- phyae Thaxter; after Thaxter. nuclei which undergo conjugate division whenever an ascus is formed. As a result the young ascus is binucleate and nuclear fusion followed by three divisions takes place in the usual way. As a rule four only of the eight nuclei function; the spores are produced in a manner quite characteristic of the Ascomycetes generally. In the ascus they are usually disposed more or less definitely in pairs and the members of a pair are discharged together from the perithecium and germinate side by side. In monoecious species one member of a spore pair may frequently produce a smaller and weaker individual than the other, while in Laboulbenia inflata the atrophy of one at an early stage of development is a regular phenomenon. In Stigmatomyees Sarcophagae the smaller individual is uni- sexual, producing only male cells, while the larger is hermaphrodite (fig. 141). In dioecious species the paired spores are of rather different sizes. The smaller spore gives rise to a male plant, the larger to a female, so that by their association at a point of contact with the host a condition essential for the perpetuation of such species is secured. The cytological changes by which this segregation of sex is brought about between the members of a pair should be of great interest and demand investigation. c.-v. i78 PYREXOMYCETES [CH. There is an obvious suggestion in these phenomena of a transition between the monoecious and dioecious condition but it is not clear in which direction the series should be read. It might be inferred that the male plant had become atro- phied after the female had acquired spermatial organs, or on the other hand that, as in many other groups of plants, a hermaphrodite con- dition was primitive and segregation a later development. Amorphomyces Falagriae may be taken as an example of a dioecious form which shows also several other peculiarities. The spores are unique amongst those of Laboulbenialesin being aseptate (fig. 142). The difference between the spores producing male and female plants is slight at first but becomes very apparent on germi- nation. In each case the spore divides into three superposed cells (fig. 143 a), in the male the terminal cell elongates and forms a single male organ liberatingendogenous sperms. The second cell maybe regarded as the basal cell of this struc- ture and the lowest as a unicellular receptacle, or they may be held to constitute together a two-celled receptacle. There are no appendages. In the female the lowest cell, which may become partly divided, forms the receptacle, the next above gives rise to the perithecial wall and the terminal cell to the female organ proper. The perithecium and its contents are therefore here terminal, a state of affairs not met with elsewhere in the group. The terminal cell divides in the usual way to form an oogonium, a tricho- phoric cell and a trichogyne ; the latter is short and branching (fig. 143 £). The development of the perithecium (fig. 144) seems fairly typical and the asci apparently contain four spores. Fig. [41. Stigmatomyces Sarco- \n 1912, Faull published an account of the phagae Thaxter; male and her- . . n. aphrodite individuals, x -.do; cytology of two species of Laboulbema, L. chaeto- after Thaxter. phora, and L. Gyri.nida.rum. Both occur on the same host, and could not be distinguished in the young stages. Both are parthenogenetic, no male cells being formed. v] LABOULBENIALES 179 A trichogyne, trichophoric cell and oogonium arc formed in the usual way (fig. i,i). Accordingto Faull nuclear division takes place both in the oogo nium, and in the trichophoric cell, and the partition between these two breaks down so that a long cell containing a row of four nuclei is formed (fig. 145 a). Fig. 142. Amorphomyces Fala- griac Thaxter ; paired spores ; after Thaxter. Fig. 143. Amorphomyces Falagriac Thaxter; male and female individuals; a. young, b. mature; after 'I'll, i . r. Walls cut off the upper and the lower nucleus, and a central binucleate cell is left, the lower nucleus of which is presumably a daughter of the oogonial and the upper of the trichophoric nucleus. These divide simultaneously and a binucleate inferior sterile cell is separated from the binucleate fertile cell. This in turn divides to form the ascogenic cells, from which the asci are to develop, and these and the asci which they produce are therefore binucleate. The two nuclei in the ascus fuse and their union is regarded by Faull as the only nuclear fusion which occurs in this very curious life history. Meiosis then takes place, followed by the third division. The upper daughter nuclei of this division degenerate and around the lower nuclei spores are organized. In each spore the nucleus divides once and a transverse septum is formed. Faull describes four chromosomes (fig. 145 c) at ever)- sta^e but figures an apparently larger number in the first division in the ascus where the structures repre- sented are evidently gemini (fig. 145 /;). 1 he Laboulbeniales are subdivided by Thaxter ac- cording to the method of formation of the male cells, Fig. 144. .hiiorpho- Falagriac Thaxler ; male and female individuals, the latter with peri- thecium containing re ; aftei I ter. 12 — -2 i8o PYRENOMYCETES [CH. whether exogenous or endogenous, and in the latter case whether produced in simple or compound organs. In this way three families, Peyritschiel- laceae (compound endogenous), Laboulbeniaceae (simple endogenous) and Ceratomycetaceae (exogenous) are distinguished. f ., ■■ ■:\\. ■ ' 9 ■ . . .. ■■:-;■■ b Fig. 14J. Laboulbenia chaetophora (?). «. cell formed by binucleate oogonial and trichophoric cells, x 430 ; b. first division in ascus described by Fauil as the anaphase, K1510; c. nuclear division in spore, showing four chromosomes, X2800; after Faull. Since almost all our knowledge of the group is due to the brilliant work of Professor Thaxter of Harvard it follows that the North American species are far better known than those of other localities. Such material as he was able to obtain from warmer regions proved, however, exceedingly rich in representatives of the group, and it is probable that further study will show them to be widely distributed. The known European species are few, and only two have been identified in Great Britain. The systematic relations of the Laboulbeniales are not easy to deter- mine. They are pretty evidently monophyletic, and are highly specialized along lines dependent on their peculiar habitat. The form and develop- ment of the ascus is typical of the Ascomycetes, and the Laboulbeniales clearly belong to that group, though it is difficult to indicate their affinities within it. In the Laboulbeniales the young female branch consists of four parts, the initial cell of the perithecium wall, the oogonium (carpogenic cell of Thaxter), the trichophoric cell and the trichogyne. These correspond pretty clearly with the archicarp of other groups. The initial cell of the perithecium wall constitutes a stalk-cell from which the enveloping hyphae develop. The trichophoric cell should probably be included as part of the trichogyne, which in this sense always consists of at least two cells. After fertilization the oogonium divides to form a row of cells, which are, from below upwards, v] LABOULBENIALES 181 the inferior sterile cell, the secondary inferior sterile cell, the mother-cell1 of the ascogenic cells and the superior sterile cell. The subterminal of these all me gives rise to asci ; this it does by dividing longitudinally into a definite number of ascogenic cells from which the asci arc budded out. \ multicellular trichogyne is not uncommon among Ascomycetes, and the division of the oogonium after fertilization into a row of cells is a well-known phenomenon occurring among Plectascales, Erysiphales, and 1 liscomycetes. In most cases several cells of the septate oogonium give rise to ascogenous hyphae, but in the Erysiphales only the subterminal cell ot the row does so. In Etysipke this cell, which always contains at least two nuclei, gives rise to several asci and differs from the sub- terminal cell of the Laboulbeniales chief!}' in the fact that the asci are produced from short outgrowths instead of, as in Stigmatomyces and its allies, from daughter cells formed by longitudinal division. In this character then, the Laboulbeniales would appear most nearly to approach the Erysi- phaceae, which they also resemble in the formation of the sheath from the stalk cell of the oogonium, but they differ from them in possessing a tricho- gyne, an organ not known in that group, where the antheridium comes into direct contact with the oogonium. The Laboulbeniales and Erysiphaceae have also in common the uni- nucleate character of their vegetative cells. In the structure of their ascocarp, opening as it does by a narrow aperture, tin- Laboulbeniales approach most closely to the other Pyrenomycetes. The male element in the Laboulbeniales is a non-motile, uninucleate structure which may be budded off externally from the parent cell, or extruded from it as a naked mass of protoplasm. Amongst the Fungi spermatia occur in the Pyrenomycetes and Lichens and also characterize the Uredinales, but in all these cases they are budded off externally as walled structures. The spermatium both in the Red Algae and in the Fungi has been homologized with a reduced antheridium, and, as has already been pointed out, the exogenous male element no doubt bears the same significance among the Laboulbeniales. We have no satis- factory indication as to the relative primitiveness of the endogenous and the exogenous condition, but it may be noted that exogenous forms only an- known among Fungi other than Laboulbeniales. The endogenous organ may be derived from the branch which cuts off exogenous, walled spermatia. or it may represent quite a different response to the need for non-motile male elements, the parent cell being the honiologue of the antheridium and the fertilizing element that of a spermatozoid. These various characters, approximating to those of sometimes one, 1 This cell is described by Thaxter as the ascogonium. The word has acquired a somewhat rent sense in other Ascomycetes. i82 PYRExNOMYCETES [ch. v sometimes another group of Ascomycetes, seem on the whole to indicate no very close relationship, but suggest rather that the Laboulbeniales were derived from an ancestral form, already definitely ascomycetous but not otherwise highly specialized, and that they have undergone elaborate and characteristic modifications after branching off from the main line. Their nearest affinities are with the Erysiphales and Pyrenomycetes. The resemblances between the Laboulbeniales and the Red Algae have been regarded as significant in connection with the hypothetical relationship of the higher Fungi to that group. LABOULBENIALES: BIBLIOGRAPHY 1896 Thaxter, R. Contribution towards a Monograph of the Laboulbeniaceae, Pt. I. Mem. Am. Acad. Arts and Sciences, xii, p. 195. 1908 Biffen, R. H. First Record of Two Species of Laboulbeniaceae for Britain. Trans. Brit. Myc. Soc. iii, p. 83. 1908 Thaxter, R. Contribution towards a Monograph of the Laboulbeniaceae, Pt. II. Mem. Am. Acad. Arts and Sciences, xiii, p. 219. 191 1 Faull, J. H. The Cytology of the Laboulbeniales. Ann. Bot. xxv, p. 649. 1912 Faull, J. H. The Cytology of Laboulbenia chaetophora and L. Gyrinidarum. Ann. Bot. xxvi, p. 325. CHAPTER VI BASIDIOMYCETES THE Basidiomycetes include over i 3.000 species pi assessing a well-developed mycelium, which, among the higher forms, builds up an elaborate fruit-body such as may be observed in the toadstools, bracket fungi and puff balls. They are characterized by the fact that their principal spores, the basidio- spores, arc borne externally on the mother-cell or basidium. The young basidium contains two nuclei ; these fuse, and the fusion nucleus divides twice, providing the nuclei of the four spores : each spore is formed at the end of a stalk or sterigma through which the nucleus passes to enter the developing spore. The two divisions in the basidium constitute a meiotic phase. In the Autobasidiomycetes the basidium is without septa, and the spores, except where some fail to develop, are regularly four in number for each basidium. In the Protobasidiomycetes the basidium is divided into four cells, each of which gives rise to a single spore ; the walls are transverse in the Uredinales and Auriculariales, longitudinal or oblique in the Tremellales. In the Hcmi- basidiomycetes (Ustilaginales) septa may or may not be present in the basidium, but the fusion nucleus divides more than twice, and more than four spores are produced. In Puccinia, P hragmidium and other Uredinales, and in Sirobasidium and its allies, the basidia are developed in chains, in other cases they are borne singly. In the Ustilaginales and in the majority of the Uredinales the nucleus and cytoplasm of the basidium are at first enclosed in a thick wall forming the brand-spore or teleutospore cell, which becomes detached, form- ing an additional means for the distribution of the plant; later the contents are extruded as a thin-walled promycelium on which the basidiospores are produced. In other Basidiomycetes the basidia are thin-walled throughout their development and produce spores while still attached to the mycelium. The basidiospore is unicellular, round or oval in shape, usually with a smooth, rather thin wall. Echinulate or warted spores occur in a few species, and in many families, especially among gill-bearing fungi, dark or bright-coloured spores are common. In a considerable number of genera accessory spores are also produced. Except for th production of their characteristic spores externally on basidia, the Ustilaginales and Uredinales differ in almost even- particular from the majority of the Basidiomycetes; they arc obligate parasites with a delicate mycelium ramifying in the tissues of the host and they lack the elaborate stroma characteristic of the Autobasidiomycetes. It has therefore seemed advisable to deal with them as distinct groups, separating them for purposes of description from the Basidiomycetes proper. CHAPTER VII HEMIBASIDIOMYCETES USTILAGINALES THE Ustilaginales, Brand fungi, Smuts or Bunts, constitute a group of some 400 obligate parasites on the higher plants, giving rise in the tissues of the host to characteristic, usuallydark-coloured resting-spores, the brand-spores, teleutospores or chlamydospores. These are developed in considerable quantities, either singly, in pairs, or in clusters known as spore-balls, and when ripe break through the host tissue, forming a pustule or sorus. No distortion of the host is caused during the period of vegetative growth, but in preparation for the formation of spores very considerable hypertrophy may be induced. Ustilago Treubii on the stem of Polygonum chinense in Java causes the formation of elaborate galls (fig. 146) provided with vascular tissue and growing by means of a cambium; Ustilago Maydis produces whitish swellings and blisters, often as large as a fist, on the stem, leaves, roots, and especially the flowers of Zca Mays; and Urocystis F/o/rt^deforms the stems and leaves of various species of Viola. Several other smuts develop their spores in the ovary of the host plant, or infect the stamens, filling the anthers with spores and benefiting by the means of distribution provided for the pollen. Ustilago antherarttm^ even induces development in the staminal rudiments of the normally pistillate flowers of Lychnis dioica. The stamens formed undergo dehiscence as usual and differ from those of the male rig. 146. Ustilago Treubii Solms ; stem of Polygonum with " fruit gall," nat. size ; after flowers only in the presence of fungal Solms Laubach. spores instead of pollen in theiranthers. In all these cases and in most of the Ustilaginales spore-formation is strictly localized, but in the genus Entyloma and its allies spores may be formed at almost any point. 1 Ustilago antherarum (DC.) Fr. = Ustilago violacea (Pers.) Fuck. (II. VII USTILAGINALES i8s The mature brand-spore is uninucleate, and is surrounded by a delicate endospore and by an epispore which may be smooth or variously sculptured and usually contains pigment, giving the spore a black, brown, or violet colour. On germination the spore gives rise to a short tube, the promycelium or basidium (fig. 147), into which its contents pass, the nucleus undergoing at Fig. 147. Ustilago Scabiosae Sow.; development of basidium; after Harper. least two divisions; the basidium in turn produces a number of uninucleate sporidia or basidiospores. The basidium may be unicellular, giving rise to a bunch of basidiospores at its apex (Tilletia (fig. 148c?)), or multicellular, usually four-celled, producing one or more basidiospores from each cell {Us- tilago (fig. 147 e)). The nucleus of the parent cell does not travel into the basidiospore but divides, sending one daughter nucleus into the spore, while the other, remaining in the basidial cell, may undergo further divisions so that nuclei are provided for a number of spores. I'nder suitable conditions the basi- diospores are cut off in considerable numbers. They may further multiply by budding, giving rise to conidia, or a delicate mycelium may be formed from which conidia are abstricted ( Til- letia), A supply of conidia is produced by these means in dung decoction and other nutrient solutions, and no doubt in the damp, manured soil of the Fig. 148. Tilletia Tritici (Iijerk) Wint. ; a. basidium thirty hours after germination of brand-spore; 0. after conjugation of basidio- spores; x 300 : after Plowright. 1 86 HEMIBASIDIOMYCETES [CH. Fig. 149. Ustilago antherarum Fr.; a. and b. conju- gating basidiospores; c. conjugation between a cell of the basidium and a basidiospore; after Harper. fields. As a rule the conidia are of the same oblong form as the basidio- spores, but, in the genus Tilletia and some of its allies, they may be stout or sickle-shaped, whereas the basidiospores are long and narrow. In Entyloma the brand-spores are capable of germination on the tissues of the host leaf, where they give rise to hyphae which penetrate through the stomata and form basidia from which basidiospores are produced. During their development the cells of the basidium, the basidiospores, or the conidia budded out from them, may become united in pairs (figs. 148 #, 149), by means of a tube of variable length put out by one or both participants and recalling somewhat the con- jugation tube of the Zygnema- ceae. The growth of these tubes is very accurately directed and appears to depend on a chemo- tropic stimulus. In the majority of cases the nucleus of one of the associated cells passes down the tube into the other, but does not fuse with its nucleus (fig. 150). Later both nuclei divide, and a mycelium of binucleate cells is produced. It is on this mycelium that the infection of the host depends ; it penetrates the tissues usually of the seedling, but sometimes of the developing parts of the mature plant, being in most cases derived from spores which adhered to the seed coat. These may be destroyed by dipping the seed into hot water or formalin solution before sowing. Once in the tissues of the host the binucleate mycelium penetrates in all directions, ramifying between the cells of the host and send- ing haustoria into them. The internodes of the stem are tra- versed by long, unbranched hyphae, but in the nodes branch- ing is frequent, and here also the majority of the haustoria are to be found. Where the host is perennial the mycelium perennates in it, and, if the host dies down during the winter, remains alive but quiescent in the upper part of the root stock till the growth of new shoots in spring gives it a fresh opportunity of development. Conidia have been recorded on the parasitic mycelium of Tuburcinia and Entvloma but are not of common occurrence at this stage. Fig. 150. Ustilago Hordei; conjugation; after Lutman. VII] USTILAGIXAI.KS 187 In the regions where the formation of brand-spores is to take place, the mycelium becomes richly branched and often swollen and gelatinous. In Ustilago and Sphacelotheca the sporogenous hyphae are divided into a number of short segments in each of which the contents form a spore surrounded by an independent membrane. The spores arc enclosed at first within the gelatinous parent walls, but later these disappear so that the whole mycelium is transformed into a pulverulent mass of spores In Tilletia and Entyloma the sporogenous cells are budded off laterally from the mycelium. In Tubitrcinia a number of richly septate hyphal branches become inter- woven, forming a knot or spore-ball in which spores to the number of 50 or 100 are developed from within outwards. In Urocystis the spore-ball is small and the outer cells remain pale or colourless and do not function as spores though they resemble them in form (fig. 151). In Doassansia the outer sterile cells are wedge-shaped, and in Sorosporium they form a gelatinous investment in which their individual boundaries are no longer recognizable. Fig. [51. Fischfri; -.pore- ball, one spore germinating, ■ ;oo ; after Plowright. Fig. 1-2. Ustilago Cario; u. young, binucleate brand-spores; b. "l. conjugation; after Harper. 192 HEMIBASIDIOMYCETES [CH. Basidiospores are budded off in abundance from all three cells, and in turn give rise to conidia. In the meantime the basidium has separated from its parent brand-spore, and the spore, after nuclear division, may produce another basidium, and others in succession at the same spot, so that free basidia accumulate in the culture. If cultures in nutrient solution are allowed to starve, association now takes place between basidial cells, basidiospores or conidia by means of conjugating tubes (fig. 1 58 £). The paired cells increase markedly in volume, but no interchange of cytoplasm takes place and the nuclei remain in their respective cellsvvithout visible change. Harper observed that when fresh beerwort was supplied to his cultures at this stage the produc- tion of conidia began again. They are produced from one or both of the con- jugating cells, but only a single nucleus is concerned in the development of each conidium, the other remains quiescent and the conidia are uninucleate. In a host plant, the name of which is not recorded, Werth and Ludwig failed to find binucleate elements, the youngest cells in which they could iden- tify the nuclei being uninucleate (fig. 139 a). They infer that in this species nuclear association fails to take !»0* place, and no binucleate stage exists. This hypothesis accords well with Harper's observations on the saprophytic phase which he studied in material grown on Lychnis alba. On the other hand, a binucleate stage was identified by him in the sporogenous cells of U. an- therarum on Saponaria, and by Dangeard on Lychnis dioica. These facts suggest the possibility of two or more varieties of U. antherarum on different hosts and differing in their cytological behaviour; the forms studied by Dangeard and Harper point to a condition comparable to that of U. Maydis, while Werth and Ludwig's observations indicate the possibility of a truly apogamous strain. A complete life-history of this fungus, in material obtained from a single host, would probably prove of interest. Another possibly apogamous form is Ustilago levis, a common smut on oats. According to Lutman the hasidio- spores give rise to considerable numbers of conidia. These are multinucleate if formed in crowded masses, uninucleate when comparatively l^'l.ited. Germinated conidia found on the epi- dermis of infected seedlings usually contain two or three nuclei. The parasitic hyphae are multi- nucleate and their swollen ends, when spore- S.) Magn.; mycelium with formatjon js about to take place, contain ten to mu li uoeate and binucleate , cells; after Lutman fifteen nuclei. The final segments however are Fig. 159 Ustilago antherantm Fr.; a. young brand- spores h older brand-spores ; c. basidia; d. basidio- spores ; after Werth and Ludwig V Il| USTILAGINALES i93 uninucleate or binucleate (fig. i6o),but it is not known whether fusion takes place in them. The multinucleate character of the mycelial cells strongly suggests that no preliminary pairing of the nuclei occurs. In Ustilago Zeae Lutman also observed a mycelium of multinucleate cells; at the time of spore-formation binucleate and uninucleate cells and finally uninucleate spores appear. Tilhtiaceae The principal genera of the Tilletiaceae are Tilletia^ Entyloma, Tuburcinia, Urocystis and Doassansia. They have in common the continuous basidium with a terminal group of spores. Tilletia Tritici and T.foetens are the stink brands of wheat, so called by reason of the strong odour of trimethylamin or herring brine given out by the brand-spores. The two species differ in the character of the epispore which is smooth in T. foetens, reticulate in T. Tritici. In both cases spores are produced in the ovaries of the host, all tissues of which, except the outer coat, are destroyed. The spore masses are garnered with the crop, and damage all grains with which they are threshed or ground. The infected flour and contaminated chaff and straw are causes of disease in man and animals. On the germination of the brand-spore of T. Tritici the nucleus passes into the basidium and divides three times so that eight nuclei are formed. Eight basidiospores are budded off in a bunch at the apex of the basidium, and each receives a single nucleus. Frequently additional nuclear divisions take place and ten, twelve, or sixteen uninucleate spores may be produced. When the spores are fully formed short conjugating tubes grow out and connect neighbouring spi n'es, often while these are still attached to the basidium (fig. 161). According to Rawitschcr the nucleus of one cell of the pair passes over into the other and the nuclei lie near one another but without fusion. After con- jugation the spores may become septate; from those which contain two nuclei fila- ments of binucleate cells grow out, and may give rise to conidia which are also binucleate. Under suitable conditions the binucleate hyphae bring about infection by pushing between the cells of the host seedling. In the cells of the sporogenous mycelium fusion of the G.-V. 1 3 Fig 161. Tilletia Tritici (Bjerk) Wint.; a. basidium ihirly hours after germination 1 if brand-spore; /'. conjugation of basidio- spores : ■ .',oo: after Plowright. 194 HEMIBASIDIOMYCETES [ch. pairs of associated nuclei takes place. Rawitscher observed a quite similar life-history in T. lacvis. In the parasitic mycelium of Doassansia Alismatis and Entyloma Glaucii (fig. 162) Dangeard observed binucleate cells and the fusion of their nuclei Fig ifi:. Development of brand-spores ; a. Doassansia Alismalis 1 \rcs) Corn.; l>. Entyloma Glatuii Dang.; after Dangeard. in pairs in preparation for the formation of the brand-spores. The same stageswere recorded by Lutman mDoassansiadeformans,EntylotnaNynipheae and Urocystis Anemones (fig. 163). Fig. 163. Urocystis Anemones (Pers.) Wint.; mycelium and young spore ball ; afiei Lutman. Tuburcinia primulicola infects various species of Primula and gives rise to conidia as well as to brand-spores during its parasitic stage. Wilson has shown that the conidia develop in the young flower on a mycelium of uninucleate cells which apparently persists in the host plant throughout the winter. When the flower opens the conidia conjugate in pairs, and a nucleus passes through the connecting tube so that one conidium is empty and the other binucleate. Germ-tubes with paired nuclei are later produced and doubtless give rise to the mycelium of binucleate cells which bears the brand-spores. This mycelium ramifies in the superficial tissue of the placenta and between the ovules, giving rise to brand-spores in the same flowers in which the conidia were previously developed. On the germination of the vii] USTILAGINALES 195 brand-spores, basidia and basidiospores appear, but no conjugation could be observed. T. primulicola thus resembles the Uredinales in having two parasitic generations, the one with uninucleate, the other with binucleate cells. Its hibernating, uninucleate mycelium also recalls the parasitic mycelium of Ustilago Afaydis, or of U. Vaillantii, which consists of uni- nucleate cells. USTILAGINALES: BIBLIOGRAPHY 1S07 Prevost, B. Memoire sur la cause immecliate de la Carie. Fontanel, Montauban. 1.S47 Berkeley, M. J. Propagation of Bunt. Trans. I Ion. Sue. London, ii, p. 113. 1 S47- Tn VSNE, L. R. and C. Memoire sur les Ustilaginees comparers aux Uredindcs. Ann. Sci. Nat. 3 ser. vii, p. 12. 1853 DE Bary, A. Untersuchungen iiber die Brandpilze und die durch sie verursachten Krankheiten der Pflanzen. Miiller, Berlin. 1854 TULASNE, L. R. and C. Second Memoire sur les Urddinecs et Ustilaginees. Ann. Sci. Nat. 4 ser. ii, p. 1 13. J867 FISCHER von WALDHEIM, A. Sur la structure des spores des Ustilagindes. Bull. dc la Soc. Imp. des Nat. de Moscou, xl, p. 242. 1883 BREFELD, O. Botanische Untersuchungen iiber Hefenpilze. V, die Brandpilze. Felix, Leipzig. 1S87 zu Solms Laubach, H. Ustilago Treudii Solms. Ann.dujard. bot.de Buitenzorg, vi, p. 79. 1888 Ward, H. MARSHALL. The Structure and Life History of Entyloma Ranunculi (Bonorden). Phil. Trans, clxxviii, p. 173. 1889 PLOWRIGHT, C. B. A Monograph of the British Uredineae and Ustilagineae. Kegan Paul, Trench & Co., London. 1894 DANGEARD, P. A. Recherches histologiqucs sur la famille des Ustilaginees. Le Botaniste, iii, p. 240. 1899 HARPER, R. A. Nuclear Phenomena in certain stages in the development of the Smuts. Trans. Wisconsin Acad. Sci. Arts and Letters, xii, p. 475. 1904 FEDERLEY, H. Die Copulation der Conidien bei Ustilago Tragopogi pratensis Pers. Olversigt af Finska Vetensk. Soc. Forhandlingar, lxvi, No. 2, p. 1. 1910 M' A 1. pink, D. The Smuts of Australia. J. Kemp, Melbourne. 191 1 LUTMAN, B. S. Some Contributions to the Life-history and Cytology of the Smuts. Trans. Wisconsin Acad. Sci. Arts and Letters, xvi, pt. Ill, p. 191 1. [912 RAWITSCHER, F. Beitrage zur Kcnntniss der Ustilagineen. Zeitschr. f. Bot. iv, P- 673- 1912 Werth, E. and Ludwig, K. Zur Sporenbildung bei Rost und Brandpilzen, Per. d. deutsch. Bot. Ges. xxx, p. 522. K)i4 Massee, I. Observations on the Life-history of Ustilago Vaillantii, Tul. Journ. Ei on. Biol. i.\, p. 7. 1914 Rawitscher, F. Zur Sexualitat der Brandpilze Tilletia tritici. Lei. d. deutsch. Bot. I ies. xxxii, ]). 310. 1915 WlLSoN, M. The Life- History and Cytology of Tuburcinia primulicola Rostrup. B. A. Report, Sect. K. 1915. 13—2 CHAPTER VIII PROTOBASIDIOMYCETES Uredinales The rust-fungi, members of the group Uredineae, Uredinales or Aecidio- mycetes, including over 1 700 species, are without exception obligate parasites on the stems, on the sporophylls and especially on the leaves of vascular plants, usually on those of angiosperms or gymnosperms but in one or two cases of ferns. The mycelium ramifies in the tissues of the host, sends haustoria into the cells, and may act as a local stimulant causing more or less marked hypertrophy and consequent curling or malformation of the infected part. Starch may be stored by the host, and this is so abundant in the hyper- trophies caused by the aecidial mycelium of Puccinia Caricis on the nettle, Urtica parvifolia, that they are eaten by the Himalayans; one or two other species are similarly employed. Where the mycelium penetrates into the perennial tissues of the host it is itself perennial. Spores and Sori. On the mycelium several kinds of spore are produced, minute spermatia in spermogonia, aecidiospores in aecidia, uredospores and teleutospores, sometimes mixed, sometimes separate, in more or less definite sori. One or more of these types of spore may be lacking, but the teleuto- spores are almost invariably present, and it is on them that the classification of the group depends. Naturally enough it was some time before the various types of spore were recognized as belonging to the same fungus and the old generic names Fig. 164. Germinating teleutospores ; a. Phragmidium bulbosum Schm. ; b. Triphragmidium Ulmariae Lk.; c. Colcosporitim Sonchi Lev.; d. Uromy es appendiculatus (Fabae) Lev.; after Tulasne. (II. VIII] IRKIMXALKS ■97 of the spore forms other than t lie teleutospore, such as Aecidium, Caeoma and Uredo, still survive in our nomenclature. The teleutospores (figs. 164, 165, 166) may be unicellular or they may be made up of two or more cells forming a compound structure, each cell of Fig 165. Cronartium epiadeum Fr. ; te- leutospore mass with basiclia and spores; af- ter Tulasne. Fig. 1 66. Melampsora betulina Desmaz.; germinating teleutospores; after Tulasne. which germinates independently. The teleutospore is simple in Uromyces, Coleosporium, and Melampsora, it is two-celled in Gymnosporangium and Puccinia, it is built up of three to ten superposed cells in Phragmidium, and of a larger number in Xenodochus. In Triphragmidium it consists of three cells laterally placed and in Chrysomyxa and Cronartium the simple teleuto- spores are so massed together as to simulate compound forms: their real nature is revealed by their early separation one from another. One-celled teleutospores occur exceptionally in the two-celled species and are known as mesospores. The teleutospores may be massed together and incrusted in the tissues of the host, or they may be detached readily from their stalks and carried by the wind or by other agencies. Further development may take place as soon as conditions are favourable, or may be delayed till after a resting period, usually till the spring following development. In either case the nucleus in each cell ultimately undergoes two successive divisions, which constitute a meiotic phase, and the daughter nuclei are separated by transverse walls, so that four uninucleate cells arc produced. The telcutospore-cell thus functions as a tetrasporangium and divides into four portions, constituting the transversely septate basidium. from each cell a short, pointed branch or sterigma arises, its end dilates, a basidiospore 198 PROTOBASIDIOMYCETES [CH. (sporidium) is formed and receives the nucleus and cytoplasm of the cell from which it arose. In Coleosporium, Ochropsora, and Ckrysospora, nuclear division and septation take place within the teleutospore wall, and the basidiospores are budded out from it, so that the teleutospore cell becomes the basidium directly; in the majority of cases, however, the structure of the teleutospore is not such as readily to allow further growth, and development takes place after the extrusion of the contents as a tubular outgrowth, the so-called promycelium, surrounded only by a delicate membrane (fig. 167). The nucleus migrates into this structure and here nuclear division takes place, transverse septa are formed and the basidiospores are produced. But it must be noted that the nucleus and cytoplasm of the young basidium are those of the teleutospore cell, whether development takes place within the original wall or by means of a promycelium. When the basidiospore germinates its germ-tube penetrates through the cuticle of the host and forms a mycelium of uninucleate cells hearing spermogonia and aecidia. The spermogonium is usually found on the adaxial side of the leaf; it consists of a group of more or less parallel, unbranched, upwardly directed hyphae, arising from a small-celled tangle below the epidermis or cuticle of the host. In the majority of cases the outer hyphae of each group elongate to form paraphyses, so that the spermogonium is restricted in extent, and acquires a flask-shaped or pyriform outline; the paraphyses push up through the ruptured epidermis of the host to project at a narrow ostiole (fig. 16S b). In Fig. 167. Gymnosporangium davaricuforme Rees; germinating teleutospores ; x 666. Fig. 168. a. Phragtnidium violaceum Wint., X330; 6. Gymnosporangium clazariaeforme Rees, X260; sper- mogonia; after Blackman. Vlll] UREDINALES 199 Ki g. 169. Gymnosporangium clav&riaeforme Rees; development of spermatia, x 1 [N= ; after Blackman. simpler forms, such as Pkragmidium, the spermogonium is indefinite in extent, and consists of spermatid hyphae arranged beneath the cuticle, which is perforated in the centre of the mass to form an ostiole. No regular para- physes are produced but a few spermatial hyphae may elongate and project as sterile threads (fig. [68a). The spermatial hypha is a long, narrow cell with a central elongated nucleus. It is furnished at its free end with a ring of thickening which may be concerned with the disjunction of the spermatium. The development of the latter begins by the pushing out of a finger-like projection at the apex of the parent hypha. When it has attained its full size the nucleus of the hypha divides and one of the daughter nuclei enters the spermatium, which is cut off by a wall formed just above the thickened ring (fig. 169). The mature spermatium is a small more or less oval cell, enclosed in a very thin wall. The cytoplasm is finely granular with apparently no reserve material, and the nucleus is of relatively large size. When cultivated in solution of sugar or honey, spermatia have been induced to undergo a form of yeast-like budding, and this has been observed under natural conditions by Robinson in Puccinia Poarum. But, though many attempts have been made, it has so far proved impossible to bring about the formation of a mycelium. It seems, therefore, pretty clear that the spermatia are useless as agents of infection, and they differ also in structure from ordinary asexual spores. On the other hand the suggestion was long ago made that they may be male reproductive elements, and this is borne out by their large nuclei and lack of reserve material, and is by no means invalidated by the fact that they possess some slight power of germination. Recent investigation has shown that they are now no longer functional. As a rule considerable numbers of spermatia are to be found in various stages of degeneration scattered around the ostioles of the spermogonia. In some cases the spermatia are aggregated in sticky masses and appear to attract insects. The presence of sugars in the spermi>L,r<>nial contents has been demonstrated for species of I rromyces, Puccinia, Endophyllum, and Gymnosporangium; in some cases the spermogonia also possess a strong odour as in Puccinia suaveolens, or occur on bright spots which contrast with the green of the surrounding tissue. Such spots are usually yellow or orange, but are white in Uromyces Fabae and reddish-purple in Puccinia 200 PROTOBASIDIOMYCETES [ch. Phragmitis. A corresponding discoloration takes place around the young aecidia, and there is thus some suggestion that the spermatia, when functional, were carried to their destination by insects. The aecidia occur in groups, usually on the abaxial side of the leaf ; in them the aecidiospores are produced in basipetal rows (fig. I/O) alternating with small, abortive, intercalary cells, by the disintegration of which they are set free. They may be carried to consider- able distances by the wind, and there is evidence that they are sometimes distri- buted by means of insects or of snails. The mature aecidio- spore is usually subglobose or polygonal in form, it is enclosed in a thick wall per- forated byseveral germ-pores, and contains red, yellow or orange pigment, and always two nuclei. In germination a hypha is put out which enters the host plant through one of the stomata and so penetrates into the inter- cellular spaces. The development of the aecidium begins by the mass- ing of hyphae either deep in the tissues of the host (Gym- nosporangium clavariaeforme, Fig. 170. Uromyces Poae Raben.; aecidium just before "the epidermis is broken through, x 310; after Black- man and Fraser. Fig Uromyces Poae Raben. ; young aecidium, ■ 370; after Blackmail and Fraser. Puccinia Poarum (Blackmail and Fraser '06), Puccinia Falcariae (Ditt- schlag '10)), or directly below the epidermis (Phragmiditim violacaim ( Black- man '04), Uromyces Poae (Blackman and Fraser '06) (fig. 171), Puccinia Claytoniata (Fromrne '14)); these hyphae give rise to a more or less regular series of uninucleate cells. These are the fertile cells, but, before developing further, each, at any rate in the relatively primitive forms (caeomata), may cut off one or occasionally more terminal sterile cells which ultimately degenerate. The fertile cells may unite laterally in pairs (fig. 172), so that binucleate compound cells are formed ; they may similarly pair with the VIII] UREDINALES 20 1 Fig. 17:. Phragmidium speciosum Fr. ; a. fertile and sterile cells; b. fusion of two fertile cells; after Christman. 1 ells below them (Fromme '14), or each may receive a second nucleus by migration from a neighbouring vegetative cell (fig. 1751. In each case they now constitute the basal cells of the rows of spores and theyproceed at once to cutoff aecidiospore mother- cells, each of which in turn divides to separate a small intercalary cell below from the aecidiospore above. Exceptionally bi nucle- ate cells may be observed before the fertile layer is differentiated. In Puccinia Poarittn nuclear migrations sometimes take place be- tween the vegetative cells at the base of the very young aecidium. These cells may grow up, either at once or after division, to form fertile cells. The aecidiospores, then, are the products of asexual process by means of which two nuclei become associated within the limits of a single protoplasmic mass, form- ing the dikaryon or synkaryon of Maire. The nuclei thus brought together do not fuse, but undergo simultaneous division (fig. 174), so that a daughter nucleus, from each passes into even- new cell. Conjugate division is continued when the aecidiospore germinates and a mycelium of binucleate cells is produced. The sporophyte of the rusts is thus normally inaugurated in the fertile cells of the aecidium. It is not unusual to find spores and vegetative cells which contain three or more nuclei ; in these, as in the binucleate cells, and, indeed, in multinucleate cells of many different groups of plants, conjugate Fig. 1 ;.',. Phragmidium violaceum Wint.; migration of ei nil nucleus into fertile cell of caeoma, x 950 ; alter Blackmail. Fig. 174. Melampsora Roslrupi Wagn. ; paired fertile cells, x 1:00;, after Blackman and I- u er. 202 PROTOBASIDIOMYCETES [CH. division takes place (fig. 175). The origin of the trinucleate cell by the fusion of three fertile cells has been observed, and no doubt it may arise by the migration of a second vegetative nucleus. .,.;,0-viv^fe:. -J^d . Fig. 17;. Puccinia Poantm Niels. ; conjugate division, X2280; after Blackman and Fraser. At the periphery of the aecidium the cells cut off from the basal cells divide in the usual way, so that two cells corresponding respectively to the aecidiospore and the intercalary cell are formed from each. The upper (aecidiospore) cells acquire very thick striated walls, lose their content-, and form a sheath or pseudoperidium about the sporogenous part. The behaviour of the lower cells varies considerably ; Kurassanow has shown that in some cases they are quite small, like typical intercalary cells, while in others they are relatively well developed and form part of the pseudo- peridium. This is especially the case where the tissue to be broken through by the developing aecidium is dense or extensive. Centrally the pseudo- peridium arches over the contents of the aecidium. In this region it is derived from the cells first cut off by the central basal cells. These, like the others, divide transversely, and one of the daughter cells, usually the outer one, corresponding to the aecidiospore, becomes one of the elements of the pseudoperidium (Dittschlag, Kurassinow). When the aecidium reaches maturity the pseudoperidium pushes through the epidermis of the host and is then itself ruptured and exposes the ripe spores. It becomes torn and recurved so that the characteristic cluster-cup is produced (fig. 176). The pseudoperidium is sometimes much elongated and cylindrical or inflated, producing the forms known as roestelia (Gymnosporangium), and peri- dermium (Coleosporium, Cronartium and allied genera), so-called from their old generic names, or it may be represented only by a few paraphyses or altogether absent (Phragmidium, Melampsord). The latter forms, to which the term caeoma is applied, are probably primitive. In the majority of cases, after the fertile and sterile cells have been formed and nuclear association has taken place, the basal cells each give rise to a single chain of spores, but occasionally {Puccinia Falcariae (fig. 177), Endophyllum Sempervivi) they may branch and thus produce two or more spore-rows. In certain other species the basal cells regularly form a number of lateral buds or branches and each of these is cut off as a spore VIII] CKKDIXALKS ^03 r ig. 1 76. Puccinia Graminis Pers. ; a. infected leaf of Bcrberis vulgaris, nat. size: />. group of aecidia, x 5. Uromyccs Poat Kabenh.; c. infected leaf of Ranun ultis ficaria, nat. size; d. group of aecidia, x 20; E. J. Welsford del. mother-cell (fig. 178). The spore mother-cell divides in the usual way, separating the aecidiospore above from its sister-cell below, but the latter here forms an elongated stalk instead of an intercalary cell. Each outgrowth of the basal cell thus produces only a single spore, the mode of formation of which is exactly similar to that of a uredospore. The fructification has generally been regarded as a uredosorus and is known as the primary uredosorus, in reference to its appearance relatively early in the season. Fig- '77- Puccinia Falcariae; branched fertile cell of aecidium or primary uredosorus, x 1200: after Dittschlag. Fig. 1 ;*. Phragmidium Potcntillae-Canadensis Diet.; a. conjugation; /'. branched fertile cell ; after Christman. 204 PROTOBASIDIOMYCETES [CH. But the fact that these sori are developed on the same mycelium as the spermogonia, the fact that in their fertile cells nuclear association takes place and the fact that in the formation of the fertile cell a sterile cell is cut off, all suggest that the true homology is with the aecidium. The mycelium formed by the germination of the aecidiospore grows with renewed energy. It consists of binucleate cells giving rise to uredospores. These are borne in groups or uredosori (fig. 179) which may be surrounded Fig- >79- "• Phragmidium Rubi Pers.; uredosorus, x6oo; after Sappin-Trouffy; b. Phragmidium violaceum W int.; uredosorus, X480; after Blackman. by paraphyses, or in certain genera (Pucciniastrum, UrcJinopsis) by a pseudo- peridium. In the young sorus a regular layer of somewhat rectangular basal cells is formed, from which the uredospore mother-cells arise. In Colco- sporitim, in Chrysomyxa, and in the secondary caeomata of Phragmidium subcorlicium, they are produced in vertical rows like the typical aecidiospore mother-cells and divide to' form uredospores and intercalary cells, but, in the large majority of cases, they appear as a succession of buds from different parts of the basal cell. Each bud elongates, its nuclei undergo conjugate division, a stalk is cut off which grows in length but remains narrow, while the uredospore enlarges considerably, its contents acquire an orange or yellow colour, and its wall is variously roughened in most species by minute projections on the surface. Two or more germ-pores are usually present and the uredospore, like the cells which give rise to it, is invariably binucleate ; it produces a binucleate mycelium on which teleutospores or further crops of uredospores are formed. Certain species (Puccinia vexans,etc), occurring under very dry conditions, \ lit I L'RKDINALKS 205 produce a second type of uredospore with thick walls which arc adapted to survive unfavourable conditions; these are known as amphispores. Both aecidio- and uredospores germinate readily and without a rest if fully ripe, but many are shaken off by wind and rain before they reach maturity and remain incapable of germination. Moreover it is stated that spores will not ripen properly on leaves that have been removed from the plant. Sooner or later the mycelium of binucleate cells gives rise to teleuto- spores; these are characteristically grouped together in teleutosori (fig. 180), w-*—^^/- Fig. 180. a. Phragmidium Kuln Pers.; teleutosorus, x 240 : after Sappin-Trouffy ; b. Pkragmidium violaceum Wint.; teleutosorus, 240; after Blackmail. except in the genus Uredinopsis, on ferns, where they are scattered. Like the uredospores the teleutospores are with or without paraphyses and like them arise from rectangular basal cells. They appear as narrow binucleate outgrowths in which one or more divisions take place so that, in the majority of cases, a stalk is formed below and the simple or compound teleutospore is produced above (fig. 181). The stalk may increase consider- ably in length (Gymnosporangium, Uromyces, Puccinid) or may be very short or absent (Colcosporiuiu, Melampsord). As already stated tin; young teleutospore cell is binucleate (fig. [82); when the wall is fully thickened the two nuclei fuse and the spore passes into the resting state. On the renewal of its development two nuclear divisions occur and the gametophytic phase is initiated with the production of the uninucleate basidiospore. In the Uredinales the fertilization process thus takes place in two stag< . nucle tr association being separated by a longer or shorter series of vegetative cells from nuclear fusion. We have here a difference in degree though not 206 PROTOBASIDIOMYCETES [en. in kind from the normal process. In Pinus sylvestris1 the male and female nuclei lie side by side but do not fuse till their chromosomes become mingled on the first spindle of the embryo ; in many of the protozoa and in some other animals a series of conjugate divisions may precede the combination of the paternal and maternal chromosomes in a single membrane. Fij,'. 181. Puccinia Podophylli S.; fertile cell of teleutosorus giving risetoteleutospores; after Christ- man. Fig. 182. Pliraamidiitm violaceum Went.; a. teleuto- spores, x 1080; />. fusion of nuclei in teleutospore, x 1520; after Blackman. It may be hazarded that in the Uredinales the similarity of the physio- logical history of the nuclei before they become associated is responsible for a minimum of attraction between them, so that there is no sufficiently strong impulse towards fusion till meiosis is about to take place ; being, however, in the same cell, they have no opportunity of dissolving partnership and the influences which bring about meiosis affect both alike. A considerable similarity exists in the arrangement of the different groups of sporogenous cells. The uredo- and teleutosori are clearly com- parable, both are of indefinite extent, with or without a border of paraphyses, and both consist of groups of rectangular basal cells from which the spore mother-cells arise in horizontal series and divide to produce the simple or compound spore and the stalk-cell. Sometimes, however, the uredospores are borne in vertical series, one below the other, and the sister-cells of the spore form short, intercalary cells instead of stalk cells (fig. 183). This arrangement and that of the so-called primary uredospores link the uredosorus to the aecidium, suggesting the homology of the stalk and inter- calary cells. In the simplest aecidia, those of the caeoma type, we have a 1 Blackman, V. H., 1898, Phil. Trans. B. exc, p. 395 VIII] rUKDIXALKS 207 Fig. 183. Coleosporium Son- chi ; uredosorus, x 545 ; alter Holdenand Harper. group of basal cells of indefinite extent, from which the aecidiospore mother- cells are cut off. The aecidium is, in fact, no more a definite organ than the uredo- or teleutosorus, and only appears so in the more elaborate forms because of the modification of its peripheral cells to form a pseudoperidium. The important distinction lies not in the general morpho- of the sorus, but in the fact that an association of two nuclei from different cells takes place in the basal cell of the aecidium and in the specialization indicated by the separation of the sterile cells. In its general structure the spermogonium, con- Mating as it does of a series of spermatial hyphae with or without circumjacent paraphyses, is not very different from the other son', and, in the simplest < ases, it also is of indefinite extent. Omission of Spore Forms. In many rusts one < >r more spore forms arc omitted ; the case where the so-called primary uredospore is substituted for the typical aecidiospore has been already described ; these and others in which the characteristic aecidium or caeoma alone is lacking are distinguished by the prefix brachy. Hemi- indicates the presence of uredo- and teleutospores without aecidia or spermogonia. The suffix opsis is used for forms with aecidia and teleutosori. They lack uredosori but a few uredospores are sometimes found in the teleutosorus. Micro- and lepto- forms have teleutospores with a few occasional uredospores and sometimes spermogonia. The teleutospores germinate in the former group only after a period of rest, in the latter upon the same host plant as soon as they reach maturity. Species with the full complement of spores are distinguished by the prefix eu. As already pointed out, the sporophyte in some of the brachy- species starts from the fertile cells at the base of the so-called uredosorus, and this may very probably prove to be true in all cases where the ordinary aecidium is absent and spores developed like uredospores accompany the spermogonia. The alternation of generations in the -opsis forms is also normal, for these are characterized by the omission of typical uredosori the development of which is related tb no significant change in the nuclear life-history. In micro- and lepto- forms the basidiospore germinates to produce, as in at- species, a mycelium of uninucleate cells on which spermogonia may occasionally be borne. The mycelium becomes binucleate cither during vegetative development (Uromyces Scillarum, Puccinia Adoxac) or below the young teleutosorus, and the fusion in the teleutospore takes place in 208 PROTOBASIDIOMYCETES [ch. the usual way. In the micro- form Puccinia transformans Olive observed that the binucleate condition was brought about by the fusion in pairs of cells to form the basal cells from which the teleutospores arose and the same has been reported by Moreau for Puccinia Buxi and Uromyces Ficariae. In Puccinia Malvacearum Moreau occasionally found a difference in size between the fusing cells, and Werth and Ludwig observed the migration of the nucleus of the smaller cell into the larger (fig. 184^). Below the teleutosorus of Puccinia Podophylli also, Christman found nuclear migrations in progress (fig. 184^). Such cases clearly suggest that here, as in the mycelium below the aecidium of P. Poarum and in the prothallus of pseudapogamous ferns, the sporophyte is initiated by the association of two vegetative nuclei. Christman, however, observed that in certain cases migration took place between cells already binucleate, and he hence regards migrations in this case, and is inclined to regard all other migrations in rusts, as due to pathological causes. Fig. 1S4. Puccinia Malvacearum Mont.; a. conjugation Fig. 18;. Endophyllum Sen,. of unequal cells at base of teleutosorus; b. teleutospore ; Lev.; fertile cells and spores; after both after Werth and Ludwig. c. Puccinia Podophylli Hoffmann. S-; migrations at base of teleutosorus; after Christman. A sporophytic stage of exceptionally brief duration is also found in the species of Endophyllum and in the form on Rubus frondosus known as Kunkelia nitens1. In both cases the characteristic spores are developed in basipetal chains (fig. 185), and in both the fertile cells which give rise to them fuse in pairs (Olive '08; Hoffmann '1 1), so that the spore mother-cells, intercalary cells and spores receive two nuclei each. In Endophyllum the spores are enclosed in a pseudoperidium of barren cells so that the sorus appears as a typical aecidium, in Kunkelia nitens it is of simpler, indefinite 1 Kunkelia nitens (Schwein.) Arthur = Caeoma nitens Burr. VIII] UREDINALES 209 form; in both cases it is borne in association with spermogonia on a mycelium of uninucleate cells. Hut the spore germinates like a teleutospore Fig. 1 So . Endophyllum Sempervivi Lev.; spores giving rise to basidia; both after Hoffmann. (fig. 186); its two nuclei fuse (fig. 187), its contents are extruded as a pro- mycelium, two successive nuclear divisions occur, cross walls appear and four basidiosporcs are produced, which, in due course, give rise to a uninucleate mycelium. The sporophytic stage thus endures only from the fusion of the fertile cells until the germination of the spores which they produce. Incidentally these observations in the case of Kunkelia nitens have demonstrated that the caeoma of this fungus is not a stage in the life-history of the teleutospore-producing Puccinia Peckiana on the same host, for the mycelial cells of/'. Peckiana are binucleate and the teleutospores germinate in the usual way. The development of an apo- gamous aecidium has been ob- served by Moreau in a variety of Eiidopliyllitm Euphorbiae on Euphorbia sylvatica ; here the basal cells, aecidiospores and cells of the pseudoperidium are uninucleate throughout their development, the aecidiospore germinates to form a promy- Celium Of three or four cells Fi§- ,s7- Endophyllum ivi Lev.; a. nuclear fusion iii spore; b. synapsis in fusion nucleus; after and neither nuclear association Hoffmann. G.-V. '4 2io PROTOBASIDIOMYCETES [ch. nor nuclear fusion takes place at any stage, the diplophase being wholly omitted. Heteroecism. In many rusts the gametophytic and sporophytic mycelia occur on different host plants. Such forms are termed heteroecious in contrast to the autoecious species where the whole life-history is passed on a single host. It is not surprising that the different spore forms on such species were recognized and described some time before it was understood that they are stages in the life-history of a single fungus. The final proof of the relationship of the aecidia and spermogonia on the one hand and the uredo- and teleutosori on the other, was given by de Bary in 1865 for Puccinia Graminis, the wheat rust or, as the teleutospore stage was called by early investigators, the wheat mildew. In this plant the haplophase occurs on the leaves of the Barberry (Berberis vulgaris) and the diplophase on wheat, oats, rye and other grasses. Long, however, before this relationship was demonstrated, and even before the fungal nature of the disease was known, farmers had begun to suspect some malign connection between barberry bushes and their wheat crop, and had observed that dark areas of blackened and injured wheat were apt to occur in the neighbourhood of such plants. In the State of Massachusetts an act was passed requiring the inhabitants to extirpate all barberry bushes before a given date in 1760 and Marshall, of Norfolk, writing in 1781, says that "it has long been considered as one of the first of vulgar errors among husbandmen that the barberry plant has a pernicious quality (or rather a mysterious power) of blighting wheat which grows near it1." It is hardly to be wondered at that learned persons of the time repudiated this belief, or, as Marshall says of himself, "very fashionably laughed at it." It was not till 1797 that Persoon identified the wheat disease as a fungus and gave it the name it still bears. In 1805 Sir Joseph Banks called attention to its resemblance to the rust on the barberry, suggesting that it might be one and the same species, "and the seed transferred from the barberry to the corn." In 1 8 16 Schoeler, a Danish schoolmaster, set himself to deal with the matter experimentally, and applied rusted barberry leaves to some marked plants of rye ; after a few days these were badly affected while not one rusty plant could be found elsewhere in the field. His discovery was con- firmed by the investigations of de Bary, who performed the infection in both directions and under more critical conditions, and it has since been shown that a large proportion of the rusts are in fact heteroecious. It seems pretty evident that the autoecious condition must have been primitive and it would be of interest to know what factors determined the adoption of different hosts for the different phases of the life-history. 1 Rural Economy of Norfolk, 2nd ed. vol. ii, p. 19, London, 1795. vin] LJREDINALES 21 I Christman and Olive have inferred that the ancestral type of the heteroecious species was a form with teleutospores only, a lepto- or a micro- form occurring on the host of the present gametophyte. Other investigators (Tranzschel '04, Grove '13) who regard the aecidium as an essential constituent of the primitive rust, have suggested that hetcroecism may have arisen in relation to host plants with a short vegetative period. In such a case there would hardly be time for the production of the full complement of spores and the fungus might either sin >rtcn its elaborate life-histi iry.giving the micro- < >r simi- lar forms ( Uromyces Scillarum on wild hyacinth, Pucciniafuscaon anemone), or some of the spores might become adapted to life on a new host. This might be the case in particular with the aecidiospores, the development of which, owing perhaps to the recent fertilization stage, is especially vigorous. Aecidiospores must fall on hundreds of leaves besides those of the host, and the germ-tubes in their case enter through the stomata. If then an aecidiospore germinated and penetrated a satisfactory host it is suggested that a mycelium might develop and further adaptations might fix the heteroecious habit. Again it is readily understandable that the Gramineae and other hosts with similarly refractor)- cuticles are easily infected by the germ tubes from the aecidio- and uredospores which pass through the stomata but not by those of the basidiospores which, in a large majority of cases, penetrate the walls of the epidermal cells. This fact may be significant in relation to the return of the parasite to its gametophytic host each spring. There is reason to believe that some species have an autoecious and a heteroecious variety and the study of such forms is likely to prove of great assistance. Specialization of Parasitism. The parasitism of the rusts shows very marked specialization so that biological species have arisen, which, though they may be morphologically indistinguishable, differ from one another in their power to infect different hosts. Injury to the host may break down its resistance to attack and may render it liable to infection by a species to which it is normally immune. 1'nder favourable conditions rust appears suddenly, and spreads with great rapidity. Eriksson believed such epidemics to depend on the presence in the seeds or buds of the host plant of the protoplasm of the rust, indistinguishably mingled with that of the host, a mixture to which the term mycoplasm was applied. He considered that the protoplasm of the fungus remained unaltered till the leaves were formed ; under appropriate conditions it then separated itself rapidly from that of the host and developed into the ordinary spore-bearing mycelium. The investigations of Marshall Ward and others have not substantiated this hypothesis. Nuclear Division. It would appear, from the work of various observers, that nuclear division in the Uredinales has undergone a process of simpli- 14—2 212 PROTOBASIDIOMYCETES [ch. fication and in some cases it shows but few of the characters of normal mitosis. In the spermatial hyphae of Gymnosporangium clavariaeforme, for example, Blackmail has described a condensation of the nucleus to form a deeply staining body out of which the nucleolus is squeezed. The chromatin is drawn apart into two apparently homogeneous masses between which a kinoplasmic thread represents the spindle. A similar process takes place in the division of the conjugate nuclei in this and other forms, but the spindle is generally recognizable somewhat earlier, at a time when the chromatin of each nucleus still forms a single mass. As a rule the spindles of the conjugate nuclei lie parallel one to another (fig. 188). Moreau, following Sappin-Trourfy, has recorded two chromosomes or .,-.... chromatin masses formed from im. m tfe m Fig. i.SS. Urmnyces Poae Raben. ; conjugate divisions in aecidium, x 1330; after Blackmail and Fraser. each nucleus in various Uredi- neae. Olive on the other hand in Triphragmidium Ulmariae and Uromyces Scirpi has found a clearly defined spindle and centrosomes and has succeeded in recognizing several separate chromosomes ; a similar state of affairs has been recorded by Christman for Phragmidium speciosum so that it would ap- pear that the different species of rusts are at dissimilar levels in this matter, though a further study of carefully fixed material might be undertaken with ad- vantage. In all cases, however, the divisions of the fusion nucleus of the teleutospore are much more elaborate than those in the vegetative cells and show some of the characteristics of a meiotic In Coleosporium (fig. 189) the fusion nucleus at first possesses a well-marked reticulum of interlacing threads. This undergoes a stage of concentration in one part of the nuclear area, which no doubt corresponds to synapsis, and afterwards loosens out, increases in thickness and forms a spireme. The spireme breaks up and its segments are seen to be double throughout their length. In the meantime centrosomes and spindle fibres have appeared and characteristic gemini are recognizable on the spindle. Coleosporium Senecionis; mitosis in teleuto- spores ; after Arnaud. phase. VIII] URKDINALKS 213 Moreau describes only two, but I [arper and 1 [olden found a larger number, which became crowded together and more or less fused during the later stages of the first and also during the second division. In Gymnosporangium clavariaeforme ( fig. 190) the first divisii >n is initiated, as in Coleosporium, by a synaptic phase, after which a spireme is formed and breaks up into chromosomes. These pass on to the spindle M /.' \ ■'■'.. ,y but soon lose their individuality \ and travel in irregular masses to the poles. The development of the spindle has also been traced in this species ; its formation is extra-nuclear and it lies free in the cytoplasm before coming into relation with the dividing nucleus. This type is fairly common among animals but is of exceptional occurrence in plants. Nuclear Association. The cytology of the aecidium was first described in detail in 1904 In' Blackman, for Phragmidium vio/aceum, a species occurring on the bramble. The aecidium here is of the caeoma type, consisting of a group of fertile cells of indefinite extent and usually bounded at the periphery by a number of thin-walled paraphyses. Its formation begins by the massing of hyphae below the epidermis of the leaf where they form a series of uninucleate cells two or three layers thick. The cells next the epidermis increase in size and each divides by a transverse wall parallel to the surface of the leaf, separating an upper sterile cell from the fertile cell below. The sterile cells remain cubical and ultimately disintegrate; the fertile cells elongate to form a more or less regular layer and paired nuclei appear in them, first at the centre and later towards the periphery of the group (fig. 191 ). „. , , ... Fig. 191. Phragmidium vielaceum Went.; caeoma, The second nucleus in the ,,40: ,lMrl Blackman. Fig. 190. Gymnosporangium clavariaeforme Rees first division in basidium, x [460; after Blackman. 214 PROTOBASIDIOMYCETES [CH. fertile cells of Phragmidium violaceum was shown by Blackman and subse- quently by Welsford to be derived from one of the smaller cells at the base of the fertile layer. It is thus a vegetative nucleus; it enters the fertile cell by migrating through the wall, becoming much drawn out and laterally com- pressed. It leaves a pore which maybe identified after its passage (fig. 192). Fig. 19:. Phragmidium violaceum Went.; caeoma; a. migration of nucleus from vegetative cell of one hypha to fertile cell of another, x 1040; b. and c. binucleate cells showing the pore through which the second nucleus has passed, x 1010; after Welsford. After enterint Fig. iq.v Uro'iiyces Poae Kaben.; nuclear migra- tionsin young aecidiuni X950; after Blackman and Fraser. the fertile cell the second nucleus is at first smaller and denser than that originally present, but soon becomes similar to it in size and consistency. The fertile cell now elongates and in doing so pushes through and destroys the sterile cell above. The associated nuclei divide simultaneously, a transverse wall is formed between the pairs of daughter nuclei cutting off the aecidiospore mother-cell, and the process is several times repeated so that a row of cells is formed. Each of these divides again to separate a small, binucleate intercalary cell below from the binucleate aecidiospore above. A similar type of development initiated by the migration of a vegetative nucleus into the fertile cell, was observed by Blackman and Fraser in the aecidia of Puccinia Poarum and Uromyces Poae (fig. 193). But in neither of these was the sterile cell satisfactorily identified. In such cases it seems reasonably clear that the entrance of the second nucleus is not a primitive process but a form of reduced fertilization where a VIII] UREDINALKS 215 vegetative nucleus lias replaced that of the no longer functional male element. As already shown there is a strong presumption that this male element was the spermatium and the fertile cell may then be regarded as an oogonium and the young aecidium as a group or sorus of female reproductive organs. In this connection Blackmail has suggested a possible origin of the sterile cell ; in Phragmidium violaceum he found it to be occasionally elongated and pushed up between the cells of the epidermis so that it was covered only by the cuticle (fig. 194); if in the past it broke through this also, it would have formed an efficient trichogyne and may well have func- tioned as such. In the related species Phragmidium speciosum, Christman, in 1905, described a similar development of sterile and reproductive cells, but in this case the fertile cells become inclined one towards another in pairs and, at the point of contact, the walls dissolve so that the protoplasts come into relation, at first through a small pore, but later along the greater part of their length. Binucleate cells are thus formed (fig. 195), conjugate division Fig. 194. Phragmidium violaceum Went. ; caeoma; sterile cell pushing up between epidermal cells of host, x 1.500; after Blackman. Fig- '9S- Phragmidium speciosum Fr. ; fertile cells after conjugation ; aecidio- spore mother-cell above ; after Christ- man. takes place and aecidiospore mother-cells arc cut off so that a single row of aecidiospores is developed from each pair of gametes. Christman regards the fertile cells as isogametes between which conjugation takes place, and the sterile cells merely as buffers, of which the function is to assist in the rupture of the epidermis. His observations on Phragmidium speciosum were confirmed in 1906 by Blackman and Fraser for Melampsora Rostrupi on Mercurialis (fig. 174); these authors pointed out that the fusion of the fertile cells is a reduced fertilization, strictly comparable to that in Ph. violaceum but achieved by the union of female cells in pairs instead of by the entrance of a vegetative nucleus into the female cell. This interpretation is confirmed by the fact 216 PROTOBASIDIOMYCETES [CH. Fig. 196. Triphragmidium Ulmariae (Schum.) Link; primary uredosorus; condition intermediate between migra- tion and conjugation of fertile cell ; after Olive. that Moreau found both processes (cell-fusion being considerably more common than migration) in the same caeoma in Phragmidium subcorticium. Since 1905 nuclear association by the fusion of fertile cells in pairs has been observed in a number of species, and seems, according to our present knowledge, to be the usual method. In the primary uredosorus of Triphragmidium Ulmariae and in certain other species, Olive, in 1908, found arrangements of an intermediate type. Here the cells of the young fructification form a more or less regular layer and cut off sterile cells in the usual way. Other hyphae then push up among them, and cell fusion and nuclear association take place (fig. 196). Fusion begins through a narrow pore which afterwards broadens, and in many cases the nucleus of the younger cell migrates into the older one. The process is thus intermediate between those first observed by Blackman and Christman respectively, and the younger hvpha, which does not cut off a sterile cell, may be regarded as either a vegetative structure or a gametangium. Olive suggests that the migrations, recorded by Blackman and by Blackman and Fraser, may be merely early stages of a completer cell-fusion; the recent critical work of Welsford, however, nega- tives this hypothesis, nor would the occurrence of cell-fusion be of much importance once nuclear association had taken place. Phylogeny. The interpretation given to the processes which take place in the aecidium affects the conception of other spore-forms in the Uredinales and indeed of the phylogeny of the group. For Christman, the sporophyte arises by the conjugation of undifferen- tiated or scarcely differentiated isogametes which fuse to form the basal cells of the aecidium. The spermatia cannot on this interpretation be male organs, and he regards them as the once-functional asexual spores of the gametophyte. The basal cells of the aecidium are homologized with those of the uredo- and teleutosori, and the fact is emphasized that the basal cells of the primary uredosorus and sometimes of the teleutosorus also may arise by cell-fusions similar to those in the aecidium. Christman is inclined therefore to regard the micro- species, in which the only spore-forms are teleutospores, or teleutospores and spermatia, as the primitive rusts, and to see in them a gametophytic mycelium bearing asexual spores (spermatia) and undifferentiated gametes by the union of which the basal cells of the teleutosorus are produced. Outgrowths of these cells bear the teleutospores vni] UREDINALES 217 in the germination of which the sporophyte comes to an end and the new gametophyte is initiated. Intci this simple life-history the nredospore and aecidiospore are held to be afterwards successively inserted as extensions of the sporophytic phase. From such a point of view the rust might be related directly to the Phycomycetes or other simple forms. Blackmail's work, on the other hand, indicates that the spermatium is an abortive male element, the fertile cells of the aecidium are female organs which, in the absence of normal fertilization, either fuse in pairs or receive a vegetative nucleus by migration. In micro- forms the female organs have- disappeared and the abbreviated life-cycle, like that of the pseudapogamous ferns, shows the sporophyte initiated by an association of two vegetative nuclei. The eit- forms (or the -opsis forms with teleutospores, aecidiospores and spermatia), are therefore primitive and the forms with a shorter life- history are of secondary origin and reduced. The female organ consists of two cells, the upper of which may have functioned as a trichogyne. Comparing the two hypotheses it may be noted that Blackmail's has the advantage of correlating all the known facts, since the association of female nuclei in pairs and of female and vegetative nuclei are both observed methods of replacing normal fertilization. Christman, on the other hand, is obliged to ignore the migrations of vegetative nuclei, or to regard them as pathological. Even for this reason alone it would appear, in the present state of our knowledge, more probable that the Uredinales are a group in which the normal sexual process has disappeared, and is replaced by various forms of pseudapogamy. The young aecidia must then be regarded as groups of female organs, each consisting of a fertile and a sterile cell, and the sper- mogonia would appear to be corresponding groups of male organs, the spermatia or antheridia, with the filaments which bear them. A third suggestion proposes Endophyllum as a primitive form. The mycelium of uninucleate cells bears spermatia and cluster-cups. At the base of the cup fusion of fertile cells in pairs occurs, and spores and inter- calary cells are produced in chains. The spore germinates by the formation of a septate basidium on which four Imsidiospores are produced in E. Euphorbiae, but an irregular number, sometimes as many as eight from one cell, in E. Sempervivi. In Uromyces Cunninghamianus (on Jasiiiiiutiii) Barclay, in 1 So 1 , observed that the aecidiospore germinates by a tube in which one transverse wall is formed and the cells give rise to secondary hyphae which produce infection. On the resultant mycelium, spores similar in arrangement to aecidiospores are formed; so that here, as in Coleosporium, we have the accessory spores of the diplophase produced in chains. In the same sorus teleutospores, which are in this genus unicellular, may also arise. The cytology of this 218 PROTOBASIDIOMYCETES [ch. species has not been investigated, but there is an indication of a transition between Endopliyllum and the eu- forms It is postulated that the cells of the promycelium of an Endophyllum-Yiks. ancestor might have produced infection directly instead of by means of basidiospores. Nuclear fusion and meiosis would be postponed till the formation of teleutospores, which would arise as the typical spores of this new vegetative sporophyte. Later the teleutospore would become specialized as a resting spore and uredospores would take on the function of rapid propagation of the plant. But Endophylliim has a definite cluster-cup, and well-marked peridium, and is therefore not likely to be primitive, though it may point to an hypothetical primitive ancestor ; a species must rather be sought with a caeoma from the aecidiospores of which promycelia are produced. Such a form has been recognized in Kunkelia nitens. There remain to be considered the various forms of teleutospore. Presumably the unicellular type is more primitive than the multicellular. Simple teleutospores occur in Melampsora (where also the aecidiospores are developed in a caeoma), in Uromyces and in the Coleosporiaceae. In the last-named family meiosis and septation take place inside the teleuto- spore wall, but the elaboration of the other spore-forms forbids this group being regarded as primitive, though the internal basidium may be. It may be hazarded that the ancestral rust bore spermogonia or groups of male organs and groups of female organs of the caeoma type, that the individual male organ was an antheridium or spermatium set free from its parent hypha, that the female organ consisted of a fertile cell or oogonium and a sterile cell which was perhaps elongated to form a trichogyne reaching up to the surface of the host, and that the product of fertilization was a series of aecidiospores. It may further be suggested that either the aecidiospore germinated by giving rise at once to a promycelium or that an alternation of vegetative generations occurred and that the sporophyte bore simple teleutospores or tetrasporangia inside which septation took place. The members of the Uredinales may be arranged in four families : Germination by a promycelium (except in Chrysopsora) Teleutospores stalked Pucciniaceae. Teleutospores sessile arranged in series but separating later CRONARTIACEAE, one or many celled, loose in tissue of host or united in a flat layer under the epidermis MELAMPSORACEAE. Germination without a promycelium, formation of basi- dium internal ; teleutospores sessile or with a lateral pedicel COLEOSPORIACEAE. vin] UREDINALES 219 Pucciniaceae1. The teleutospores of the Pucciniaceae are provided with a stalk which is often well developed, but is in some cases short or becomes detached at an early stage (deciduous). The teleutospores are one-celled in Uromyces and Hemileia, two-celled in Puccinia and Gymnosporangium; they are made up of three cells in TripAragmidium, and in Phragmidium of three or more cells. Gymnosporangium is further characterized by the long pedicels of the teleutospores and the fact that they are imbedded in a gelatinous mass. The uredospores are solitary and the aecidiospores produced either in caeomata (TripAragmidium, Phragmidium), or in aecidia, which in Gymno- sporangium are commonly elongated to form flask-shaped or cylindrical roestelia. This family probably includes some of the most highly developed members of the Uredinales, but it includes also several species with caeo- mata, and one, Cluysopsora Gynoxidis, belonging to a monotypic genus in Ecuador, in which the two cells of the stalked teleutospore germinate by internal septation and the protrusion of sterigmata bearing basidiospores as in Coleosporium. Cronartiaceae In the Cronartiaceae the teleutospores are unicellular and sessile, so that they simulate multicellular spores. In Chrysomyxa they form waxy crusts, and in Cronartium a cylindrical body. A pseudoperidium is developed around the aecidiospores. The genus Endophyllum is sometimes placed here, sometimes a separate family, the Endophyllaceae, is constituted for it; it differs from the rest of the Cronartiaceae and from the majority of the rusts in the fact that its basidia are developed from spores resembling aecidiospores which arise in an aecidium-like sorus protected by a pseudoperidium. Melampsoraceae The teleutospores are sessile, loose in the tissue of the host in Uredi- nopsis, in the other members of the family grouped in a flat layer under the epidermis. In Melampsora and its immediate allies they are unicellular; in other genera they are divided either vertically into two cells or by cruciately arranged septa into four. The aecidiospores may be surrounded by a pseudoperidium or arranged in a caeoma; sometimes a pseudoperidium is present around the uredosorus also. 1 For Bibliography of this and other families, see the end of the group. 22o PROTOBASIDIOMYCETES [ch. Coleosporiaceae The outstanding character of the Coleosporiaceae is the method of germination of the unicellular teleutospore which undergoes septation directly and, in Coleosporium and Ochropsora, without the protrusion of a pro- mycelium ; in Zaghouania the contents of the teleutospore divide within the teleutospore-wall to form four cells, but emerge before the basidiospores appear. The aecidia are cup-shaped in Ochropsora, but in Coleosporium and Zaghouania they are of the peridermium type with a cylindrical, more or less inflated peridium ; this elaborate type of aecidial sorus makes it impossible to regard the family as primitive though it may perhaps have branched off early from the line leading to the commoner type of rust. UREDINALES: BIBLIOGRAPHY 1889 Plowright, C. B. A Monograph of the British Uredineae and Ustilagineae. Kegan Paul, Trench & Co., London. 1891 Barclay, A. On the Life history of a remarkable Uredine on Jasminum grandi- florum. Trans. Linn. Soc. Bot. ii, p. 141. 1895 POIRAULT, G. arid Raciborski, M. Sur les noyaux des Uredinees. Journ. de Bot. ix, pp. 318 and 381. 1896 Sappin-Trouffy, P. Recherches histologiques sur la famille des Ure'dine'es. Le Botaniste, v, p. 59. 1902 DUMEE, P. and MAIRE, R. Remarques sur le Zaghouania Phyllyfeae, Pat. Bull. Soc. Myc. France, xviii, p. 17. 1903 HOLDEN, R. J. and HARPER, R. A. Nuclear Divisions and Nuclear Fusion in Coleosporium Sonchi-arvensis, Lev. Trans. Wisconsin Acad. Sci., Arts and Letters, xiv, pt. i, p. 63. 1904 Bi.ackman, V. H. On the Fertilization, Alternation of Generations and general Cytology of the Uredineae. Ann. Bot. xviii, p. 323. 1904 TRANZSCHEL, W. Ueberdie Moglichkeit die Biologie wertwechselnder Rostpilze auf Grund morphologischer Merkmale vorauszusehen. Arb. Kais. Petersburg Naturf. Gesell. xxxv, p. 1. 1905 Chkim max, A. H. Sexual Reproduction in the Rusts. Bot. Gaz. xxxix, p. 267. 1905 Eriksson, J. On the Vegetative Life of some Uredineae. Ann. Bot. xix, p. 53. 1905 Ward, H. Marshall. Recent Researches on the Parasitism of Fungi. Ann. Bot. xix, p. 1. 1906 BLACKMAN, V. H. and Fraser, H. C I. Further Studies on the Sexuality of the Uredineae. Ann. Bot. xx, p. 35. 1906 McALPINE, D. The Rusts of Australia. J. Kemp, Melbourne. 1907 Christman, A. H. The Nature and Development of the Primary Uredospore. Trans. Wisconsin Acad. Sci. xv, p. 517. 1907 CHRISTMAN, A. H. Alternation of Generations and the Morphology of the Spore- forms in Rusts. Bot. Gaz. xliv, p. 81. 190S Olive, E. W. Sexual Cell-Fusions and Vegetative Nuclear Divisions in the Rusts. Ann. Bot. xxii, p. 331. 1910 Dittschlag, E. Zur Kenntnis der Kernverhaltnisse von Puuinia Falcariae. Centralbl. f. Bakt. Abt. ii, B. 28. viii| UREDINALES 221 191 1 Hoffmann, A. W. 1 1. Zur Entw ickelungsgeschichte von Endophyllum Sempervivi. Centralbl. fiir Bakt. Parasit. Infect, \xxii, p. 137. 1911 MAIRE, R. La Biologic des Uredinales. Prog. Rci Bot. iv, p. 109. 191 1 Olive, E. W. Origin of Heteroecism in Rusts. Phytopathology i, p. 139. 191 1 Sharp, L. \V. Nuclear Phenomena in Puccinia Podophylli. Hot. ('.a/, li, p. 463. 1912 FROM ME, F. I). Sexual Fusions and Spore Development of the Flax Rust. Bull. Torrey Hot. Club, xxxix, p. 113. 1912 RAMSBOTTOM, J. Some Notes on the History of the Classification of the Uredinales with full list of British Uredinales. Brit. Myc. Sir. iv, p. 77. 1912 WERTH, E. and LUDWIG, K. Zur Sporenhildung bei Rost- und Brandpilzen. Ber. deutsch. Bot. C.es. ,\xx, p. 522. 1913 Arnaud, G. I. a Mitose chez Capnodium meridionale zt chez Coleosporium Sen, cionis. Bull. Soc. Myc. de France, xxix, p. 345. 1913 GROVE, W. B. The British Rust Fungi. Camb. Univ. Press. 1913 GROVE, W. B. The Evolution of the Higher Uredineae. New I'hyt. xii, p. 89. 1914 FROMME, F. D. The Morphology and Cytology of the Aecidium Cup. Bot. Gaz. Iviii, p. 1. 1914 KUNKEL, L. O. Nuclear Behaviour in the promycelia of Caeoma nitens, Burrill, and Puccinia Peckiana Howe. Am. Journ. Bot. i, p. 37. 1914 KURASSANOW, L. Uber die Peridienentwicklung ini Aecidium. Ber. deutsch. Bot. Ges. xxxii, p. 317. 1914 MOREAU, MmeF. Les phenomenes dela sexualite chez les Uredinees. Le Botaniste, xiii, p. 145. 191 5 Welsford, E. J. Nuclear Migrations in Phragmidium violaceum. Ann. Bot. xxix, P- 293- 1916 Kunkel, L. O. Further Studies on the orange rusts of Rubas in the United States. Bull. Torrey Bot. Club, xliii, p. 559. 1917 ARTHUR, J. C. Orange Rusts of Rubus. Bot. Gaz. Ixiii, p. 501. GENERAL BIBLIOGRAPHY 1861 Tulasne, R. C. and L. Fungi Hypogaei. Klincksieck, Paris. 1861-5 TULASNE, R. C. and L. Selecta Fungorum Carpologia. Imperial. Typography Paris. 1882-1913 SACCARDO, P. A. Sylloge Fungorum. Published by the author. Padua. 1884 DE BARY, A. Comparative Morphology and Biology of the Fungi, Mycetozoa and Bacteria. Eng. Trans. 1887. Clarendon Press, Oxford. 1884-97 RABENHORST, L. Kryptogamen Flora. Pilze, by G. WINTER and E. FISCHER. Ed. Krummer, Leipzig. 1887 Phillips, W. A Manual of British Discomycetes. Kegan Paul, Trench & Co., London. 1892 von Tavel, F. Vergleichende Morphologie der Pilze. Fischer, Jena. 1892-5 Massee, G. British Fungus Flora. Bell & Sons, London. 1895 von Tubeuf, K. F. Diseases of Plants. Eng. Trans., 1897. Longmans, Green & Co., London. 1897-1900 Engler, A. and Prantl, K. Die natiirlichen Pflanzenfamilien. Fungi, by J. Schroter, G. Lindau, E. Fischer and P. Dietel. Engelmann, Leipzig. 1904-11 BOUDIER, E. Icones Mycologicae. Klincksieck, Paris. 1906 Massee, G. A Text Book of Fungi. Duckworth & Co., London. 1909 BULLER, A. H. R. Researches on Fungi. Longmans, Green & Co., London. 1909 Swanton, E. W. Fungi and How to Know Them. Methuen, London. 1910 Duggar, B. M. Fungous Diseases of Plants. Ginn & Co., New York. 1913 Massee, G. Mildews, Rusts and Smuts. Dulau & Co., London. 1913 STEVENS, F. L. The Fungi which cause Plant Disease. Macmillan Co., New York. 1918 BUTLER, E. J. Fungi and the Diseases of Plants. Thacker, Spink & Co., Calcutta. 1918 Harshbf.RGER, J. \Y. A Textbook of Mycology and Plant Pathology. J. & A. Churchill, London. 1919 HlLEY, \V. E. The Fungal Diseases of the Common Larch. Clarendon Press, Oxford. INDEX l ' . 118 (Fit;. 78) A. perplex, 111 . 9 A. Winteri, 10, 117 (Fig. 77) Ascocarp, 38. 39, 50, 55, 66, 71, 77. 95, no, 113, II9, 120, r2l, 123, 131, I35, I3S. [39, 142. '.59 Ascocorticiaceae, 93 Ascocorticium, 93 Ascodesmis, 50, 51, 52, 54. 98, 101 A. nigricans, 34, 9* (Fig. 56), 101 (Fig. 59), 102 (Fig. 60) Ascogenic cells, 176 Ascogcnous li \ j 1I1.1 . ■ . 39, 40, 43, 46, 47, .-.;, 56, 66, 69, 75, 86, 88, 98, 10''. 11.;, 114, 117 Ascogonium, 39; and see oogonium A si ycetes, 5, 6, 7, 8, 30, 34 et sqq. Ascophanus carneus, 9, 21, 46, 47 (Fig. 16), 48, 51, 118, 119 (Figs. 80, 81) .-/. equinus, 21 . /. ochraceus, 1 20 Ascophore, 38, 1 29 Ascospore, 3, 34, Si, 64, 79, 149 Ascus, 3. 34. 35 et seq., 41 et seq., 58 et fi , 89, 92,93, 95, 115, 177 Aspergillaceae, .-2, =4. 55, 57, 68 '. inierruptus, 24 ft. mollis, 24, 2; B. racemosus, 24, 25 B. sccali nus, 24 B. velutinus, 24 Brooks, F. T., 164 Brooks, W. E. St J., see Fraser and Brooks Brown, W. , 13, 20 Brown, W. H., ioj, 107, 116 132 Bryophyta, 161 Buchanan, J., 127 Bucholtz, F., 97, 137, 138 Budding, 5, 60, 62, 93, i8j, 199 Builliard, P., 40 Bulgaria polymorpha, 3;, 125 Buller, A. H. R.. 1:, 13, 31. 32, 33, 222 Bunts, see Ustilaginales Burgeff, II.. 17. 20 Butler, E. J., 2:2 Caeoma, 201, 202. 213, 2 14. 215 Caeoma nit ens (see Kunkelia nitcns) " Californian bees," 1 1 Ciil.it iia vulgarisi 16 Calosphacna, [6j C. princeps, [65 Capnodium, 12 Carruthers, IX. 43, 44, 48, 130 Caryophyllaceae, 21, 191 Cattleyeae, 17 Cavara, F. , 101 Cavers, F., 20 Celidiaceae, 100, 124 Celidium various, 125 Cell-fusion, 215, 216 Cenangiaceae, 100, 124 Central body, 88 Ceratomyces restrains, 173 (Fig. 134) Ceratomycetaceae, 180 Ceratostoma brevirostre (see Melanospora Zobelii) Ceratostomataceae, 154, 159 Cercospora, 163 Chaetomiaceae, 154, 155 et seq. Ckaetoiniuin chlorinitiii, 155 C.fimete, 54, 15.S C. Kuntzeanutn 35 (Fig. 2), 155 (Fig. 113), i.sn (Fig. u4) C. pannosum Wallr., 155 (Fig. 112) C. spirale, 1 40, 155 Chambers, H. S., see Fraser and Chambers Chemotropism, 14, 27, 186 Cherry-leaf-scorch, 163 Chlaviydococcus pluvialis, 3 1 Chlamydospore, 4, 57 Choiromyces maeandriformis , 137 Christman, A. H., 201, 203, 206, 208, 210, 212, 215, 216, 217, 220 Chromatin, 44, 45, 94 Chromosome association, 45, 113 Chromosomes, 43, 44 (Fig. 13), 89, 106, 109, 112, 113, 114 (Fig. 71), 115 (Figs. 72-4), 117, 130, 164, 179, 180, 212 Ckrysomyxa, 204, 219 C. Ledi, 23 C. Rhododendri, 23 Chrysopsora, 198, 21S C. Gynoxidis, 2 1 9 Chytridium vorax, 31 Cidaris, 1 29 ( lamp-connections, 1 ( 'lark, J. F., 27, 33 ifii iti in -I Fungi, 5 Claussen, P., 43, 46,98, 101, 102, 104, 105, 107 Clavate paraphyses, 38 Claviceps purpurea, 10, 21, 151 I < lenogamete, 2 Coleophora laxu < lla, 1 2 3 Coleoptera, 171 Coleosporiaceae, 218, 220 Coleosporium, 19K, 204, 212, 220 C. Serucionis, 2 1 2 (Fig. 1 89) C. Sonchi, 196 (Fig. 164), 207 (Fig. 183) C. Sonchi-arvensis (see C. Sonchi) Coleroa Potent iliac , 1 58 (Fig. 1 [8) Collema pulposum, ;i, 52 Colletotriclutm l.indcmuthianitm, 14 Compsomyees verticillatus, 176 (Fig. 137) Conidiophores, 4, 70, 72, 80 Conidium. 4, 1,;, 24, 57, 58, 60 (Fig. 21), 70, 72 (Fig. 31). 74, 79. So' Ilg. "5. !33. 14,:. 149. 1,-1, 161, i66, 170, 185, 186, 194 Conjugate division, 46, 177, 186, 201, 202, 204, 206 Conjugation, 59, 63. 1S6, 189. 190, 194, 208 Coprinvs, 9 ( . curtus, 31 C. niveus, 31 C. s/eri/itilinus, 9 Coprophilous Fungi, 8, 108, 112, 116, 156 Cordyccps, 10, 149 C. Barnesii, 151 (Fig. 111) C. capita/a, 151 C. militaris, isOjFig. no) C. ophioglossoides, 34, 150 (Fig. no), i = i C. sinensis, 149 Coremium, 4 Coreomyces, 174 Cortinarius, 19 INDEX 225 • I25 (,'. sarcoides, 1 25 liaceae, : is. 219 Cronartium, 119 C. asclipiadettm, 197 (F'ig- 165) itVrnt-, :i Ctnion 1 us, 67 (Fig. 27 1 Cutting, E. M., 9. 1.;, 4N. 119, 1;; /. 18 ■ ' • C. Candidas, 15, : 1 ogy of the Ascomycet.es, 40 . of the Uslilaginales, 187 . , tandestina, 21 D. Willkommii, 123 Dawson, M., 32, 33, 166, 169, 170 ryomyces globosus, 64 I lehiscence ol ascus, 36 - graphy, 68 Gymnoascus, 53, 54, 66 (Fig. 26) G. Candidas, 67 (Fig. 27) G. Reesii, 21, 66, 67 (Fig. 27) Gymnoconia interslitialis, 208 Gymnosporangium, 219 G. claim ia< forme Rees, 198 (Figs. 167, 16S), 199 (Fig. 169), 200, 212, 213 (Fig. 190) Gyromitra, 1 29 Hall, A. D., 13 Hall, J. G., see Stevens and Hall Hansen, E. C, 65 Haplophase or haploid phase, 3 Harper, R. A., 41, 42, 43, 45, 47, 48, 49. 82, 85, 86, 87, 88, 89, 104, 105, 106, 107, 117, 1 ::, 185, 186, 191, 192, 195 and Holden, R. J. ; see Holden and Harper Harshherger, J. W., 222 Hartig, R., 159 Hasselbring, H., ^^ Haustorium, 15, 79, 80 Heliotropism, see phototropism Helotiaceae, 97, 100, 122 et seq. Helotium, 123 Helvetia . 129 //. crispa, 2, 43, 44 (Fig. 12), 48, 129, 1 ;o (Fig. 90) //. elastica, 43, I2g Helvellaceae, 97, 127, I2g et seq. Helvellales, 6, 32, 36, 99, 127 Hemibasidiomycetes, 6, 183, 1841/^,7. ffemiieia, 219 Hemi-parasite, 6 Hemi-saprophyte, 6, 13 Hendersonia, 163 Heieroecism. 22, 210 Higgins, B. B., 160 Highley, 1'., 108 Hiley, W. E., 22 2 Hoffmann, A. W. H , 20S, 209, 220 Hofmeister, W. , 32, 33 Holden, R. J., and Harper, R. A., 207, 213, 220 Hop mildew, 84 Hornia, 1 H -piece, 1 Humaria carbonigena, 1 1 5 H. granulala, 48, so, ill (Fig. 67), 112 (Fig. 68), .13 H. Roumegueri, 1 [5 H. rutilans, 36 (Fig. 3), 41 (Fig 8), 43 (Figs. 10. 11), 44. 47, 4S. 49 (Fig. 17), 96 (Fig. 53). "3 (Fig. 69), 114 (bigs. 70, 71), 115 (Figs. 72-74) Hyaline cell, 4 Hydnaceae, 33 Hydnum, 2 1 Hydrotropism, 14, 29 INDEX 227 Hymenial layer, 36. 96 Hymeniuin, 3, ;v, 95. 136, 137, 139 Hymenogasteraceae, 8, 19 1 [ymenomycetes, 6, 35 Hypertrophy, 15, 16, 91, 1*4. 196 Hypha, 1, 41. ;f>. 58,60, 91,95, 101. 10.;, io'>. I !'). I46, I''.'. [67, [99 Hyphomycetes, 7; ami see Fungi itnperfecti knits, 17 • ' -i°- '.:'' ffypocrca, 149 Hypocreaceae, 14^, 146 ■/ ..,,/.: bibliography, 152 . 6, 140. 142, 143 1 [ypodermataceae, 134 Hypogeal fungi, 8. 77. 135 Hypomyces aurantius, [43 ff. lateritus, 140. 14,*, I [ypolhecium, 95 Hyp 1 •rum, 166 (Fig. 123) Hysteriaceae, 134 Hysteriales, 6, 96, 100, 133 [keno, S-, 75, 76, 94 Inordinate spores, 36 I alary cells (Uredinales), 86, 200, 202 Isaria, 150 Johannesberg yeasl II. 63 (Fig. 24 1. 65 Johnson, E. ( '.. see Freeman and Johnson Jolivette, II. D. M.. 30, 33 Juel, H. O., 61 Kenipton, F. E., 1 Kephir, 1 [ Kidston, K., and Lang. W. H.. 1 Kienitz-Gerloff, F.. 17: Kihlman, 0., 10;, 107. 144. 146 Klocker, A.. 62, 65, 73, 76 and Schionning, FL. 12 Knowles, ¥.. L., 94 Kny, L., 32, 33 Konokotine, A. G., siv Nadson and Konokotine Koumiss, 12 Kunkel, L. O., 221 Ktiiikclia nitetts, 208, 209. 21S Kurassanow, L., 202, 221 Kusano, S. , 18, 20 Kuyper, H. I'.. 7;, 76 Labiatae, 18 Lahoulbenia, 46. 171 L. chactophora, 171 (Pig. 131), 178. 1S0 (Fig. L. elongata, 172 (Fig. 132) /.. Gyrinidarum, \ -^ L. mflata, 1 77 /.. triordinata, 171 (Fig. 130) Laboulbeniaceae, 180 Laboulbeniales, 6, 15, 35, 51, 52, 54, 14:. 171 et sqq.; bibliography, 182 Lachnea cretea, 27. 51, 52, 109. 110 (Fig. 66) L. scutellata, 109 L. stercorea, 9, 39 (Fig. 7), 48, 49, 50. 52. 95 (Fig- .-2). 108 (Fig. 65) ■ . [9 Lagerheim, G. de, 61 Lanceolate paraphyses, 38 Lang, W. II.. 20 — — and Kidston, K. ; stc Ki.Kii>n and Lang Larch canker, 1 23 Larch ninth. 1 13 Lentinu . 7, 31 Leolia lubrica, 1 ;i (Fig. 91), 1 ',2 I kin, W. W.,65 1 l I I, I ''2 /.. Lemaneac, 162 (Figs. 1:1, 1221 Levine, M. N.. see Stakman, Piemeisel, and Levine Lewton-Brain, I... 34, 151, 152 Lichens, 52. [61, 181 Light, formative influence of, 31 Liliace Lindau, t ',., 222 Lophiostomataceae, 154. 160 iermium Pinastri, 134 Ludwig, K.. Werth and Ludwig Lutman, B. S., 186, 1N9. 172, 193, 194, 195 Lychnis alba, i-. 195 M Beth, I. G., and Scales. F. M., 13 McCubbin, \V. A., 43, 130 Maire, K. , 42, 43, 44, 114. 116, 130, 143, 201, 220 Ma • .'. 22 Marattiaceae, 18, 19 Marchal, E., 23. 26 Marchand, H., 66 Marchantia, 4 Marryat, I>. C. E., 25, 27 Marshall, W., 210 Massee, (',., 20. 26, 51, ;4. 97, 131, 132. [35, [38, 146, [51, 1 = 2. 222 and Salmon, L. S.. 9, [2, [58 Massee, L, 191, 195 Mayr, II.. 146 Meiosis, 3, 43. 53, 209. 212 Melampsora, 218, 219 .1/. belutina, 197 (Fig. 166) M. Rostrupi, 201 (Fig. 174), 215 Melampsoraceae, 218, 219 Melanospora, 144 M. damnosa, 144 Af. parasitica, 144 M. Zobelii, 144 Melhus, I. 1... 20 Meliola . 1 2 .!/. Pensigi, 90 us lacryman . 7 \l> - ispore, 197 Microspha ra, 82. 83 (1 ig. 40) .)/. Alni, Si, 88 ■poron furfur, 4 Microthyriaceae, 78, 79, 91 Migration, nuclear, 4S. 114, 186, 201, 208, 214 Mildew, white, see Erysiphaceae Mitrula laricina, 37 (Fig. 4I. 96 (Fig. 54) Miyabe Kingo, 163 hi, M., 14. 20. 2.y. 32, 33 Molliard, M., 9, 1 2 Mollisiaceae, 100, 122 et seq. 228 INDEX Monascus, 46, 74 M. Barken, 74 (Fig. 34) M. heterosporus, 10, 68 M. purpureas, 75 (Fig. 35) M.X., 75 (Fig. 35) Monilia, 124 M. albicans, 4 AT. iSclerotinia) cinerea, 22 Monoblepharis, 2 Monotropa Hypopitys, 19 Monoxeny, 21 Morchella. 129 .1/ eseulenta, 44, 130 J/, vulgaris, 130 (Fig. 90) Moreau, F., 146 Moreau, Mme F., 208, 209, 212, 213, 216, 22 r Mucor, 9. 10, 27, 32 M. Mucedo, 27, 29, 32 M, racemosus, 1 2 /)/. sloluni/er (see Rhizopus nigricans) Mucoraceae, 7 Mucorales, 5, 22, 30 Muriform spore, 4. 34 Mycelium. 1, [5, 17, 18, 34, 58, 79, 91, 103, 189, 100, 192. 194, 196. 197 My ooplasm, 211 Mycorhiza, 16 et sqq. Mycosphaerella nigerrislignia, 160 Mycosphaerellaceae, [54, 160 Nadson, C. A., and Konokotine, A. G., 66 Nectria, 19, 145 N. cinnabarina, 14. 14,- I Fig- 105) Nectriaceae, [43 el set/.; bibliography, 146 Neger, F. W., 89 Nichols, M. A., 47, 142, 144, 146, 159, 160 Nienbu'g. \V.. 147, 14S, 152 Non-motile spore, 4 Nuclear association, 46, 205, 206, 213, 214 Nuclear division (Uredinales), 211 Nuclear fusion, 45 el sqq., 48, 59, 60, S6. 87, toi, 105, 109, 121, 129, 149, 177, [88 el sqq., 206 el sqq. Nuclear migration, 48, 114, 186, 201, 208, 214 Nuclei, paired, 42, 46, 47, 60, 75, 177, 186, 201 Oak mildew, 81 Obligate parasite, 6, 14 Ochropsora, 19*, 220 Odonlogiossnm , 1 7 ( Hdiopsis tanriea, 80 Oidium, 4, 57, 58, 80 Oidium, 80 O. Qitercinutn, 81 0- Tuckeri, 80 Olive, K. W., 76, 20S. :io, 212, 216, 220 Oliver. F. VY.. 19 Olpidmm, 15 Oltmanns, F., 155, 156 Onyeena equina, 21,76 Onygenaceae, 57, 76 el sqq. Oogonial region, 39, 119 Oogonium, 2, 39, 4.1, 51, 52, .-4. 67, 71, 74, 75, 84, 85,87,98, 101, 103, 112, 176, 180. 215, 218 Oomycetes, 5 Ophioglossaceae, 18 Ort hcomyces, 17 Osmotropism, 30 Ostiole, 38 Otidea auran/ia, 95 (Fig. 51), 1 1 5 Otomycosis aspergillana, 20 Overton, J. B., 120, 121, 122 Page, W., 155 Paraphyses, 3, 36, 37, 38 Parasite, 6 facultative. 13 obligate, 14 Parasitism, 6, 13 et sqq.; bibliography, 19; specialization of, 20 el sqq. (bibliography, 26), 21 1 Parr, R., 30, 33 Palellariaceae, 96, 100, 124 Penicillium, 7. 10, 72 P. crustaceum (see P. glaucum) P. glaacnm, 12, 20, 31, 72 (Figs. 31, 32) P. vermititlalHin, 73 (Fig. 33) P. Wortmanni, 73 Peniston, A., sec Wagner and Peniston Peridermium, 202 Peridium, 38, 39 Periphyses, 38, 140 Perispoi iaceae, 79, 90 I', tiihecium, 38, 68, 81, 82, 83, 86, 87. 88, 90, 91, 137. 145, 148, 151, 154, 156, [57, [58, 162, 169. 171, 175 Pt ronospora Euphorbiae, 21 P. parasitica, 31 Pe osporales, g Persoon, C. H., 210 Peyritschiellaceae, 180 Peziza rutilans (see Hnmaria rutilans) P. lector ia, 1 1 5 P. theleboloides, 1 15 P. vesiculosa, 41, 49, 115 Pezizaceae, 50, 52, 100, 107 et sqq., 144; biblio- graphy, 1 if> Pezizales, 6, $6, 96, 97. 99, 100 et sqq. 1'ferTer, W., i> Phacidiaceae, 133 Phacidiales, 6, 96, 100, 132 et seq. Phillips, W., 222 Phoma, 1, 16, 163 Phototaxis, 31 Phototropism, 14, 30 midium, 197, 199, 202, 219 /'. bulbosuiu, 196 (Fig. 164) P. Potentillae-Canadensis, 203 (Fig. 178) /'. Rubi, 204 (Fig 179), 205 (Fig. [80) /'. speciosum, 201 (Fig. 172), 212, 215 (Fig. 195) P. subcorlicium, 204, 216 P. violaceum, 198 (Fig. 168), 200, 201 (Fig. 173), 204 (Fig. 179), 205 (Fig. 180), 20', (Fig. 182), 213 (Fig. 191), 214 (Fig. H121. 215 (F'g- >94) Phycomyces, 32 Phycomvcetes, 5 Phyllactinia, 35, 45, 82, 83, 87 P. Cory/ea, 21, 45 (Fig. 14), 79, 80, 83 (Fig. 40), 87 (Fig. 44), 88 (Figs. 45, 46). 89 (Fig- 47) INDEX 229 Phyllosticla, 32 Phytogeny, 49 et sqq., 03, et sqq., 140. 180, 188, 2 16 Phytophtkora infestans, 21 Piemeisel, F. J., r« Stakman, Piemeisel, and Levine Pilaere faginea, 2 1 Pihbolus, 8, 9, 10, 30 Piniu 1 .1 ,',4. 206 Piptocephalis Frestniana, 2 1 Plectascales, ft. 56 1/ <././., 181 Plectomycetes, 6, 53, 53- 55 *' •>' i/olii, 1 2 3 Psilotaceae, 18 Pteridophyta, 18, 91, [61, 196 /'v, -inia, 219 /'. Adoxae, 207 /'. Ami, 208 y. Caricis, 196 /'. Claytoniata, 200 /'. dispersa, 15, 13 /'. Falcariae, 200, 202, 203 (Fig. 1771 /'. fusca, 2 1 1 y. glumarum, 25 /'. Graminis, 2,;. 26, 203 (Fig. 176), 210 /'. Mahiacearum, 2:. 29, 31, 208 (Fig. 184) /'//. 1 i'»/a (1 (j///. ) /'. Peckiana, 209 /'. Phragmitis, 200 /'. Poarum, 31, 199, 200, 201, 202 (Fig. 17.-1. 20S. 214 /'. Podophylli, 206 (Fig. [81), 208 (Fig. [84) /'. suaveolens, 199 /'. transformans, 20S /'. itexans, 104 Pucciniaceae, 2 1 N, 219 /'//., iniastrum, 204 Culling. 36, [27 /'lira, 61 Pycnidium, 1. 4 Pj renomycetes, 6, 47. 50. 51, =2. 139 et sqq., 181 Pyronema, 50, gi, ,-2, 102 /'. confluens 21, 40, 42, 43, 44, 46 I Fig. 15I. 98 (Fig. 57), 102. 103 (Fig. 61), 104 (Fig. 62), 105 (Fig. 63), 106 dig. n4) y. oniphalotdes (see /'. confluent) Pyronemaceae, 100, 101 <•/ ."/(/.; bibliography, 107 Pythium, 19 /'. «t' Baryanum, 27 Rabenhorst, L., 222 Raciborski, M., 45 and Poirault, G.; >< , Poirault and Raci- borski Ramlow, G., 9, 13, 46, 47, 118, 119, 121, 122 Ranisbottom, ]., 9. 20, 62, 221 Ranunculaceae, 18 Ranunculus ficaria, 203 (Fig. 176) Rawitscher, F., 187, 18S, 189, iyo, 191, 193, 194. 195 Rayner, M. C, 16, 20 Reactions to stimuli, 27 et sqq.; bibliography, 33 Rei eptacle, 171, 175 Red Algae, 49, 50, 162, 172, 173, 181 Reproduction, sexual, 2; and see conjugation, fertilization, pseudapogamy ; non-sexual, 4; and see ascospore, b'asidiospore, conidium Reticulate spore. 5 Rhizma, 52, 128 R inflata, 128 R. undulata, 51, 128 Rhizinaceae, 99, IT."} et sqq.; bibliography, 129 Rhizoctonia, i.-s Rhizoctonia, 1 7, 18 Rhizomorph, 1 Rhizopus, 10 R. nigricans, \ 2. 27 et sqq., 32 Rhode iendron ferrugineuni , 2 1 R. hirsutum, 21 Rhynia, 1 Rk yparobius. 36 R. brunneus, 1 2 1 R. (Thecotheus) Pelletieri, 120 R. polysporus, 1 2 1 Rhytisma Aceiinum, 21, ;- (Fig. 21, 133 (Fig. ' 93) Robinson, W., 14, 20, 29, 31, 33, 199 Roestelia, 202 Rosellina quercina, 140, 158 Rouppert, C, 1 28, 1 2c; idaeus, 2 1 Rust-fungi, see UredinaU 5 INDEX Saccardo, P. A., 222 Saccharomyces, 62, 63 (Fig. 24) S. pyreformis, 1 r Saccharomycetaceae, 7, II, 52, 55, 56, 57. 62 et sqq.\ bibliography, 65 Saccharomycodes Ludwigii, 6$ Saccharomycopsis capsularis, 63 (Fig. 24) Saccobolus ■violascens, 120 (Fig. 82) Sachs, J. von, 32, 33, 49 Sake, 12 Salicaceae, 18 Salmon, E. S., 23, 25, 26. 79, 89, 90; see also Massee and Salmon Sanisu, 74 Sands, M. C, 88, 89 Sappin-Trouffy, P., 204, 205, 212, 220 Saprolegniales. .= Saprophytes, 6 Saprophytism, 6, 7 et sqq.\ bibliography. 1:: specialization of, 20 et si/(/. Sareodes sanguined, 19 Scales, F. M., 13; see also McBeth and Scales Schikorra, W. , 46, 74, 75, 76 Schionning, H., 63, 65 ; see also Klocker and Schionning Schizanthtis Grakami, 21 Schizosccbaromyces mellacei, 63 (Fig. 24), 64 .S. oclosfiorus, 63 (Fig. 24), 64 (Fig. 25) X Pom be, 64 Schmitz, F., 41 Schoeler, N. P., 210 Schrenk, H. von, 12 Schroter, J., 222 Schwanniomyces occidentalism 64 Sclerotinia, 123 S. bulborum, 123 6". einerea, 123 S.fructigena, 123 S. Led:, 2; S. sclerotiorum, 123 S. tuberosa, 21, 123, 124 (Fig. 86) 5. Vaccmii, 1 24 Sclerotium, 1, 124, 150, 152 Scolecite. 39, 50, 99, ii'i Seaver, F. J., 146 Selaginella, 18 Sepultaria, 97 S. coronaria, 37 (Fig. j), 97 (Fig. =,=,) Sexual reproduction, 2, 103; andsce conjugation, fertilization, pseudapogamy Sharp, L. W. , 221 Sheath, 69, 85, 14S Smuts, see Ustilaginales Soil, fungi on, 7 Solanaceae, 18, 21 Solanum, 18 Solms Laubach, H. zu, 184, 195 Soot fungi. 12 Sooty-mould, 90 Sordaria, 9, 10, 30, 38 (Fig. 6), 139 (Fig. 100) S. Brefeldii, 158 -5". copropkila, 158 S.fimicola, 140 (Fig. 101) S. Jimiseda, 140, 157 S. globosa, 1 5S S. macrospora, 21, 140. 157 (Fig. 116) Sordariaceae, 8, 1 54, 156; et sac/, bibliography, ijS Sore-skin fungus, 28 Sorosporium, 187 Sorus, 184, 196 Spathularia clavata, 131 (Figs. 91,92) Specialization, 20 et sqq., 211 Spermatial hypha, 146, 163. 199, 207 Spermatium, 39, 146, 164, 173, 174, 199 Spermogonium, 147 (Fig. 106), 163, 198 Sphaeelotheca, 187 Sphaeria, 127 Sphaeriaceae, 154. 158 Sphaeriales, 6, 140, 142, 153 et seq. Sphaerosotua, 128, 1:9 S. fuscescens, 129 (Fig. 89) S.Janczeiuskianum, 128 (Fig. 88), 129 Sphaerotheea, 52, 53, 83 S. Castagnei (see .S. Humuli) S. Humuli, 41, 42 (Fig. 9), 84 (Fig. 41), 85 (Fig. 42) .S". mors-uvae, 8r, 82, 86 S. pannosa, 80 (Fig. 38) Spore, I. 3. 4, 35, 48, 161, 172, 196 Spore-ball, 184, 187, 194 Spore-formation, 48, 49 Spore forms, omission of, in Uredinales, 207 Spore mother-cell, 3, 35 Sporidium, 198 Sporormia intermedia, 157 (Fig. 117) Sprouting, 5 Stakman, E. C, Piemeisel, F. J., and Levine, M. X., 26, 27 Staling substances, 27 Stalk, of antheridial branch, 39, 87, 88; of archicarp, 85, 87, 88 Sterigma, 183 Sterile cell (Uredinales), 200, 207 Stevens, F. L., 39, 222 and Hall.'j. G., 28, 32, 3:, Stictaceae, 132 SHgeosporium, 19 Stigmatomyces Baeii, 174, 175 (Fig. 136), 176, '77 (Fig- 139) S. Sarcophagae, 177, 178 (Fig. 141) Stimuli, reactions to, 27 et sqq.; bibliography, 33 Stoppel, R., 58, 6 1 Strasburger, E., 31, 33 Strawberry mildew, 84 Streeter, S. G., 31, 32, 33 Strickena, 1, 142 (Fig. 104), 159 (Fig. 119) Stroma, I, 32, 140. 14 = , 149, 150, 166, 168 Sub-hymenial layer, 3, 95 Substrata, fatty, 10 Swanton, E. YV., 222 Symbionts, 6 Symbiosis, 6, 16 el sqq.; bibliography, 19 Sync/iytrium, 16 S. aureum, 2 1 Synkaryon, 201 Tapesia fusca, 123 Taphrina, 15, 93 T. aurea, 92 (Fig. 49), 93 (Fig. 50) T. Cerasi, 94 T. Kusanoi, 94 Tavel, F. von, 40, 222 Teleutosorus, 205, 206 INDEX Teleutospore, :;,, 196, 197. 2°5. ^r'. -<-• "81 219, 220 Teleutospore cell, 183, i << 7 . :o; fa olbiensis, 77 1 Fig. 36), 7S (Fig. 37) Terfeziaceae, 8, =7. 77 Thaxter, K., 171, 17:. 17.;. 174. '75i '76, '77. 17S, [79, 1S0, [8l, iS; Thelebolus, 50 /'. stereoreus, 120 (Fig. 83), 121 (Kigs. 84, 85) 7'. Zukalii, 1 2: Thermutis orlutin \ 1 fi Thiela 1, 68 Thiessen, F . 91 Thom. Cm 76 Tieghem, Ph. van, 40. 102. 107 TUMia, 1S7, ig3 7". / ' . [93 T laevts, 194 7". Trilici, 185 (Fig. 148), [87, 193 (Fig. .6.) Tilletiaceae, 193: bibliography, 195 Torn! : ', 64 Tragopogon pt Uensis, 189 Tranzschel, \\\, 211, 220 Tremellales, fi, 183 Tremellodon, 33 Trichogyne, 39. 5'. 52. 53< 54. 7'. 74. 98- 99' 103. 171 . 1 76. 21; 0/r/a terreum, ry Trichophoric cell, (No 1 agmidium, 2 19 7'. Ulmariae, iy6 (Fig. 164), 212, 216 (Fig. 196) Truffles, 8, 138 Tuber, 8, 35, 137 T. puberulum, [37, 138 (Fig. 99) r. ra/««, 136 (Fig. 97), 137 (Fig. 98) Tuberaceae, ly, y7, 135 et seq., 144; biblio- graphy. 138 Tuberales, 6, s. 97, 100, 135 Tubeuf, K. F. von. 18, 222 Tuburcinia, 186, 187 T. primulicola, 188, 11)4, [95 Tulasne, 1.. R. and C, 77, 78, 102, 107. 136,137, 150, ififi. 167, [68, 170, 1S7, [95, iyfi, iy7, Umbelliferae, 18 C>!. inula, 82 U- A* 'ris, 83 (Fig. 40) V. necator, 81, 83 Uniseriate spores, 36. 37 (Fig. 5) Uredineae, tee I 'redinali s Uredinales, 2. fi, 15, 22, 181, [83, 196 et sqq. bibliography, 220 . Z04, 2 \>> Uredosorus, 204, :ofi. 207, 2ifi Uredospore, 23, 204 Urocystis, 187 U. Anemones, iy+ (Fig. 163) U. Fischeri, 1 S7 1 Fig. 1 = 11 U. Violae, 184 : ,■:;, 199, 205. 2 iS. 219 U. appeiulnulatus , 196 (Fig. 164) U. Cunninghamianus, 2 1 7 U. Faba . 199 U. Fit at hi, . 20N Uromyces (cut.) U. Poac, 200 (Figs. 170. 171), 203 (Fig. i7fi), 212 (Fig. 188), 214 (Fig. 193) U. Stilltirum, 207, 21 1 U. Scirpi, 2 1 2 1 parvifolia, iyfi Qstilaginaceae, 188./ sqq. Ustilaginales, 5, 6, 15, ifi, 183. 184 ?t s,/,/. Ustilago, i=. [87, 188 r. ant/ierarum, 184. isfi (Fig. 149). 191 (Fig. 15S1. [92 (Fig. [59) / '. Avenae, 189 U. Carba, 187 (Fig. 1 = 2), 188, iSy (Fig. ■S3) U. Hordei, [86 (Fig. 150), 189 (Fig. 154) U. levis, r 9 2 (Fig. 160) /'. Uaydis, 21, 184, 190 (Fig. isfi), iyi (I ig. '57). "95 U. Scabiosae, 1S5 (Fig. 147) U. Tragoponis prattnsis, iSy, [90 (Fig. [55) U. Treubii, 184 (Fig. 146) r. 7W//,/. 189 6r. Vaillantii, iyi, 195 £/. violacea, 21, 184 £/. Zt-af, 193 Vaccinieae, 124 Vallory, J., 155, [56 KaAvz, 165 Valsaceae, 154. 164 Vattda, 17 Varilov, I., 27 Venturia, 161 Verpa, 1 29 Verrucose spore, 5 / 'iiia faba, 1 3 Wager, II.. 31, 33, (^ and Peniston, A., 66 Walled non-motile spore, 4 Ward, 11. Marshall, 11, 12, 19, 23, 2;. 26, 27, 76, 77, iyj, 21 1, 220 Weiss, F. E , 20 \\ el ford, E. J., 9, 1 2. 47, 48, 117. 122. 14.:, 203, 214, 216, 22 j and Blackmail, V. II., see Blackman and Welsford and Fraser, II. C. I., see Fraser and Welsford Werth, E., and Ludwig, K., [92, [95, 20s. 2:1 West. Cm -° Wheat mildew, 23. 7y, 210 /; : lia Saturnu . 6 Wilson, M.. [94, iy,s u inge, O., 85, 86, 89 Winter, ( ... 50, 222 Witi h's-broom, [6, yo. y 1 Wolf, F. A., 158 Wolfe, J. Jm 173 Wolk, |. P. van id 1. 6l, 6l Wolkia decolorans, 60, 6r W01 1. 7 Wormald, II, 22,27 Woronin, M.. 157. 1 58, [63 Wi ironin'n hypha, 142 Horoiiina, 1 = \\ mnd parasites, 14 232 INDEX Xytaria ffyfioxylon, 167 (Fig. 124) Zodiomyces, 27 X. polyworpha, 141 (Fig. 103), 170 (Figs. 11H, Z. vorticellarins, 173 (Fig. 133), 176 (Fig. [38) I2q) Zoosporangium, 4, 15 X. Tulasnei, 21 Zoospore, 1, 4, 15 Xylariaceae, 154, 165 ct sqq. ; bibliography, 170 Zopf, W., 156, I ,s8 Zukal, H., 73, 76 it ,• o Zygomycetes, 5, 8 Yamanouchi, S., 173 Zyiosaicharomyces, 63 (Fig. 24) Yeasts, 2, 7, 11 ; and see Saccharomycetaceae g Barkeri 64 Z. Chevalieri, 64 Zaghouania, 220 Zygotaxis .27 Zea Mays, 21, 190 Zymase, 10, 12, 62 PRINTED IN ENGLAND BY J. B. PEACE, M.A. AT THE CAMBRIDGE UNIVERSITY PRESS Nvw Yor;;;?.:.;:;.*:f.".- .:L':.:.r:-.:{'--:T^".:|ir . , ,. ,:. ...... r. .... ■:■ ".■ -.-■■ ''."■ . -. :-: ■;-' : ■ ; . ■■;....-....■.. .