Part 12

Order 1. =Erysiphaceæ, Mildews.= The Fungi belonging to this order are epiphytic parasites, whose mycelium, somewhat resembling a cobweb, may be seen on the leaves and other green portions of plants (see Figs. 107, 108). The hyphæ ramify in all directions upon the surface of their host, and emit haustoria which penetrate the epidermal cells, and thus derive the necessary nutriment. The Mildew-Fungi thus belong to the obligate parasites, and during their growth dwarf and destroy the portions of their host on which they live. The reproduction takes place in the first instance by abstriction of conidio-chains from the end of special branches (Fig. 108 _c_, a hypha is seen in the act of detaching a conidium). The conidia may germinate immediately, and thus quickly reproduce their species. When present in large numbers they appear as a white meal covering the surface of the plant on which the fungus is found. Later on appear the dark brown, spheroid ascocarps (Fig. 108 _a_) which, although small, are generally just visible to the naked eye as black specks.

A characteristic feature of the Mildew-Fungi is the thin, pseudo-parenchymatous covering of the ascocarp, enclosing _one_ (_Podosphæra_ and _Sphærotheca_; compare _Thelebolus_ among the Hemiasci) or _a few_ asci (Fig. 108 _c_), which do not form any hymenium, but are irregularly placed. The cells of the ascocarp-envelope are often prolonged into hair-like appendages. The ascocarps are developed from the mycelium at places where two hyphæ cross each other (Fig. 107). At these places two short and erect hyphæ are produced side by side. The one from the lower hypha (Fig. 107 _c_) assumes an ellipsoidal shape, and is known as the _archicarp_ or _ascogone_, while the other (“_pollinodium_”) arches over the ascogone. From the latter one ascus may be at once developed (_Sphærotheca_, etc.), or after its division several asci may be produced, each developed from one division. The sterile hypha (termed “pollinodium,” since it was formerly, but erroneously, supposed to fertilise the ascogone) produces a number of branches, and forms the pseudo-parenchymatous envelope of one cell in thickness, enclosing the asci.

Many plants, both cultivated and wild, are attacked by various species of Mildew. A common means of prevention against their attacks is to dust the diseased parts with sulphur.

_Sphærotheca pannosa_ occurs on the leaves of Roses, and on the fruit of Peaches and Apricots. _S. castagnei_ on _Humulus_, _Cucumis_, etc.--_Erysiphe tuckeri_ grows on the leaves and fruit of the Vine; it spins its hyphæ over the bunches of grapes, curtails their growth, and causes them to burst, and to become decayed and rotten (Grape-disease). The Fungus was first noticed in England in 1845, and later was found in all countries where grapes are grown. It is only known in the conidial form (“Oidium tuckeri”). Many other species of _Erysiphe_ are found on herbaceous plants.--_Microsphæra_ has appendages which are repeatedly forked at their extremities. _M. grossulariæ_ on _Ribes grossularia_.--_Uncinula_ has appendages with spirally-coiled extremities; on _Salix_ and _Acer_.--_Phyllactinia_ has a circle of bristle-like appendages with dilated bases. _P. guttata_ on _Corylus_, _Fraxinus_, _Fagus_, etc.

Order 2. =Perisporiaceæ=, Moulds and Mildews. A group of Fungi widely distributed and found in all situations. Usually they have a well-developed surface mycelium, and small, round, seldom conspicuous ascocarps, containing ovoid, pulley-like spores. They are partly saprophytic, partly parasitic, in the latter condition having a brown mycelium.

_Eurotium glaucum_ (= _E. herbariorum_, Figs. 109, 110) and _E. repens_ live on dead organic matter, preserved fruits, etc. The conidial forms of both species are known as “Moulds” (Fig. 109), and formerly were described under the name “_Aspergillus glaucus_.” The conidia for some time remain attached to each other in chains (Fig. 109 _a_); they are abstricted from sterigmata arranged radially on the spherical, swollen end of the conidiophore. The small yellow or brownish ascocarps are frequently found in herbaria, especially when the specimens have been insufficiently dried. _Aspergillus fumigatus_ and others are pathogenic, causing mycosis in warm-blooded animals.

_Penicillium crustaceum_ (_P. glaucum_, Figs. 111, 112) is an exceedingly common “Mould.” Its mycelium appears very frequently on any organic matter which is permitted to remain untouched, and soon covers it with a dense mass of blue-green conidiophores. These branch at their summits and bear flask-shaped cells from which the conidia are abstricted. The ascocarps which, both in size and colour, resemble grains of sand, have only been obtained in luxuriant cultivation with a limited supply of oxygen.

_Capnodium salicinum_ (_Fumago salicina_, _Cladosporium fumago_), a common Mildew, forms dark overgrowths on the leaves and branches of various shrubs (Poplars, Elms, Willows) and on Hops. The conidia appear in various forms, as on conidiophores, in conidiocarps with large multicellular conidia, and in conidiocarps with small unicellular conidia; in nutritive solutions yeast-like conidia are also developed.--_Apiosporium pinophilum_ produces mildew on the leaves of _Abies alba_ and _Picea excelsa_. (The conidial-forms were formerly described as “_Antennaria pinophila_”).

Order 3. =Tuberaceæ, Truffles.= The Fungi belonging to this order are entirely subterranean. The mycelium is filamentous, and partly parasitic upon the roots of plants, especially trees, in its neighbourhood; it is then known as _Mycorhiza_. The fruit-body is relatively large, in some cases about the size of a hen’s egg. Internally it is traversed by a number of winding passages (Fig. 113 _a_), the walls of which are coated with the asci. The asci (_b_) contain only a small number of spores, and these are set free by the putrefaction of the fruit-body. Conidia are unknown.

_Tuber melanosporum_, _T. brumale_, _T. æstivum_, and other species are edible. _Terfezia leonis_ and _Choiromyces mæandriformis_ are also edible. The Truffles are always found in woods and under trees, and disappear when these are destroyed. France and Italy produce the best and the largest number of Truffles, which are hunted by specially trained dogs and pigs.

In _Elaphomyces_ (Stag-Truffle) the fruit-body has a corky external layer, and is inedible. Some of the species are found in this country. _E. granulatus_ is parasitic on the roots of the Fir.

Family 3. =Pyrenomycetes.=

In this family the hymenium is enclosed in small fruit-bodies, _perithecia_ (Fig. 120 _b_), which appear to the naked eye as small dots. In shape they resemble a globe or a flask with a narrow mouth, through which the spores are ejected (peronocarpic ascocarps). Different kinds of reproduction--conidia, pycnidia (chiefly with microconidia), chlamydospores, and perithecia--are found in the same species. The various stages in the life-history of these Fungi are so dissimilar, that formally they were considered to be different genera. Ergot furnishes a very good example.

This family may be subdivided into 3 sub-families.

Sub-Family 1. =Hypocreales.=

The perithecia are _pale, fleshy, brightly coloured_, and generally aggregated on a stroma. Conidia and chlamydospores occur very frequently. Only one order.

Order. =Hypocreaceæ.= In this order the majority are parasites upon Flowering-plants (_Nectria_, _Polystigma_, _Epichloë_, _Claviceps_); but some are parasites upon Fungi (_Hypomyces_, _Melanospora_), or upon insects (_Cordyceps_).

The most important member of this order is the ERGOT (_Claviceps purpurea_, Figs. 114, 115, 116). This Fungus is found in the flowers of many species of Grasses, especially the Rye, attacking and destroying the ovaries. In the FIRST or CONIDIAL STAGE of the attack, the ovaries are found covered with a white, irregularly folded mycelium (Fig. 114 _m_, Fig. 115), formed of numerous hyphæ woven together and penetrating the wall of the ovary. From these a number of hyphæ (Fig. 114 _a_) project into the air and abstrict from their apices the conidia (_b_) which serve as reproductive organs. The mycelium also secretes a sticky, stinking fluid (honey-dew) in which the conidia are embedded in great numbers. The honey-dew exudes from the bases of the glumes, and is greedily sought by flies, which thus carry the conidia to other ovaries. In this manner fresh ears are infected, which might escape were the conidia only distributed by the wind. This stage formerly was regarded as an independent Fungus, known as _Sphacelia segetum_ (Fig. 115). On germination, the conidia produce either a new mycelium (Fig. 114 _d_, _c_), or new conidia. The SECOND or SCLEROTIUM STAGE is the one in which the Fungus passes the winter. The mycelium penetrates deeper and deeper into the attacked ovaries, their tissues are destroyed and replaced by the hyphæ, which gradually become more and more felted together. A firm, pseudo-parenchymatous mass of hyphæ is thus formed at the base of the loosely-woven _Sphacelia_, which is in part transformed into the hard sclerotium, and the remainder thrown off. A dark, hard, poisonous body, longer than the natural grain, is thus formed; these bodies are known as Ergots, and were formerly considered to be a distinct species,--_Sclerotium clavus_ (“Secale cornutum,” Ergot, Fig. 116 _A_, _c_). The THIRD STAGE, described as _Claviceps purpurea_, is developed in the following spring from the germinating sclerotium, which produces dark-red stromata with short stalks. In the stroma numerous perithecia with asci and ascospores are produced. The latter may infect young flowers of the cereals, in which the disease is then developed as before.

Several species of the genus _Nectria_, with blood-red perithecia, are found as dangerous parasites, especially _N. ditissima_, which causes “Canker” in the Beech, Ash, and Apple, etc.; _N. cucurbitula_, which appears on Pine-trees, and _N. cinnabarina_ (Fig. 117), whose conidial form was formerly named _Tubercularia vulgaris_.--_Polystigma rubrum_ forms shining red spots on the green leaves of _Prunus_-species.--_Epichloë typhina_ is parasitic on the sheaths of Grasses, on which it first forms a white conidial-layer, later on a yellow layer of perithecia.--_Cordyceps_ (Chrysalis Fungus, Figs. 118, 119) lives in and destroys insects, and after compassing their death produces the club-formed, generally yellow, stromata, one part of which bears conidia (_Isaria_) and another perithecia. _C. militaris_ (Fig. 118) on the chrysalides and caterpillars of moths, is the most common.

The so-called _Botrytis bassiana_, which produces the disease known by the name of “Muscardine,” in silkworms, is probably a conidial form belonging to _Cordyceps_.

Sub-Family 2. =Sphæriales.=

To this sub-family belong the majority of the Pyrenomycetes. The perithecia are of a _firm consistence_ (tough, leathery, woody or carbonaceous), and of a _dark_ colour. Their _covering_ is _quite distinct from the stroma_ when this structure is present. The stromata are sometimes very large, and may be either cushion-like, crustaceous, upright and club-like, or branched bodies. In general, small, inconspicuous Fungi, living on dead vegetable matter, sometimes parasites. Free conidiophores and conidiocarps are known in many species, and in several, chlamydospore-like forms of reproduction. Orders 3–18 constitute the Sphæriaceæ of older systematists.

Order 1. =Sordariaceæ.=--Fungi living on dung with fragile perithecia, either aerial or buried in the substratum. The dark brown or black spores have either a mucilaginous envelope (_Sordaria_, etc.) or mucilaginous appendages (_Podospora_), by means of which their expulsion and distribution are promoted.

Order 2. =Chætomiaceæ.= Perithecia fragile, free, bearing on the summit a tuft of hairs. _Chætomium_, on decaying vegetable matter.

Orders 3–7. _Perithecia scattered or aggregated, situated from the commencement on the surface of the substratum. Stroma wanting._

Order 3. =Trichosphæriaceæ.= _Trichosphæria parasitica_ (Fig. 121), on _Abies alba_; _Herpotrichia nigra_ on _Picea excelsa_ and _Pinus montana_.

Order 4. =Melanommaceæ.= _Rosellinia quercina_ lives in the roots of 1–3-year-old Oaks, and destroys the plants.

Order 5. =Ceratostomaceæ.=

Order 6. =Amphisphæriaceæ.= _Strickeria obducens_ (Fig. 120) has brick-like spores, and lives aggregated on the hard branches of _Fraxinus_.

Order 7. =Lophiostomaceæ.=

Order 8. =Cucurbitariaceæ.= Perithecia tufted, _at first embedded, then breaking through_, often situated upon an indistinct _stroma_.

Orders 9–13. _The perithecia remain embedded, and are only liberated by the casting off of the covering layers of the substratum. Stroma wanting._

Order 9. =Sphærellaceæ.= The species of _Sphærella_ have colourless, bicellular spores. They live upon the leaves of many plants, and develope spherical perithecia upon the fallen leaves.

Order 10. =Pleosporaceæ.= The conidial-forms of _Pleospora herbarum_ and _P. vulgaris_ form a black covering on various plants, known as “smuts.”--_Venturia ditricha_ occurs on the underside of dry Birch leaves, and perhaps to this belongs the conidial-form, _Fusicladium pirinum_, which causes the “Rust spots” on Apples and Pears.

Order 11. =Massariaceæ.=

Order 12. =Clypeosphæriaceæ.=

Order 13. =Gnomoniaceæ.= Perithecia, with peak-like aperture. _Gnomonia erythrostoma_ in the leaves of _Prunus avium_, which turn brown and do not fall in autumn.

Orders 14–18. _Stroma generally well developed. The perithecia are embedded in the stroma, but when this is rudimentary, in the substratum._

Order 14. =Valsaceæ.= _Valsa._

Order 15. =Diatrypaceæ.= _Diatrype._

Order 16. =Melanconidaceæ.=

Order 17. =Melogrammataceæ.=

Order 18. =Xylariaceæ.= This order is the most highly developed of the Sphæriales. The _stroma_ arises on the _surface of the substratum_, which is generally dead or decorticated wood; it is well-developed, crustaceous, hemispherical or upright. In the younger conditions it is covered with a layer of conidia, and later on it bears the _perithecia_, arranged in a layer immediately _beneath its surface_. The ascospores are of a dark colour. Often also there are free conidiophores.

_Hypoxylon_ and _Ustulina_ have a cushion-like or crustaceous stroma.--_Xylaria_ has a club-shaped or branched stroma, often several centimetres high. _X. hypoxylon_ (Fig. 122) and _X. polymorpha_ occur on old tree stumps.--_Poronia_ grows on old horse dung, and has a conical stroma.

Sub-Family 3. =Dothideales.=

The _perithecia_ are always embedded in a _black stroma_, and are _not distinctly separated_ from it. The accessory forms of reproduction are: conidiophores, conidiocarps, and yeast-like conidia. The majority are parasites. One order.

Order =Dothideaceæ=. _Phyllachora graminis_ produces scab-like patches on the leaves of the Grasses.--_Scirrhia rimosa_ grows on the leaf-sheathes of _Phragmites_.--_Rhopographus pteridis_ on _Pteridium aquilinum_.

Family 4. =Hysteriales.=

This family, like the following, has hemiangiocarpic ascocarps (_apothecia_). These are closed in the early stages, but when ripe _open_ in a _valvular manner_ by a _longitudinal fissure_; they are black, oblong, and often twisted. Some species are parasites, especially upon the Coniferæ.

Order 1. =Hysteriaceæ.= _Hysterium pulicare_ upon the ruptured bark of many trees.

Order 2. =Hypodermaceæ.= The species of _Lophodermium_ live upon the leaves of Conifers, and are the cause of their falling off (_blight_). _L. pinastri_ (Fig. 125), on the leaves of _Pinus_ and _Picea_; the leaves become red-brown and fall off; at first conidiocarps are formed, and later apothecia; _L. nervisequium_ (Fig. 123), on _Abies alba_; _L. macrosporum_ (Fig. 124), on _Picea excelsa_; _L. brachysporum_, on _Pinus strobus_.

Order 3. =Dichænaceæ.=

Order 4. =Acrospermaceæ.=

Family 5. =Discomycetes.=

The ascocarps (_apothecia_) are at first closed, and _only open_ at the time of their ripening, not valvularly, but more or less like a _saucer_ or _cup_, so that the hymenium lies exposed on their upper surface. In the first three sub-families, and generally also in the fourth, the apothecia are formed inside the substratum. The apothecia are, in contrast to the Pyrenomycetes, light and brightly coloured, and their size varies very much, and may be several centimetres in diameter. Paraphyses are often present between the asci; they often contain colouring matter, and give to the disc its characteristic colour. The tissue on which the asci are borne is known as the _hypothecium_. The shape and colour of the spores is not so varied as in the Pyrenomycetes. The accessory forms of reproduction are conidia (sometimes of two forms), chlamydospores, and oidia. The family is divided into 5 sub-families.

Sub-Family 1. =Phacidiales.=

The apothecia are developed in the interior of the substratum, which they break through, and in general dehisce apically. The envelope is tough and black. Hypothecium inconspicuous; hymenium flat.

Order 1. =Euphacidiaceæ.= _Phacidium abietinum_, on the leaves of _Abies alba_.--_Rhytisma_; the pycnidia are found in the summer on the green leaves, while the apothecia are developed on the fallen leaves and dehisce in the following spring. _R. acerinum_ causes black spots on the leaves of the Sycamore, and _R. salicinum_ on Willows.

Order 2. =Pseudophacidiaceæ.=

Sub-Family 2. =Stictidales.=

The apothecia when ripe break through the substratum which forms a border round them. Hymenium generally saucer-shaped.

Order 1. =Stictidaceæ.= _Stictis._

Order 2. =Ostropaceæ.= _Ostropa._

Sub-Family 3. =Tryblidiales.=

The apothecia are embedded in the substratum in the early stages, and then are raised high above it. Hypothecium thick. Hymenium cup-shaped.

Order 1. =Tryblidiaceæ.= _Tryblidium._

Order 2. =Heterosphæriaceæ.= _Heterosphæria patella_ on the dead stalks of Umbellifers.

Sub-Family 4. =Dermateales.=

The apothecia in the early stages are embedded in the substratum and then break through it, or are from the first situated on the surface of the substratum. Hypothecium thick.

Order 1. =Cenangiaceæ.= _Cenangium._

Order 2. =Dermateaceæ.= _Dermatea._

Order 3. =Patellariaceæ.= _Patellea_, _Biatorella_, _Patellaria_.

Order 4. =Caliciaceæ.= _Calicium_, _Coniocybe_, etc., on the bark of trees.

Order 5. =Arthoniaceæ.= _Arthonia_ on the bark of several trees. _Celidium stictarum_ on the apothecia of _Sticta pulmonaria_.