Part 11

Order 3. =Saprolegniaceæ=, _Water-Fungi_ which live as saprophytes on organic remains lying in water, for instance, on dead flies (Fig. 93), worms, remains of plants; but they may also make their appearance on living animals, being frequently found, for example, on the young trout in rearing establishments.

The thallus is a single, long and branched cell. It has one portion which serves as root, and lives in the substratum, where it ramifies abundantly for the purpose of absorbing nourishment; and another portion projecting freely in the water, and sending out hyphæ on all sides (Fig. 93). The asexual reproduction takes place by swarmspores (Fig. 94), which are developed in large sporangia; these swarmspores generally possess two cilia, and on germination grow into new plants. The entire protoplasm in the oogonium is formed into one or more oospheres, without any surrounding “periplasm.” The oospheres may not be fertilised (p. 100), and then develope parthenogenetically.

Genera: _Saprolegnia_, whose swarmspores disperse immediately after having left the sporangium. _S. ferax_ is the cause of a disease in fish (“Salmon disease”) and in the crayfish.--_Achlya_, whose swarmspores accumulate in a hollow ball before the mouth of the sporangium.--_Leptomitus_ has strongly indented hyphæ, causing a “linked” appearance. _L. lacteus_ is frequent in the waste matter from sugar factories.--_Monoblepharis_ deviates from the others by the greater development of its fertilising process; the oosphere, situated in an open oogonium, becoming fertilised by self-motile spermatozoids, which are provided with a cilium at the posterior end.

Class 2. =Mesomycetes.=

The Mesomycetes are intermediate forms between the Phycomycetes and the Higher Fungi. In the vegetative organs, and in the multicellular hyphæ, they resemble the Higher Fungi; the methods of reproduction, however, show the characters of the Phycomycetes, namely sporangia and conidiophores of varying size and with varying number of spores; definite and typically formed asci and basidia are not present. Sexual reproduction is wanting. The HEMIASCI are transitional between the Phycomycetes and the Ascomycetes, the HEMIBASIDII (Brand-Fungi) form the transition to the Basidiomycetes.

Sub-Class 1. =Hemiasci.=

The Hemiasci are Fungi with _sporangia_ which, _although resembling asci_, yet have _not_, however, _a definite form and a definite number of spores_. Besides endospores, conidia, chlamydospores and oidia are found.

Order 1. =Ascoideaceæ.= _Ascoidea rubescens_ forms irregular, reddish-brown masses in the sap issuing from felled Beeches. It has _free sporangia_, which resemble asci in their structure, in the development and ejection, and in the definite shape and size of the spores. The formation of the sporangia takes place when the nutriment is nearly exhausted, and resembles that of the conidia, since they are developed from the end of a hypha which enlarges, and the swelling becomes separated by a transverse wall. Within the sporangia numerous spores of a cap-like form are developed, which are set free through an opening at the apex. Sporangia are formed successively at the apex of the same hypha, the second commencing to develope as the first is dehiscing. Conidia and sporangia are not formed simultaneously; the former may be considered as closed sporangia.

Order 2. =Protomycetaceæ.= _Protomyces pachydermus_ causes hard swellings on the stems and leaf-stalks of the Cichorieæ (_Taraxacum_, etc.). These swellings consist of _chlamydospores_ (resting-spores), which germinate and become free, ascus-like sporangia, with numerous small spores. In nutritive solutions the chlamydospores form conidia with yeast-like buddings. _P. macrosporus_ on _Ægopodium_, and other Umbelliferæ.

Order 3. =Thelebolaceæ.= _Thelebolus stercoreus_, is found on the dung of deer, hares, and rabbits, and has _closed sporangia_, which resemble asci in their shape and regular construction, and in the ejection of spores. The covering encloses only one sporangium, even where the sporangia arise close together.

This order, by reason of the covering of the sporangia, forms the transition from the Hemiasci to the Carpoasci, while the two first supply an intermediate step to the Exoasci.

Sub-Class 2. =Hemibasidii, Brand-Fungi.=

The Brand-Fungi (also known as USTILAGINEÆ) are Fungi with _basidia-like conidiophores_, which, however, have not yet advanced to a definite form or number of conidia. They are true parasites, whose mycelium spreads itself in the intercellular spaces of Flowering plants. The mycelium is colourless, quickly perishable, has transverse walls at some distance from each other (Fig. 96), and sends out haustoria into the cells of the host-plant.

It most frequently happens that the germ-tube enters the host-plant at its most tender age, that is, during the germination of the seed; the mycelium then wanders about in the tissues of the shoot during its growth, until it reaches that part of the plant where the spores are to be formed. The spore-formation takes place in the same way in all those species whose brand-spores are developed in the floral parts of the host-plant. Many Brand-Fungi have, however, a more local occurrence, and the mycelium is restricted to a smaller area of the leaf or stem. Those organs of the host-plant in which the brand-spores are developed often become strongly hypertrophied. In perennial plants the mycelium winters very often in the rhizome.

The brand-spores are the winter resting-spores of the Brand-Fungi. They arise in the tissues of the host-plant, which is often destroyed, and become free through the rupture of the epidermis; they are thick-walled, generally brown or violet, and very often possess warts, spines, or reticulate markings. Fruit-bodies, that is enclosed organs of reproduction, are found in few genera (_Sphacelotheca_, _Graphiola_; _Doassansia_, Fig. 97). In _Tolyposporium_, _Tuburcinia_, _Thecaphora_ (Fig. 102), etc., the brand-spores are united into a _ball of spores_. On germination the brand-spores behave as _chlamydospores_, namely, as the fundament of conidiophores, by emitting a short germ-tube, _i.e._ a conidiophore (“promycelium”). The USTILAGINACEÆ (Fig. 99, 2) have a short _transversely divided_ conidiophore, with _laterally_ developed conidia (comp. the basidia of the Protobasidiomycetes). The conidiophores of the TILLETIACEÆ are undivided (unicellular promycelia), and bear the conidia terminally, and so resemble the basidia of the Autobasidiomycetes.

In _Tilletia_, _Entyloma_, _Neovossia_, _Tuburcinia_, the brand-spores germinate and form basidia-like conidiophores with spindle-shaped conidia; their mycelium, on the other hand, produces later only single, sickle-shaped conidia, so that two kinds of conidia are found, as in a few Basidiomycetes. In some species, _e.g. Ustilago hordei_, the brand-spores only germinate vegetatively and form a mycelium. In nutritive solutions (solutions of dung, etc.) where they live as _saprophytes_, the brand-spores of many species emit germ-tubes, and on these, _yeast-like conidia_ are produced by repeated budding, which grow into mycelia only when the nutritive solution is exhausted. These conidia have not the power of producing alcoholic fermentation. The very numerous conidia, which are found in the dung of herbivorous animals, are probably the yeast-conidia of Brand-Fungi. The brand-spores, which are eaten by animals with the grain and hay, pass into the dung and without doubt give rise to a very rich multiplication of yeast-conidia.

The conidia (also called “sporidia”) of many species unite generally into an H-form (Figs. 97, 4; 100 h; 101, 4). This union in pairs does not, however, take place with a view to germination, there is no fusion of nuclei, and therefore in this “fusion” there is no sexual act.

Order 1. =Ustilaginaceæ.= Conidiophores with transverse walls and lateral conidia.--_Ustilago_ (Fig. 99) generally developes its spores in the floral organs of its host-plant, the ovary or anthers, where they arise from hyphæ, and form a slimy mass which when mature becomes a black dust.

To this order belong _U. avenæ_, parasitic on Oats, _U. hordei_ and _U. nuda_ (_U. jenseni_), on Barley; these are the usual cause of “Smut” on cereals. _U. hypodytes_ on straw of _Elymus_ and _Agropyrum_. _U. filiformis_ in the leaves of _Glyceria_. _U. caricis_ transforms the fruits of various species of _Carex_ into black, dusty balls. _U. violacea_ developes its violet spore-powder in the anthers of the Caryophyllaceæ. _U. tragopogonis_, transforms entire inflorescences of _Tragopogon_ into a black-violet mass. Among the largest are _U. grandis_, which causes the large swollen nodes in the stem of _Phragmites_, and the Maize Blight, _U. maydis_, which produces outgrowths about the size of a hand on the spadix of the Maize.

Order 2. =Tilletiaceæ.= Conidiophores undivided, generally several conidia arise at their apices.--_Tilletia tritici_, the _Stinkbrand on Wheat_ (Fig. 100). The mycelium lives in Wheat-plants, producing its spores in the ovary after the whole interior of this body has been destroyed by the mycelium, with the exception of the external layer of the wall of the ovary, which remains essentially unaltered and encloses the closely packed, firm mass of spores (Fig. 100 _d_). The grains of Wheat thus attacked are shorter and thicker than the sound ones, and the ears show the presence of this Fungus by their erect position, and the wide separation of the chaff (Fig. 100 _a_). The unpleasant odour of the ovary prior to the ripening of the spores, has given the name “Stinkbrand,” and, in like manner, its hardness when it encloses the ripe spores, is the reason of its being also called “Stonebrand.” On account of this hardness, the diseased grains are readily harvested together with the healthy ones, which become infected by the spores at the threshing. _T. lævis_ (_T. fœtens_) also occurs on Wheat and has smooth brand-spores.

_Entyloma_ (Fig. 96), a genus with numerous species, which appear in spots on the leaves of the host-plant, and _Tuburcinia_ (Fig. 98), which makes its appearance on the Primulaceæ, produce white conidia-spots on the surface of the host-plant. The first-named has single spores, the latter has its spores closely massed together.--_Urocystis_ (Fig. 101) has its spores surrounded by a number of small and lighter coloured barren spores. _U. occulta_, Rye-stem Blight, forms its spores in long streaks in the stems and leaves of the Rye, and does considerable damage. _U. cepulæ_ on Onions. _U. violæ_ forms large dark-violet swellings in the leaf-stalk and stems of Violets.--_Thecaphora_ (Fig. 102) appears in seedlings of _Convolvulus_ and _Astragalus_.

As a means of protection against the Smut-Fungi which make their appearance on the different cereals, a submersion of the grains in a solution of blue vitriol (½%) for twelve hours, or better still, submerging for five minutes in water heated to 53–55° _C_ (Jensen’s method) is employed.

Class 3. =Mycomycetes, Higher Fungi.=

The MYCOMYCETES are not entirely aquatic in habit; they have hyphæ with _transverse walls_, but _no sexual reproductive organs_. The asexual reproduction takes place in very different ways; by endospores (in asci), conidia, basidiospores, chlamydospores, and oidia. Swarmspores are never found.

Two chief methods of reproduction may be distinguished, and hence the class may be divided into two large sub-classes:--the ASCOMYCETES (with asci), and the BASIDIOMYCETES (with basidia).

Sub-Class 1. =Ascomycetes.=

The main characteristic which distinguishes the Ascomycetes is the _ascus_; a name given to a sporangium of a definite shape and size, and containing a definite number of spores. The shape is generally club-like or spherical, the number of spores 8 (in some 2, 4, 16 or more), see Figs. 103, 105, 108, 110, 113, 116, 120, 121, 123, 129.

In the lowest forms, the EXOASCI, the ascus springs directly from the mycelium without the formation of a fruit-body (_i.e._ ascocarp). In the higher forms, which contain many species, the CARPOASCI, the asci are united and form ascocarps which may be more or less enclosed (angiocarpic, hemiangiocarpic, and probably gymnocarpic).

The hyphæ of the _Mycelium_ in some remain free, in others they are felted together and form thick strands or flat, cushion-like bodies (compare in particular the stromata of the Pyrenomycetes). Some species form _sclerotia_ (Figs. 116, 128).

Asexual reproduction by means of _conidia_ is known in many species as the principal means of reproduction, and the one which affords the most rapid means of distribution. The conidia may be produced on conidiophores (Fig. 109), in conidial-layers (Fig. 122), and often in conidiocarps (pycnidia, Figs. 120 _d_, _e_; 123 _a_; 124 _b._). These last occur partly as the so-called “spermogonia” (that is, pycnidia with microconidia). The conidiophores never approach the basidia.

In many species the ascospores germinate and form conidia immediately (_Nectria cinnabarina_, _Sclerotinia_, _Taphrina_, etc.), sometimes while they are still in the ascus and before their ejection (_Taphrina_, Fig. 105 _a_). In many instances the conidia by means of continued budding can, for a longer or shorter time, produce yeast-conidia, _e.g. Taphrina_. In many other cases the conidia arise from the germ-tubes of the ascospores, or at any part of the mycelium. The unripe asci of _Taphrina_, when placed in water, develop conidia at their apices. The _Sclerotinia_-species produce numerous conidia whose germination has never been observed. The formation of conidia and asci sometimes takes place on the same fruit-body. In _Heterosphæria patella_ the conidia and asci are developed successively in the same fruit-body; in the ascocarps of _Dermatea frangula_ and _Sclerotinia sclerotiorum_ the formation of conidia may take place. The ascocarps frequently arise from the conidial-layers (_Nectria cinnabarina_, etc.). This relationship of the two forms of reproduction to each other may be explained by considering that both have descended phylogenetically from sporangia.

Sometimes _chlamydospores_ and _oidia_ also appear in the Ascomycetes; on germination, however, they do not, as in _Protomyces_, form sporangia, and on this account cannot be distinctly distinguished from conidia.

The asci are morphologically the highest form of reproduction and are always found at the close of the development of these Fungi; the accessory forms of reproduction are first developed, but a well-defined alternation of generations does not occur.

In the Ascomycetes there are more than 11,000 described species, which can be classed as follows:--

Series 1. EXOASCI. Only one order. „ 2. CARPOASCI. Family 1. _Gymnoascales_, } „ 2. _Perisporiales_, } Angiocarpic Carpoasci. „ 3. _Pyrenomycetes_, } „ 4. _Hysteriales_, } Hemiangiocarpic Carpoasci. „ 5. _Discomycetes_,} „ 6. _Helvellales_, Gymnocarpic (?) Carpoasci. Additional _Ascolichenes_: Lichen-forming Ascomycetes.

Series 1. =Exoasci.=

Ascomycetes with FREE ASCI; sometimes also conidia, chlamydospores and oidia. One order.

Order. =Taphrinaceæ.= Of the genera belonging to this order, _Taphrina_, _Endomyces_, and _Ascocorticium_, the first is most important.

_Endomyces decipiens_ is a parasite in the fruit-body of _Armillaria mellea_; _E. magnusii_ lives in the gelatinous, fermenting exudations of Oak-trees; _Ascocorticium albidum_ is found under the bark of the Fir-tree. _Endomyces_ has chlamydospores and oidia.

The species of _Taphrina_ are parasites, whose free asci may be found in great numbers, generally closely pressed together, on the parts of plants which they have attacked. The asci are developed directly from the ascogenous cells of a fertile, generally sub-cuticular, hypha, which arises from the sterile mycelium. The latter arises from the germinating ascospore, and may hibernate in the tissues of its host, particularly in the winter buds, and then with the commencement of the next period of vegetation it continues its growth side by side with that of its host. The hyphæ ramify in the intercellular spaces or beneath the cuticle, but have no haustoria. The ascospores (Fig. 105 _A_) and unripe asci may produce conidia.

Very remarkable appearances, and swellings of the attacked tissues, are produced when the mycelium is perennial; for example, the “Witches’-brooms” and “Pockets.” The hard, hollow, stoneless plums, known as “Pocket” or “Bladder” Plums, are produced by considerable changes in the tissues of the fruit; these are caused particularly by _T. pruni_ on several species of _Prunus_. The “Witches’-brooms,” on the contrary, are deformations of entire twigs or branches, and often attain a very large size. They occur on _Alnus incana_, caused by _T. epiphylla_; on _Carpinus betulus_, by _T. carpini_; on Cherry-trees, by _T. cerasi_; on Plum-trees, by _T. insititiæ_; on Birches, by _T. turgida_ and _T. betulina_. _T. deformans_ attacks the leaves of the Peach, and causes them to curl.

When a perennial mycelium is wanting, the infection is confined as a rule to white or yellow spots on the leaves, _e.g._ the commonest, _T. sadebeckii_, on _Alnus glutinosa_, and _T. aurea_ on species of _Populus_. _T. alni incanæ_ (Fig. 106) causes considerable hypertrophies on the pistillate catkins of the Alder, which may be compared to the “pockets” of _Prunus_.

Series 2. =Carpoasci.=

The Carpoasci are Ascomycetes, whose asci are enclosed in fruit-bodies, _i.e. ascocarps_. The accessory means of reproduction are free conidiophores (Fig. 109), conidial-layers (Fig. 122), conidiocarps (Fig. 120 _D_, _E_, etc.), chlamydospores and oidia.

For the different methods of distributing the ascospores, see p. 92.

Of the six families of the Carpoasci, the first three--_Gymnoascales_, _Perisporiales_, and _Pyrenomycetes_--are ANGIOCARPIC (that is, the ascocarp remains closed throughout its existence, and does not dehisce when ripe); the fourth and fifth families (_Hysteriales_ and _Discomycetes_), on the other hand, are HEMIANGIOCARPIC (the ascocarp, here also called an _apothecium_, is closed in the early stages, but opens at the commencement of ripening and exposes a hymenium of crowded asci); the family of _Helvellales_ has probably GYMNOCARPIC (or hemiangiocarpic) fruit-bodies.

Family 1. =Gymnoascales.=

The ascocarps are surrounded by a _spongy and incomplete envelope_. One order, poor in species.

Order =Gymnoascaceæ=.--The ascocarps are borne sometimes solitarily, or sometimes coiled together. _Gymnoascus reessii_ forms small bodies about 1 mm. in diameter on old horse-dung, which at first are white and afterwards orange-red.--_Ctenomyces serratus_ lives on the old feathers in birds’ nests.

Family 2. =Perisporiales.=

The ascocarps are surrounded by a _complete envelope_ without any opening: the fruit-bodies are cleistocarpic; the spores are only liberated after the disintegration of the fruit-bodies. Paraphyses are wanting. The two first orders have in addition the means of reproduction by conidia.