Part 23

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.