« AnteriorContinuar »
where it continued to grow. When the seeding was done in winter (and only when done during the latter season), the mycelium often developed sclerotium-like bodies (Fig. 109 6), which were then transformed into perithecia. Janczewski never found these bodies in nature on the leaves of any kind of corn. Placed on nutrient gelatine they were covered by mycelium threads extending radially and often in large quantity. After a few days this mycelium formed conidia. The transformation of sclerotia into perithecia takes place quickly. The ascospores germinate easily on nutrient gelatine, and, in a few days, develop mycelia with the conidial form Cladosporium herbarum ; at the same time certain peculiar organs (Fig. 109 10) appear, the function of which is not known, and which are often found in the immediate neighbourhood of the conidiophores.
Cladosporium herbarum is very common on both dead and living plants. In breweries this fungus appears sometimes in large quantity on the walls of cellars; it is also found on malt, hops, etc. Like some other mould fungi it can give a cork taste to wine (Wortmann). it is not defined yet in how far it is identical with Hormodendron cladosporioides (Fres.) Sacc., yet both fungi are extremely like one another and the latter is probably often called Cladosporium. Janczewski says that he never succeeded in transforming Cladosporium into Hormodendron ; but the mycelium developed on the above sclerotia sometimes exhibited a development of conidiophores similar to those of Hormodendron. Another similar fungus is Fumago, very thoroughly studied by Zopf, which is specially to be recommended to those who intend taking up this question.
Order 1V.-Discomycetes. The ascophores are open and have a very varied appearance ; they may be either cup, disc, mussel or hat shaped. The asci generally contain 8 spores, but some species have 16, 32, 64, 128 and sometimes more. In many, conidia fructification is found in addition, and in some, sclerotium formation,
1. Genus : Sclerotinia, Fuckel. The mycelium produces sclerotia from which stipitate ascophores grow under certain conditions. Conidia fructification takes place.
Sclerotinia Fuckeliana, de Bary (Figs. 110 and 111). This species is best known as the conidia fructification under the name Botrytis cinerea, Persoon (B. rulgaris, Fr.). This fructification is usually developed first on the mycelium. The conidiophores, 1 to 2 mm. long, are branched at the top like panicles; the ends of the branches have bulbous swellings which bear numerous fine sterigmata which again abstrict large conidia. When the latter are ripe, the side branches bearing them die, so that new branches can then take their place.
If the conidia are seeded out in an unfavourable substratum, e.g., in a thin layer of water, they germinate and form a very short germ tube; from the latter or from small flaskshaped carriers small conidia (spermatia) are again abstricted, which, however, cannot be made to germinate. On the other hand, if the large conidia are put into a good substratum, a typical mycelium is developed which then forms either the usual large conidiophores or, under certain conditions, black sclerotia, a few millimetres thick. If such a sclerotium is brought into a damp atmosphere immediately after it gets ripe, conidiophores again develop; but, if it is kept at rest for a year at least, the ascophore develops in the shape of long-stalked cup fruits (Fig. 110 p).
spores of these asci may, like the large conidia, give r mycelia with large conidiophores or small conidioes of which the conidia do not germinate.
Fig. 110.-Sclerotinia Fuckeliana, de Bary. a, Sclerotium from which the Botrytis
conidiophores have grown ; 6, Sclerotium with two cupfruits ; C', Conidiophore of the Botrytis form ; m, Mycelium. 202. C", End of a conidiophore with branches and sterigmata. 394, k, Germinating conidium. 394. , Section of sclerotium with ascophore, p, (not much enlarged); n, An ascus with eight spores. 3f4. (After de Bary.)
In Botrytis cinerea, P. Lindner frequently observed the phenomenon of inter-growth. According to his investiga
tions, an irregular distribution of the plasma takes place in the older mycelia, some of the cells storing up large quantities of the contents, while others are completely emptied. The phenomenon of inter-growth is connected with this solely by the fact that the only cells which germinate inside the old mycelium are almost always rich in protoplasm. Fig. 111 represents a special case of this kind of germination, in which small conidia or spermatia are formed inside the cell. At the same time spermatia have also grown out laterally on the mycelium thread.
Oxalic acid is secreted in large quantity by the mycelia and sclerotia. Kissling showed that it forms a poison which kills living protoplasm. According to J. Behrens
Fig. 111.---Sclerotinia Fuckeliana, de Bary. The Botrytis form. Phenomenon of
inter-growth. Abstriction of small conidia (spermatia) inside a cell. (After P. Lindner.)
this poison is not an enzyme. Botrytis turns starch into sugar, and contains emulsin (Gérard).
This species is very widespread in nature, and occurs on all putrefying plant matter. It occurs as a parasite on vines, both on the leaves and grapes.
Botrytis cinerea may sometimes play an important part in wine manufacture. According to Müller-Thurgau, under certain circumstances it induces the so-called “Edelfäule" in the grapes, which forms the basis for attaining the highest concentration of the grape juice, and especially for the appearance of peculiar bouquet substances, the so-called sherry bouquet, in wines ; this occurs when it attacks quite ripe grapes, consumes the acid and, by rotting the skin,
allows the water to evaporate, and thus increases in a very high degree the concentration and sugar content of the berry. Wines thus made from over-ripe (edelfaul) grapes ferment very slowly. The cause of this is the separation of the protoplasm poison mentioned above, which reacts injuriously on the yeast, as was shown by J. Behrens. This injurious action can be prevented to some extent by a more vigorous nourishment of the yeast.
Grape must, in which Botrytis cinerea has been cultivated, contains an oxydase which, according to some investigators, causes the disease of wine which is known as “maladie de la casse," and which consists in a precipitation of the colouring material. Culture solutions of Botrytis when mixed with equal quantities of sound wine cause the colouring matter to precipitate completely in about four hours. The disease may be prevented by heating up to 70° C., when the oxydase becomes inactive (Laborde).
The opinion obtained formerly that this fungus was responsible for the smoky flavour of wine, but this is not the case (Mach, MüllerThurgau).
B.—IMPERFECT FUNGI (FUNGI IMPERFECTI). A large number of the fungi which have been discovered one by one by mycologists cannot yet be classified in the system set up by them; these fungi are therefore grouped for the present under the above name. This applies also to the following organisms, which are of interest for the fermentation industry.
The Torula Species. Originally the name Torula was given to hyphomycetes which had necklace-like, single or branched chains, of which the round or oval members were separable from one another. Later, however, the name included a number of different fungus species. Thus Turpin in 1838 calls Saccharomyces cerevisie Torula cerevisiæ, while the name Torula was afterwards given by Cohn to the necklace-like chains formed by the bacterium genus Micrococcus. Torula was understood by Pasteur to include yeast fungi with a very weak alcohol formation ; he did not mention whether they formed spores or not. The species of this kind might, therefore, be true