Pythium, Peronospore, Completoria, Vol utelta, Botrytis, &c. That such overturgescence should lead to the bursting of fleshy fruits, such as gooseberries, tomatoes and grapes, is not surprising, nor can we wonder that fermentation and mould Fungi rapidly spread in such fruits; and the same is true for bulbs and herbaceous organs generally.
Stem rot, due to a mould (Botrytis sp.), occurs in wet weather.
The most destructive is Botrytis cinerea which forms orangebrown or buff specks on the stems, pedicels, leaves and flower-buds, which increase in size and become covered with a delicate grey mould, completely destroying or disfiguring the parts attacked.
Among the most fatal and disastrous of these diseases with which the cultivator had long to grapple was " muscardine," a malady due to the development of a fungus, Botrytis bassiana, in the body of the caterpillar.
In Botrytis the appressoria assume the form of dense tassels of short branches.
Among the enzymes already extracted from fungi are invertases (yeasts, moulds, &c.), which split cane-sugar and other complex sugars with hydrolysis into simpler sugars such as dextrose and levulose; diastases, which convert starches into sugars (Aspergillus, &c.); cytases, which dissolve cellulose similarly (Botrytis, &c.); peptases, using the term as a general one for all enzymes which convert proteids into peptones and other bodies (Penicillium, &c.); lipases, which break up fatty oils (Empusa, Phycomyces, &c.); oxydases, which bring about the oxidations and changes of colour observed in Boletus, and zymase, extracted by Buchner from yeast, which brings about the conversion of sugar into alcohol and carbondioxide.
Or the primary hypha y first swell at its apex, and put forth a series of short peg-like branches (sterigmata) from the increased surface thus provided, each of which develops a similar basipetal chain of conidia (Aspergillus), and various combinations of these processes result in the development of numerous varieties of exquisitely branched sporophores of this type (Botrytis, Botryosporium, Verticillium, &c.).
Some parasites attack many hosts and almost any tissue or organ (Botrytis cinerea), others are restricted to one family (Cystopus candidus) or genus (Phytophthora infestans) or even species (Pucciniastrum Padi), and it is customary to speak of rootparasites, leaf-parasites, &c., in expression of the fact that a given parasite occurs only on such organs - e.g.
Marshall Ward showed that the hyphae of Botrytis pierce the cell-walls of a lily by secreting a cytase and dissolving a hole through the membrane.
Miyoshi then demonstrated that if Botrytis is sown in a lamella of gelatine, and this lamella is superposed on another similar one to which a chemotropic substance is added, the tips of the hyphae at once turn from the former and enter the latter.
The sun is sufficiently powerful to cause the evaporation of the water in the grape through the skin without any preliminary loosening of the latter by the action of the botrytis cinerea or any other micro-organism.