EDIBLE FUNGI— YEAST 255 



In many cases, unfortunately, no adequate remedy has yet been 

 discovered, and the only advisable procedure, in the event of 

 an outbreak of disease, is to burn all infected plants, so as to 

 prevent the spread of the parasite. 



Fungi are, however, not only of importance in causing decay 

 and disease, but also afford several greatly prized articles of 

 diet {e.g. Mushrooms, Truffles, Morels, etc.), although their actual 

 food-value is probably small. The great majority of the British 

 Basidiomycetes are innocuous, but there are a certain number 

 of species, some very widely distributed, which harbour deadly 

 poisons (alkaloids, etc.), and attention may be drawn to the fact 

 that such Fungi are by no means alwaj's highly coloured (Fig. 137) . 

 As examples of poisonous forms we may mention the Fly Toad- 

 stool {Amanita muscaria) and the Death Cap {Amanita 

 phalloides). The sclerotia of an Australian species of Polyporits, 

 which may attain the size of a football, are eaten by the natives. 

 An edible Fungus of another kind is seen in the so-called Vegetable 

 Caterpillar {Cordyceps), where a dense mass of hyphs or sclero- 

 tium completely replaces the internal organs of the animal ; this 

 parasite is extensivelj' cultivated in parts of the East and used 

 as a condiment. Fungi are not often employed in medicine, 

 except for the powdered sclerotium of the Ergot {Claviccps) 

 which contains a nitrogen base having the property of causing 

 muscular contraction. 



The production of most alcoholic beverages is due to the 

 activity of Yeasts {Saccharomyces), whose exact relationship to 

 other Fungi is not quite clear. The Yeast-plant (Fig. 140) con- 

 sists of oval cells, which are either isolated {a) or adhere together 

 in short chains (c), each the product of a peculiar method of 

 division of a single individual. The thin-walled cells contain a 

 large central vacuole (Fig. 140, e, va.), and, in contact with the 

 latter at one point, a nucleolus with surrounding chromatin (w.), 

 which become apparent on staining the living cells with a dilute 

 aqueous solution of methylene blue ; vacuole, nucleolus, etc., 

 together probably represent the nucleus. The Yeast-cells often 

 contain large glycogen- vacuoles {g.), as well as small bodies {v.), 

 stained deeply by methylene blue, and known as volutin-granules, 

 which appear to constitute another kind of reserve. 



When a cell has reached a certain size, it gives rise to a small 



