Section I— Causation 

 CHAPTER I 



DISEASES CAUSED BY FUNGI 



The Nature of Fungi. 



Fungi are vegetable growths, that is, they are plants, but of 

 a relatively simple kind. They range in form from single 

 rounded cells or small cell-groups as in the yeasts, through 

 filamentous forms such as are familiar in the moulds common on 

 bread, cheese, or fruit, to elaborately shaped structures, with 

 tissues built up of filaments, more or less closely amalgamated, 

 of which mushrooms, toadstools, and the bracket-like outgrowths 

 which appear on dead trees are examples. 



The nearest relationship of fungi is with another large group 

 of simple plants, the Algse, which similarly range from single- 

 celled or filamentous forms such as produce the green colour or 

 the green slimy growth in any body of exposed water to the 

 large and variously fashioned forms known as seaweeds. 



There is an essential difference between Algae and Fungi 

 in the nature of the materials from which they derive their 

 nutrition. The Algse possess, in common with most forms of 

 vegetation, the green colouring matter chlorophyll, which 

 enables them to build up from inorganic materials — mineral 

 salts, carbon dioxide, and water — the organic compounds 

 required for construction and maintenance. Fungi, on the other 

 hand, have no chlorophyll and therefore no such ability, and can 

 live and grow only at the expense of material which has been 

 previously elaborated by some other plant or animal. It is the 

 mode of life arising from this necessity which gives to fungi their 

 great importance in human economy. 



Transitional forms are, however, known between Algae and 

 Fungi in respect of the chlorophyll content of the former, and 

 some Algas may assume a parasitic habit. 



There are fungi ready to take advantage of all classes of 

 vegetable or animal material if the conditions are favourable ; 

 they precede, accompany, or follow the even simpler organisms 

 known as bacteria, most of which are nourished in a similar way. 

 With them they are responsible for the degeneration of dead 

 vegetable or animal matter, which is called in general terms 

 decay, while the parasitic species have become adapted to feed 

 at the expense of living plants or animals. 



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