158 SAPROPHYTIC FUNGI 



the living body of an organism. A fungus which is 

 strictly confined to parasitism is called an obligate 

 parasite, one which can live either saprophytically or 

 parasitically is a facultative parasite. 



Moulds. — This name is commonly given to saprophytic 

 fungi which grow on organic substances, provided they 

 contain enough water, such as bread, jam, cheese, 

 leather, tobacco, etc., on which they produce whitish, 

 yellowish, greenish or bluish mycelia. They flourish 

 particularly when the air is very damp and warm. 

 In damp tropical climates any such substance will 

 become covered with mould in a day, if it is exposed 

 to the air. 



Mucor. — One of the commonest genera of white 

 moulds is Mucor, which forms a white, fluffy feltwork, 

 rather like cotton wool in appearance, in and on the 

 surface of such substances as those mentioned. If a 

 piece of this feltwork is examined under the micro- 

 scope it is seen to consist of delicate branched threads, 

 forming the mycelium or body of the fungus. The 

 mycelium of Mucor is a branched non-cellular tube, 

 the wall enclosing the cytoplasm, which contains 

 numerous very minute nuclei, though these cannot be 

 seen except by special methods of staining. The 

 cytoplasm encloses many vacuoles, which are smaller 

 towards the growing tips of the hyphse. The actual 

 tip of each hypha is rounded and the protoplasm at 

 the apex is without vacuoles. As the hypha g.rows 

 in length the nuclei at the tip constantly divide. 



The mycehum branches profusely, many of the 

 branches penetrating the substratum on which the 

 mould is growing, and absorbing hquid food. In this 

 way it acts hke the root of a higher plant, except that 

 here the food is largely organic. The essential ele- 



