MICROBES, MOULDS, AND YEAST. 



21 I 



acid Q3.S, and water. The threads or Jiyphae secrete a 

 ferment, which decomposes the sugar. Those moulds 

 which grow upon plant tissues, such as dead leaves and 

 stems, are able to break up even the cell-walls, or 

 cellulose. They give out a special ferment, or cellulose 



Fig. 26. — CoNiDiA of Fungi, (i) Oidium lactis. (2) Peronospora Candida. 

 (3) Dematium pullulans. (4) Agaricus. (5) Uredospores of Puccinia. (6) 

 Penicillium glauciim. 



enzyme^ by means of which the fungus thread etches or 

 bores its way through the cell-wall. Thus vegetable 

 matter is first broken up by moulds, and then it is still 

 further destroyed by bacteria. Part of it goes back to 

 the air as carbonic acid, and part remains in the soil to 

 be used as food by other plants. The mould itself 

 decays rapidly as soon as it has exhausted its supply 

 of food material. Most moulds live on decaying 

 matters of one kind or another, such as horsedung, 

 dead leaves, decaying fruits, jams, bread, meats, etc. ; 



