LECTURE XII. 



MUCOR may be found growing on various moist organic sub- 

 stances. A piece of bread kept moist under a bell-glass usually 

 shows specimens of this plant in one or two days if kept at an 

 ordinary room temperature. 



The growth which is first noticed resembles very fine threads or 

 filaments of cotton-wool lying along the surface of the moist bread 

 and often spanning the little depressions and irregularities of its 

 surface. If these are examined carefully by probing with a pin or 

 a needle they will be found to branch, and it will be discovered 

 that they are held down by some of the branches which penetrate 

 into the bread. By continued development and branching of the 

 filaments the growth assumes the appearance of a felt covering 

 the bread more or less closely. The filaments forming this felt 

 and the branches which penetrate into the bread are called the 

 mycelium. After a day or so the mycelium sends up vertical 

 branches varying from 2 mm. to 2 cm. in length. At first these 

 branches which are quite straight and cylindrical have a rounded 

 end and like the horizontal branches of the mycelium are pure 

 white. Shortly, however, small globules begin to develop at their 

 tips and these darken in colour until they are quite black. When 

 they have developed this black colour the slightest touch suffices 

 to make them burst and to discharge a whitish mass of mucilage. 

 In addition to these globules which range from translucent white 

 to black, very often limpid drops of fluid may be seen adhering to 

 the vertical branches. 



Microscopic examination of the mycelium and of its vertical 

 branches shows the following : the mycelium consists of a single 

 coenocyte, on rare occasions showing transverse, septa. The 

 appearance of the creeping branches and those which penetrate 

 the bread are quite similar, both being covered by a delicate cell- 

 wall within which is a film of protoplasm. They- are called 

 hyphae. A clear colourless vacuole occupies the axis of the 

 branch. There is no appearance of chloroplasts or of any other 

 coloured bodies in the protoplasm or elsewhere. If one of these 



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