LESSON XVIII 



PENICILLIUM AND AGARICUS 



ONE of the commonest and most familiar of the lower 

 organisms is the " green mould " which so quickly covers 

 with a thick sage-green growth any organic substances ex- 

 posed to damp, such as paste, jam, cheese, leather, &c. 

 This mould is a plant belonging, like Mucor, to the group 

 of Fungi, and is called Penicillium glaucum. 



Examined with the naked eye a growth of Penicillium is 

 seen to have a powdery appearance, and if the finger is 

 passed over it a quantity of extremely fine dust of a sage- 

 green colour comes away. This dust consists, as we shall 

 see, of the spores of Penicillium. The best way to study 

 the plant is to sow some of the spores in a saucer of 

 Pasteur's solution by 'drawing a needle or brush over a 

 growth of the mould and stirring it round in the fluid. 



It is as well to study the naked-eye appearances first. If 

 the quantity of spores taken is not too large and they are 

 sufficiently well diffused through the fluid, little or no trace 

 of them will be apparent to the naked eye. After a few 

 days, however, extremely small white dots appear on the 

 surface of the fluid ; these increase in size and are seen, 

 especially by the aid of a hand-magnifier, to consist of little 



