V.] MOULDS. 37 



LABORATORY WORK. 



1. PENICILLITJM. 



Prepare some Pasteur's fluid, and leave it exposed to tlie 

 air in saucers in a warm place : if Penicillium spores are at 

 hand add a few to the fluid in each saucer : if spores cannot 

 be obtained, the fluid, if simply left to itself, will probably 

 be covered with Penicillium in ten days or a fortnight. 

 Sometimes, however, the fluid will overrun with Bacteria, to 

 the exclusion of everything else. And very frequently other 

 moulds, such as Aspergillus, or Mucor, may appear instead of 

 or along with Penicillium. 



1. NAKED-EYE CHARACTERS. Note the powdery-looking 

 upper surface, white in young specimens, pale greenish 

 in older, and later still becoming dark sage-green .- 

 the smooth pale under surface : the dense tough 

 character of the mycelium. 



2. HlSTOLOGICAL STRUCTURE. 



a. The mycelium. 



a. Tease a bit out in water, and examine first with 

 low, and then with a high power : it is chiefly 

 made up of interlaced threads or tubes the 



a. Hyphce. Note their diameter (measure) form 

 subdivisions (cells) dichotomous mode of 

 branching and structure : the external homo- 

 geneous sac ; the granular less transparent pro- 

 toplasm ; the small round vacuoles. Draw. 



