MetapJiyta Penicillium. 



93 



bread, be exposed to air and light for some days there will 

 usually be found over its surface at the end of that time a 

 dense white felt-work, which forms a tolerably firm cover- 

 ing to the underlying organic material. This is the so-called 

 * mycelium ' of Penicillium glaucum. We will assume that 

 the cultivation has been obtained pure, that is, free from 

 admixture with other moulds a result not always obtained. 

 Vegetative organs. The felt-like mass (fig. 26), when 

 examined under the microscope, is discovered to consist of 



FIG. 27. SPORE BEARING FILAMENTS OF Penicillium glaucum. 



fl /i 



1-6. Stages in the formation of the branched ends of the filaments. 



closely interwoven threads (hyphae) which branch and twist 

 in all directions. Each thread is composed of a variable 

 number of elongated cells placed end to end. Each cell con- 

 sists of a cellulose cell- wall, containing colourless granular 

 protoplasm. The threads branch and form a loose cellular 

 tissue, which may be termed a thallus, as being comparable 

 in all respects to the thallus of the Fucus. In Penicillium 

 the thallus is entirely composed of elongated cells loosely 



