CELLS OF FUNGI 3 



septa. Slow motion pictures of growing septate mycelia, however, 

 show that the streaming is very much cut down as soon as the septa 



are formed. 



Tlius the three main classes of fungi may be recognized, in part 

 at least, by the character of their mycelium: the Phycomycetes 

 possess non-septate or coenocytic mycelium (Fig. 1) ; the Ascomy- 

 cetes and Basidiomycetes septate mycelium. These characters, how- 

 ever, are not the main ones upon which the classification of fungi is 

 based, and are not absolutely constant, for the mycelium of both 

 Ascomycetes and Basidiomycetes may be non-septate when the plant 

 is very young, and the mycelium of Phycomycetes will develop septa 

 in certain conditions, as for separating off spores. 



Cells of Fungi. The cells of fungi are much like those of higher 

 organisms in their general characters. They possess a cell wall which 

 is frequently of appreciable thickness. This was formerly thought 

 to be composed of a substance similar to cellulose, though it does not 

 give the microchemical reactions of cellulose, and was called "fungus- 

 cellulose"; but more recent investigations indicate that it is chitin, 

 or a mixture or compound of chitin and cellulose. 



Within the cell wall is the cell proper, or protoplast. It contains 

 one or more nuclei, as indicated above. These are very small and 

 not easily demonstrated, special complicated staining methods being 

 required. The cytoplasm generally presents a granular or foamy 

 appearance due to the accumulation within it of various reserve sub- 

 stances in the form of granules or vacuoles. These may be of various 

 kinds— fat, carbohydrate, and protein. The amount of this reserve 

 material varies with the age of the mycelium ; in old portions of the 

 thallus it may nearly fill the cell. Fat appears in the form of very 

 highly rfefractile globules; it may be identified by staining with 

 Sudan III. Carbohydrate is stored as glycogen as in animals, not as 

 starch as in green plants. Protein is apparently stored in several 

 forms. A noteworthy reserve substance almost peculiar to fungi is 

 known as volutin or metachromatic material. It is identical with 

 the material found in some bacteria designated in them, metachro- 

 matic granules or polar bodies. It may appear either as granules or 

 as vacuoles, the former sometimes floating in the latter. It is prob- 

 ably a colloid which may exist in either the sol or the gel state. 

 There has been considerable discussion regarding its true nature 

 and function, which will be gone into in further detail in connection 

 with the yeasts. It is generally considered a reserve material and 

 recent studies indicate that it is a free mucleic acid differing slightly 



