MORPHOLOGY OF THE MOLDS 51 



sporulation. The hyphae are more or less branched, con- 

 tinuous tubes. Such a mycelium is said to be nonseptate. 

 In general those molds which show a separate mycelium 

 have a single nucleus with the cytoplasm in each section 

 of the hyphae. In those molds which are nonseptate 

 numerous nuclei are to be found scattered throughout the 

 protoplasm. A cell is sometimes defined as a nucleus sur- 

 rounded by a bit of protoplasm, hence it is not incorrect 

 to speak of the nonseptate molds as being multicellular. 



a- 



FIG. 33. TYPES OF HYPHAE ix MOLDS, a. Nonseptate hypha. Note 

 numerous nuclei and absence of cross walls or septa, b. Septate 

 hypha. Note single nucleus in each cell. 



Structure of the Mold Cell. The cell of the mold does 

 not differ in many respects from that of the yeast. The 

 cell wall consists in some instances of a substance closely 

 resembling cellulose, in others it may contain callose and 

 pectose. It is sometimes markedly thickened. This is par- 

 ticularly true of the outer walls of spores and of resting 

 cells. Such are sometimes cutinized. Such cells may occa- 

 sionally show ridges, thickenings, spines, knobs, or other 

 protuberances. 



The nuclei may ordinarily be readily differentiated from 

 the remainder of the cytoplasm. In the young cell the 

 cytoplasm is relatively dense. In the older cells it becomes 



