196 NATURE OF FUNGI 



a necessity for a plant body that is complex, because each part is 

 adapted to the performance of one or another of the many func- 

 tions that cooperate in the construction and distribution of the 

 organic substances. Consequently, the fungi do not exhibit many 

 of the characteristics of chlorophyll-bearing plants. Their cell 

 walls are thin and inclose a watery, colorless protoplasm in which 

 are usually dispersed many small nuclei (Fig. 129). Whatever 



FIG. 129. A few cells from a branching filament of green mould, Peni- 

 cillium, showing the granular character of the cytoplasm and the absence 

 of platids. The colorless areas in the cells, vacuoles, contain principally 

 water. 



form the plant body may assume, it will usually be found to con- 

 sist of filaments of delicate cells or tubular growths, called hypha_g_ 

 (sing, hypha). These fine filaments or tubes are the essential 

 portion of any fungus and as they spread over the substance upon 

 which they feed they form a branching and interwoven mass of 

 threads collectively known as the mycelium. This structure is 

 well illustrated in the hyphae that spread over bread and fruits, 

 forming a cobwebby mass or mycelium that is commonly known 

 as mould or mildew. Even in the larger fungi, as the mushroom, 

 it will be found that the entire body is composed of a mass of 

 these delicate hyphae which spring from a mycelium in the 

 ground. We will expect to find remarkable departures in the 

 fungi from previous types because of their peculiar manner of 

 obtaining food and also because they are largely terrestrial plants 

 and therefore exposed to a much wider series of conditions than 

 in the case of the algae. This will tend to cause variations and 

 so bring about new structures that are in harmony with the con- 

 ditions under which the plants live. As a rule, these variations 

 have been so extensive and have so completely changed the char- 



