88 



PHYSIO LOG y. 



only a short branch of the mycelium, nutritive substances are taken by the 

 fungus from the protoplasm or cell-sap of the carnation. From here it 

 passes to the threads of the mycelium. These in turn supply food material 

 for the development of the dark brown gonidia, which we see form the dark- 

 looking powder on the spots. Many other fungi form haustoria, which take 

 up nutrient matters in the way described for the carnation rust. In the case 



Fig. 78. 



Cell from carnation leaf, showing 

 haustorium of rust mycelium grasping 

 the nucleus of the host. A, haustori- 

 um ; n, nucleus of host. 



Fig. 79. 



Intercellular mycelium with haustoria entering 

 the cells. A , of Cystopus candidus (white rust) ; 

 B, of Peronospora calotheca. (De Bary.) 



of other parasitic fungi the threads of the mycelium themselves penetrate 

 the cells of the host, while in still others the mycelium courses only between 

 the cells of the host (fungus of peach leaf-curl for example) and derives food 

 materials from the protoplasm or cell-sap of the host by the process of 

 osmosis. 



187. Nutrition of the larger fungi. If we select some one 

 of the larger fungi, the majority of which belong to the mush- 

 room family and its relatives, which is growing on a decaying log 

 or in the soil, we shall see on tearing open the log, or on remov- 

 ing the bark or part of the soil, as the case may be, that the 

 stem of the plant, if it have one, is connected with whitish 

 strands. During the spring, summer, or autumn months, exam- 

 ples of the mushrooms connected with these strands may usually 

 be found readily in the fields or woods, but during the winter and 



