THE FUNGUS BODY OF HYP HAL ELEMENTS. 43 



51. Parasites. Especially is this true of those fungi which 

 grow in the interior of living organisms. The higher plants 

 are liable to be fastened upon by parasitic fungi, and com- 

 pelled to act as hosts to their unbidden and unwelcome guests. 

 Such a host plant may be entered when a mere seedling, in 

 which case the fungus grows with its growth, or it may not 

 be attacked until older or even mature. The host may be 

 permeated in all its parts by the fungus filaments ; or certain 

 members, only, such as the leaves, flower parts or twigs, 



sp 



FIG. 51. Young hyphae of Exobasidiuin developing from spores, sp^ entering the 

 air-pores of the leaf of the cranberry. Others, from sp' , sp" , penetrate the skin 

 directly. Magnified about 600 aiam. After Woronin. 



may be affected. The effect of the fungus upon the host is 

 often scarcely visible to the unaided eye ; sometimes a 

 local disturbance is manifested by swelling, unnatural color 

 or growth ;* sometimes the affected members become dis- 

 torted and useless or are even killed ; sometimes the disease 

 is general and is followed, slowly or quickly, by general 

 death of the host. 



52. Infection. These internal parasites obtain entrance 



* See further ^ 222, 464. 



