114 DISEASE IN PLANTS. 



Examples of local action are furnished by 

 Schinzia, which forms gall-like swellings on the 

 roots of rushes; Gynmospormigium, which induces 

 excrescences on the stems of junipers, and 

 numerous leaf-fungi {Puccinia, Aicidiuin, Scptoria, 

 etc.), which cause yellow, brown, or black spots on 

 leaves, as well as by Ustilago, which attacks the 

 anthers or the ovary of various plants, and so 

 forth. In such cases the injury done by a few 

 centres of infection is very slight, but prolonged 

 action may bring into play secondary effects such 

 as the gradual destruction of the cambium round 

 a branch, when, of course, the effect of ringing 

 results ; or if the fungus becomes epidemic and 

 myriads of leaf-spots are formed, the destruction 

 of foliar tissue, gradual taxing of the assimilatory 

 cells, etc., may end in rapid defoliation, and 

 renewed attacks soon exhaust the plants and lead 

 to sterility and death, as often occurs with 

 Uredineae e.g. the coffee leaf-disease. 



It is highly probable that such fungi are particu- 

 larly exacting owing to their exhausting demands 

 for compounds of potassium, phosphoric acid, and 

 other bodies. 



Examples of virulent and rampant general 

 action are afforded by finger and toe in turnips, etc., 

 where the roots are invaded by PlasnwdiopJwra, 

 which induces hypertrophy and rotting of the 

 roots ; and by the damping off of seedlings, where 

 the fungus Pythhun rapidly invades all parts of 

 the seedlings and reduces them to a water-logged, 

 I)utrefying mass; or the potato-disease, which is due 



