PARASITISM IN FUNGI 139 



pointed out that the evidence is clear that the entrance of 

 the stoma by any germ-tube is no index of the capacity of 

 that germ-tube to infect the leaf. It is very gratifying to 

 note that this is in accordance with my statement on the 

 subject ; I made clear that my admitted proof of infection 

 having taken place was the production of fruit by the 

 fungus on the inoculated host-plant. When this did not 

 occur the experiment was put down as a failure. What 

 causes the entry of the germ-tubes was not discovered, but 

 probably a positively chemotropic substance as Miyoshi 

 and others have supposed. 



The second paper by Salmon shows that the conidia of 

 certain ' biologic forms ' of Erysiphe graminis can be 

 induced to infect leaves of host-plants which are normally 

 immune to their attacks after the vitality of the leaf has 

 been affected by cutting out a piece of its tissue, injuring 

 the leaf by touching it with the red-hot point of a knife, 

 cutting away half the thickness of the leaf, treating it with 

 either chloroform, alcohol, etc. In most instances infection 

 followed, and the fungus formed fruit on the injured parts 

 that is, it grew and fruited on the tissue that has been 

 injured. Salmon's summary of results on this point is as 

 follows : 



'(i) Susceptibility can be induced not only by various 

 kinds of mechanical injury, but also by such interference 

 with the normal function of the cell as follows the appli- 

 cation of anaesthetics and heat. 



'(2) The cpnidia of the first generation produced on 

 leaves of a strange host-plant previously subjected to the 

 action of alcohol, ether, or heat, retain the power of infect- 

 ing their original host, and do not acquire the power of 

 infecting normal leaves of their temporary host.' 



