29 



in the laboratory in which three slant tubes of prune agar were com- 

 pletely covered with powdered sulphur, lime and charcoal respec- 

 tively, and then inoculated with portions of the Drop mycelium. In 

 each experiment the mycelium grew over the coating of the sub- 

 stance as profusely as in normal cultures wherein no such substances 

 were employed. The experiments show conclusively that lime, char- 

 coal and sulphur utterly fail as a remedy for the Drop, even when 

 put on the soil thick enough to form a considerable covering. 



TJje success with which the fumes or gases given off from certain 

 substances are being used as insecticides has suggested the trial of 

 similar methods for treating destructive fungi in the greenhouse and 

 this has been tested especially with regard to lettuce diseases. The 

 value of such a method, if it could be applied with success,, is very 

 easily seen, as in treating a house between crops no limit need be 

 placed upon the strength of the gas employed. It is quite essential 

 however that in treating houses for the Drop or Rhizoctonia, which 

 thrive in the soil, that not only must the gas be fungicidal in its 

 effects, but that it possesses sufficient power of penetration to per- 

 meate the soil to a considerable depth and exercise its destructive 

 action. Could such a gas be j^roduced in an economical and prac- 

 tical way it would be of inestimable value to all growers of green- 

 house plants. It is not difficult to tind a considerable number of 

 gaseous substances which have strong fungicidal properties and 

 which may also be readily and cheaply produced. To choose 

 among these it is essential to find out especially their relative effects 

 upon fungi and plants, (the most desirable combination being, of 

 course, a maximum of the former with a minimum of the latter) and 

 their ability to penetrate the soil. Upon these features depend their 

 value as greenhouse fungicides. 



HYDROCYANIC GAS. 



This sas was first chosen for trial on account of its extensive use 

 as an insecticide. For such purposes it is often used with living 

 plants in the greenhouse, though occasionally with serious damage. 

 It is also used very extensively in fumigating nursery stock and in 

 various other ways for fumigating against insects. It is a deadly 

 poison to all animal life, causing almost instantaneous death when 

 inhaled in any quantity. This gas is produced by treating cyanid 



