3° 



of potash with sulphuric acid ; the gas being given off when these 

 two substances are combined. In these experiments it was first 

 tested in its eiTects upon the spores of various fungi in open air. A 

 tight case containing about 8 cu. ft. was used into which was put a 

 glass slide bearing a drop of water with the spores to be tested. 

 The production of the gas was then started and the case closed for 

 the desired length of time, after which the slide was placed in a 

 moist chamber and the spores observed at intervals as to their ger- 

 mination. In all cases the results were checked by means of 

 untreated slides. A well marked fungicidal efTect of the gas was 

 ■evident, and where 20 grams of potassium cyanid were combined 

 with 40 grams of sulphuric acid diluted with 20 cubic-centimetres of 

 water the spores of Botrytis vulgaris were killed when exposed to 

 the gas for so short a period as fifteen minutes. In the experiment 

 where 10 grams of potassium cyanid were used, the Botrytis spores 

 failed to be killed after forty minutes exposure, although germination 

 was almost entirely prevented. When 20 grams of cyanid were 

 used, tube cultures of the " Drop " fungus (Sclerotinia) were exposed 

 to the gas and were found to be readily killed with about the average 

 exposure required for the spores. This shows, therefore, that the 

 lettuce-attacking-fungi, or their spores, can be killed with cyanid 

 gas when freely exposed to it. There remains to be considered its 

 effect upon plants and its power of penetrating the soil. The first 

 point was readily determined by placing plants in the case during 

 the treatment and in this connection it may be stated that they were 

 invariably killed. Furthermore a test was made of spores of the 

 carnation rust from plants which had been nearly killed by an over- 

 dose of the gas used as an insecticide, and it was found that they 

 germinated freely. 



In regard to penetration of the soil the following tests were made : 

 Spores of Botrytis were placed in a drop of water within a glass cell 

 on a slide and a strip of coarse cheese cloth fastened over the top to 

 keep out the dirt. The slides thus prepared were then buried rather 

 loosely in a box of fine loamy soil and the whole exposed to the gas 

 in the closed chamber. Depths of ^, r, i^, and 2 in. were tried, 

 both in dry and wet soil. With an exposure of from one to several 

 hours, using 20 grams of cyanid, no effect whatever could be 

 detected. It was plainly evident that the gas did not penetrate the 

 soil to any appreciable extent. Tests were also made with the Drop 



