306 NINETEENTH REPORT. 



the fungus spores can tolerate direct sunlight for at least a period of 

 two liours and ten minutes. Several cases of contamination occurred, 

 but these did not interfere with the results, as the experiment was run 

 in triplicate. 



EXPERIMENTS DEALING WITH THE TOXIC SUBSTANCE PRODUCED BY THE 



FUNGUS. 



Historical Introduction : 



Our knowledge of tliat biological adjustment wliich makes an organism 

 parasitic, and restricted, quite often, to only one host, is as yet very 

 indefinite. Research in this vast field is only in the beginning stage, 

 though some fundamental studies have already been made. 



DeBary's (1886) epoch making research with Sclerotinia libertiana, 

 was probably the first fruitful attempt to determine the nature of parasit- 

 ism. Those who followed him proceeded along the path he opened. 

 Most of the investigations seem to have been directed toward the cytolytic 

 activities of the fungus upon the host. While the demonstrations of the 

 destruction of the cell wall or its cementing substance by lytic enzymes 

 may be considered the first work necessary in the study of parasitism, 

 such studies fail to explain the subsequent killing and disorganization 

 of the protoplasts. It must also be remembered that the cellulose walls 

 are for the most part non-living, and again, these walls being porous 

 would not be marked impediment to any osmotic or toxic activity of 

 fungus secretions upon the plasma membrane. Nor does the fact that 

 specific enzymes have been demonstrated both within the cells of certain 

 fungi and in the dead tissues of the hosts which they parasitize, explain 

 what actually causes the killing of the cells. DeBary has shown for 

 S. libertiana that the fungus must kill the host cells in advance of growth, 

 and that it is the disintegration products of the dead cells whicli provide 

 food for the fungus. He also suggested that the oxalic acid found in 

 connection with the fungus might be the toxic principle. Among the 

 contributions which followed DeBary's we find Marshall Ward's dealing 

 with a Botrytis disease of lily (1888). He confirmed DeBary as to the 

 presence of cytolytic enzyme, but contributed nothing further toward our 

 knowledge of the toxic principle. Later, follow in quick succession, the 

 work of Behrens (1898), Nordhausen (1899), and Smith (1902), deal- 

 ing with the parasitic nature of Botrytis cinerea. Smith concluded that 

 oxalic acid is the toxic principle. However, Brown (1915), in a recent 

 paper, has proven conclusively that neither oxalic acid nor oxalates con- 

 tribute to the lethal principle of the fungus extract. Brown has also 

 made marked advance in that he has established a quantitative basis of 



