ANTHRACNOSE OF CUCURBITS. 



61 



is of interest to note that the 1915 seed was apparently as free from 

 disease as treated seed. All of the treatments appear to have been 

 effective in these field tests. 



The effectiveness of formaldehyde, 1 per cent for 20 minutes, and of 

 mercuric chlorid, 1 to 1,000, for 5 minutes, was tested in the laboratory 

 by avoiding contamination after sterilization and planting the seed 

 in culture media. One test was made on seed previously inoculated. 

 In all cases, however, the effect upon the normal surface flora of the 

 seed was used as a criterion. The results of these tests are presented 

 uuTable XI. 



Table XI. — Laboratory tests of the treatment of cucumber seeds with mercuric chlorid and 

 formaldehyde for the control of anthracnose. 





Date, 

 1917. 



Method. 



Mercuric chlorid. 



Formaldehyde. 



Seed used. 



Num- 

 ber 



tested. 



Results. 



Num- 

 ber 

 tested. 



Results. 



Ohio 



Apr. 9 

 ...do 



2 per cent dex- 

 trose agar, in 

 plate. 







20 

 20 

 40 



10 sterile; 1 with fim- 

 gus; 9 with bacteria. 



4 sterile; 4. with fungi; 



Inoculated 



20 

 30 



10 



16. 





on Mar. 

 13,1917. 

 Do 



May 13 



.. ..do 



All sterile except one; 

 anthracnose oli coty- 

 ledon. 



9 sterile; 1 developed a 

 fungus. 



12 with bacteria; no 

 anthracnose. 

 None sterile; 7 with 



Do. . . 



Bouillon tubes . . 

 Nutrient agar . . . 



fungi; no anthrac- 

 nose. 



Do 

















These results show that the mercurie-chlorid treatment is more 

 reliable than the formaldehyde in absolute effectiveness. The very 

 interesting case in which 1 out of the 136 inoculated seeds yielded 

 a diseased seedling deserves some comment. The age and location 

 of the lesion indicated that it had resulted from a recent spore infec- 

 tion rather than an earlier micropylar invasion. This would mean 

 that the spore had not only escaped the germicide but had also 

 survived two months of desiccation. It was probably lodged in 

 the micropyle and -protected from the .germicide by an air bubble. 



Owing in part, no doubt, to organic matter on the seed, there is a 

 marked decrease in the strength of mercurie-chlorid solutions after 

 seed is immersed therein. Six liters of seed decreased the concen- 

 tration of mercuric chlorid in eight liters of the germicide by almost 

 one-half. This means that the solution can be safely used only 

 once or twice. 



The effectiveness of a 5-minute immersion in weaker solutions has 

 been tested by the agar-plate method. Using about 100 seeds for 

 each series, the following percentages of sterile seeds were obtained: 



Mercuric chlorid, 1 to 1,500.. 99 per cent sterile. 



Mercuric chlorid, 1 to 2,000 94 per cent sterile. 



Mercuric chlorid, 1 to 3,000 97 per cent sterile. 



