Action of Chemicals on Potato -Tubers. 287 



Experiments 7 and 8 — imsteeped controls. 



After four days' immersion, specimens (five tubers in each 

 instance) were removed from experiments 1, 2, 3 and 6, and 

 separately '' forced '' — i.e., placed under favourable conditions of 

 temperature (65° to 70°F.), and humidity for the develop- 

 ment of the causal fungus and its characteristic fructifications. 



It is to be noted that in all these forcing tests the necessary safe- 

 guards against possible cross-infection were taken. 



After ten days' immersion a second series of forcing tests 

 was instituted, ten tubers from each experiment being separately 

 forced, and subsequently investigated after expiration of 12, 

 24 and 28 hours. Included in this second series of tests were 

 two untreated lots of tubers which served as controls. Of these 

 one (a) was drawn from the same bulk as experiments 1-6, 

 while (b) was derived from another source. The chief object 

 aimed at in duplicating these control-forcing tests was to 

 demonstrate beyond all reasonable doubt that the condition of 

 experiment under which the " forcing " tests were carried out 

 was such as to induce the active development of the hibernating 

 mycelium which a previous trial of like material had also shown 

 to be present. 



The forced material was subjected to searching microscopical 

 examination, and the results' are briefly synopsised in the table 

 beneath. Where obvious and undeniable evidence of the 

 development of the blight fungus was demonstrable (experi- 

 ments 7 and 8) is indicated by a plus (-f-) sign, where no sign 

 of its presence was detected (experiments 1-6) a negative sign 

 ( - ) signalises the fact. 



Expt. * Treatment Results of forcing- tests 



Material steeped in ■.. 4 da> s 10 days 



1 0.25 per cent, phenol solution .. _ . _ 



2 0.25 per cent, formalin solution _ _ . — 



3 1.0 per cent, boracic acid ... - — - — 



4 4.0 per cent, boracic acid ... - — - — 



5 15 per cent. NaCl 1 per cent. 



bor. acid solution ... ... - - - — 



6 Plain tap water ,. .. ... - — - — 



7 Control a ... - — - + 



8 Control b - - - + 



