THE INJURIOUS EFFECT OF FORMALDEHYDE 

 GAS ON POTATO TUBERS.* 



F. C. STEWART and W. O. GLOYER. 



SUMMARY. 



In treating a quantity of seed potatoes with formaldehyde gas 

 for scab at the Station in the spring of 1912, many of them were so 

 severely injured that they were unfit for seed. The injury took 

 the form of sunken brown spots surrounding the lenticels and eyes. 

 The gas was generated by the permanganate method, using the 

 standard formula of 3 pints of formaldehyde solution and 23 ounces 

 of potassium permanganate to each 1000 cubic feet of space. An 

 investigation into the cause of the injury placed the blame chiefly 

 upon the small quantity (1.5 lbs.) of potatoes per cubic foot of space 

 in the fumigation chamber. The high relative humidity of the air 

 and the sprouted condition of the potatoes were important accessories. 

 By the property of adsorption the potatoes seize and hold the for- 

 maldehyde gas upon their surface. If there are but few potatoes 

 they adsorb so much gas that the tissue is injured; but when the 

 gas is distributed over a large quantity of potatoes it does not 

 gather at any point in sufficient quantity to cause injury. In our 

 experiments various degrees of lenticel spotting occurred with all 

 quantities up to 12 lbs. per cubic foot, but no eye injury appeared 

 when 5 lbs. or more per cubic foot were used. The effect of lenticel 

 spotting on germination and growth have not been fully determined, 

 but it is believed that there may be considerable lenticel spotting 

 without material injury to the tubers for seed purposes. The gas 

 treatment is to be recommended only in cases in which the liquid 

 treatment is impracticable. With the gas treatment it is evident 

 that in order to secure uniform results the quantity of the chemicals 

 must be varied according to the quantity of potatoes per cubic foot 

 of space, but further experiments are required to determine just 

 how it should be done. At present, the only formula which can 

 be recommended as being both safe and efficient for scab is that 

 of 3 pints of formaldehyde and 23 ounces of permanganate to 

 167 bushels of potatoes in 1000 cubic feet of space. 



* Reprint of Bulletin No. 369; for Popular Edition, see p. 774. 



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