New York Agricultural Experiment Station. 211 



Another possible factor is the position of the tubers in the dis- 

 infection room. In most of our experiments the test tubers lay on 

 the floor of the disinfection chamber. Also, in the original case of 

 injury the crates of potatoes were all near the floor. Are tubers 

 on the floor more, or less, liable to injury than tubers near the ceiling? 

 According to Mayer and Wolpert 37 the concentration of the for- 

 maldehyde gas decreases from the ceiling downward and more 

 thorough disinfection occurs at the ceiling than at the floor. In the 

 single experiment (No. 23) conducted by us tubers on the floor were 

 quite as severely injured as those near the ceiling. 



Morse's caution to avoid placing tubers directly above the generator 

 appears to be well founded. In one of our Experiments (No. 1) 

 two tubers suspended in a wire basket 6| in. above the generator 

 were much more severely injured than tubers on the floor of the 

 disinfection chamber. However, this can not have been a factor 

 in the cellar experiment because none of the potatoes were above 

 a generator or nearer than 2.5 feet to one. Provided the tubers 

 are not over the generator it does not matter how near they are 

 to it. In our experiments the generator was a pint tin cup. It was 

 observed repeatedly that tubers lying on the floor within one inch 

 of the generator were no more injured than those in the farthest 

 corner of the chamber. 



Any break in the skin of the tuber increases the liability to gas 

 injury at that point. When pins are stuck into the tubers before 

 treatment a sunken area of dead brown tissue appears around each 

 pin. However, we believe Wollenweber to be in error when he says 

 that the effect of formaldehyde is a test as to whether or not the skin 

 is wounded. 38 If that be true there is no such thing as an unwounded 

 potato because any potato treated with formaldehyde gas in the 

 manner we have described will show the sunken, dead, brown spots. 



That the gas enters by way of the lenticels is very plain in some 

 cases and obscure in others. On potatoes grown in wet heavy soil 

 the lenticels become abnormally developed. When the tubers are 

 first dug such lenticels are plainly visible to the unaided eye as 

 small white specks and they are readily detected even after the 



37 Mayer, E., und Wolpert, H. Beitrage zur Wohnungs-desinfektion durch For- 



maldehyd. Hyg. Rundschau 11 : 157. 1901. 



38 Wollenweber, H. W. Studies on the Fusarium problem. Phytopathology 3:43. 



1913. 



