Nov. i, 1920 Effect of Drying Disinfected Seed Wheat 231 



hyde gas constantly formed next to the seed by its decomposition would 

 be determined by the moisture in the seed coat. It would follow, as was 

 actually found, that there would be a point where maximum seed injury 

 would occur — at a humidity low enough to permit the solid polymer to 

 form on the seed as the solution evaporates, yet high enough to permit 

 diffusion in solution of the gas formed from it through the cells of the seed 

 coat to the embryo. Thus may be explained the gradual lessening of 

 the degree of injury from the point of maximum injury to practically 

 normal germination in dry atmospheres. 



The work of Arcichovskij (1) on the effect of graded concentrations of 

 formaldehyde solutions ranging from 0.125 to 40 per cent supports the 

 assumption that the ease of penetration of formaldehyde is dependent on 

 the dilution of the solution as it passes through the cells into the seed. 

 He found that, for any given duration of exposure, seed injury did not 

 increase directly with the concentration of the solution. After a definite 

 point of maximum injury, the harmful action of the solution decreased 

 with increased concentration, until in all exposures over four hours the 

 undiluted 40 per cent formaldehyde solution caused less injury than the 

 0.125 per cent dilution. For instance, after 256 hours 37.5 per cent of 

 the seeds from the 40 per cent solution germinated, while those in the 

 0.125 per cent solution were entirely killed after 32 hours' exposure. 

 The curve he has drawn showing the relation between concentration of 

 the solution and the percentage of germination is similar to the curves 

 in this report which show the relation between humidity and formalde- 

 hyde injury to seeds upon drying after treatment. 



The preceding paragraphs merely offer a suggestion of an explanation 

 of the observed facts. This interpretation of these facts is based on 

 several assumptions which have not been proved by direct evidence. 

 One is that paraformaldehyde, as a solid, does not injure seeds but only 

 upon its breaking down into formaldehyde gas and forming a toxic vapor 

 about the seed. Another is the assumption that this formaldehyde does 

 not penetrate seed coats as a gas but that it must enter in solution. 



It should be pointed out here that in experiment 2 the maximum injury 

 occurred in the atmosphere of 70 per cent humidity (Table VIII) in the 

 desiccator in which it was found that the formaldehyde solution evapo- 

 rated to dryness without the formation of paraformaldehyde (Table IX). 

 This indicates that seeds may be injured by the concentration of a o. 1 

 per cent solution on the surface as evaporation proceeds, without the 

 formation of the solid polymer. 



RELATION OF DEGREE OF INJURY TO MANNER OF DRYING 



In the course of the experiments it was noted that the drying injury 

 was not always of the same severity, and it was finally found that it 

 depended on the aeration of the drying sample, thinly spread seed escap- 

 ing the injury suffered by that dried in heaps. This observation was 



