Nov. i, 1920 Effect of Drying Disinfected Seed Wheat 233 



of the solid which when evaporated in a space of 2 ,400 cc. checked by its 

 partial pressure further decomposition of the sample is not shown. It 

 would appear to be approximately o. 1 gm., the average decrease in weight 

 found upon successive weekly weighings of the inclosed sample. The 

 slight fall of the curve for this period in the desiccator is explained by the 

 fact that when the dish was removed each time for weighing the con- 

 centration of gas within would be diluted and so the sample would con- 

 tinue to lose weight. A parallel control experiment gave the same curve 

 and the same total loss in weight, 0.21 gm., during the two weeks in the 

 desiccator. 



The significance of this curve for the problem of post-treatment injury 

 of dried seeds is that when there is no aeration the formaldehyde gas 

 from the evaporating paraformaldehyde on the seeds easily saturates the 

 atmosphere in the interstices of the sample and inhibits the evaporation 

 of more of the solid. The slower the outward diffusion of the gas the 

 longer will the paraformaldehyde remain on the seed surfaces and the 

 longer will a toxic atmosphere exist about them. As the penetration of 

 the seed coat and subsequent injury by formaldehyde is comparatively 

 slow, usually occurring in from 3 to 5 days with a 0.1 per cent solution 

 (Table VII), it is entirely conceivable that with rapid drying and thinly 

 spread seed any paraformaldehyde formed can be completely evaporated 

 and its dissipation effected so rapidly that it can not enter and injure the 

 embryo. 



Seeds treated with a 0.2 per cent solution, twice as strong as the usual 

 treatment, were dried without injury when spread in a single layer on 

 towels, while such seeds dried in quantity in an open box were prac- 

 tically all killed. That it was the time required for the formaldehyde to 

 penetrate the testas which saved the former lot of seed was shown by the 

 fact that some of the same sample which had the seed coats broken over 

 the embryos were dried beside the others and were severely injured after 

 24 hours. In the former case the paraformaldehyde evaporated and 

 diffused before it could penetrate the sound seed coat. But when a 4.5 

 per cent solution was used, even the seeds with unbroken coats were 

 found to be injured after 24 hours' drying under these conditions. The 

 quantity of paraformaldehyde formed presumably was too great to 

 escape before seed injury occurred. The broken seeds dried at the same 

 time showed proportionately greater and more rapid injury than the 

 broken seeds treated with the weaker solutions. It will be noted in 

 Table X that embryos exposed by broken testas are not injured by a 

 10-minute dip into formaldehyde as strong as 0.2 per cent but that a 

 4.5 per cent solution is injurious. It is significant that with rapid drying 

 and aeration even the seeds with broken seed coats were not injured by 

 a o. 1 per cent solution. Yet it has been found repeatedly that when 

 perfect seeds thus treated are dried without aerating they are injured or 

 killed. 



