230 



Journal of Agricultural Research 



Vol. XX, No. 3 



in atmospheres of such moisture content as permit the formation of 

 paraformaldehyde in evaporating solutions, is greatest in intermediate 

 humidities, becoming less as the moisture percentage decreases. This 

 is in spite of the fact that there is an increase in the quantity of para- 

 formaldehyde formed in these successively lower humidities. Secondly, 

 the degree of injury to untreated seed placed in desiccators alongside 

 of evaporating formaldehyde solutions in closed chambers is least in the 

 driest atmosphere and increases with increased humidity. It therefore 

 seems probable that the seeds in the lower humidities were so dry that 

 penetration of the seed coat by formaldehyde was difficult because of 

 the lack of sufficient moisture to permit solution of the gas on or in the 

 testa and its subsequent diffusion to the embryo. 



Table IX. — Relation of the humidity of the atmosphere to the evaporation of formalde- 

 hyde solutions, the formation of paraformaldehyde, and the effects of the fumes on un- 

 treated wheat 



In presenting this explanation, we are assuming that formaldehyde 

 does not penetrate seed coverings easily, if at all, as a gas but must be 

 dissolved. A small quantity of moisture in the cells of the seed covering 

 therefore would perhaps be necessary to permit injury from formaldehyde 

 fumes. This is consistent with the statement of Humphrey and Potter 

 (7) that— 

 disinfection with formaldehyde gas seems to require some moisture. 



This supposition would explain the relation found between the degree 

 of injury resulting from drying treated seed and the humidity of the at- 

 mosphere in which the seed is dried. With the atmosphere sufficiently 

 dry to allow the formation of the "formaldehyde reservoii " — the coating 

 of paraformaldehyde on the seed — the ease of penetration of the formalde- 



