Nov. i, 1920 



Effect of Drying Disinfected Seed Wheat 



223 



intervals 25 seeds were removed and germinated, with the results shown 

 in Table VI. 



Table VI. — Percentage of germination of wheat kept in contact with powdered para- 

 formaldehyde a 



Length of contact. 



i^hours 



24 hours 



2 days 



3 days 



5 days 



6 days 



8 days 



14 days 



20 days 



42 days 



Control . 



Experi- 

 ment 1 , 

 Little Club, 

 harvester- 

 thrashed. 



80 

 5° 



Experiment 2, 

 Little Club. 



Harvester- 

 thrashed . 



5° 

 30 



Hand- 

 thrashed. 



OO 

 00 



70 



Experiment 4, Early 

 Experi- I Baart, hand-thrashed. 



ment 3 , Eai - 



ly Baart, 

 hand- 



thrashed. Uninjured. 



100 

 80 



3° 



o 



Seed coats 



broken over 



embryo. 



90 

 80 



80 

 70 



30 

 20 



IO 

 O 



a No germination tests were made at the intervals represented by blank spaces. 



The data in Table VI show that dry paraformaldehyde powder kills 

 seed in contact with it, even those with unbroken seed coats. Those 

 with the testa injured, either by the thrashing machine or by breaking in 

 the laboratory with a needle, were injured and killed most quickly, as was 

 to be expected. It is noteworthy that the appearance and progression of 

 the seed injury was similar to that previously noted as occurring in the 

 successive germinations of treated seed being dried. The first sign of 

 injury was the retardation of the development of the plumule, which 

 became gradually more extreme. Finally, it was so injured that it did 

 not elongate at all after emerging from the seed, the sheath breaking 

 prematurely and showing the same curved, sickle-shaped deformity 

 previously found so characteristic of dried formaldehyde-treated seeds. 

 As it would be difficult to conceive of any absorption of solid para- 

 formaldehyde, the only plausible explanation of such "paraformalde- 

 hyde injury" is the penetration of formaldehyde gas through the seed 

 coat, the gas being concentrated in the interstices of the powder as a 

 result of the evaporation of the latter. Later experiments in which it 

 was found that absolutely dry seeds were uninjured by formaldehyde 

 fumes make it appear probable that the gas is dissolved in the cells of the 

 seeds and really diffuses into them as a solution. 



HUMIDITY AS THE DETERMINING FACTOR IN SEED INJURY 



The first hint that the humidity of the atmosphere surrounding the 

 seeds at the time of drying determined the amount of seed injury from 

 treatment with formaldehyde — by controlling the evaporation of the 



