388 Journal of Agricultural Research voi. xix. no. s 



varieties, soaked lo minutes in water, drained, and kept moist for 12 

 hours, with periodical weighings after blotting ofif all surface water each 

 time. The excess weight above 10 gm. represents the amount of water 

 absorbed. The curve rises rapidly in the first 3 hours, then slows down 

 somewhat to a more gradual rise. At the end of 6 hours, about 30 per 

 cent by weight of water has been absorbed; during the next 6 hours, 

 about 10 per cent more is absorbed. The 6 hours' presoaking, as prac- 

 ticed, consequently impregnates the cell walls and cells of the seed with 

 water, increasing the size and adding about 30 per cent by weight to the 

 seeds. The next 6 hours' treatment with water containing formalin in 

 solution adds only one-third as much more; and the formalin solution 

 as it diffuses into the seeds is consequently greatly diluted by 

 the amount of water already present in the tissues. Moreover, the 

 amount of formalin solution which can enter the tissues in the 6 hours 

 after presoaking is only one-third of what enters during a 6-hour formalin 

 treatment without presoaking. Should the subsequent formalin treat- 

 ment last much longer than 6 hours, an equilibrium would finally be estab- 

 lished between the strength of solution within the seeds and that on the 

 surface, resulting in both cases in a solution weaker than the original, in 

 accordance with the laws of diffusion of dissolved substances. Removing 

 the presoaked seeds after 6 hours' formalin treatment leaves them with a 

 solution content considerably more dilute than that finally present in 

 air-dry seeds directly treated with the full-strength solution; conse- 

 quently the weakened solution within the presoaked seeds resulted in 

 a very marked decrease in seed injury, as observed throughout the 

 experiments. 



As for the stimulation observed in presoaked seeds, this may be due 

 partly or wholly to the well-known stimulating effect of a toxic agent 

 in minimum dose, such as would finally be present in the presoaked seeds. 



In considering the effect of the presoak method on the blackchaff 

 bacteria on the seed coat, the dominant factor involved is the established 

 principle that microorganisms in an active vegetative condition are 

 more susceptible to the action of destructive agents than when dormant. 

 Presoaking the seeds, and consequently the bacteria on them, for a period 

 of six hours at room temperature causes the bacteria to begin to resume 

 vegetative activity before seed germination commences, because the 

 moisture and temperature conditions are ample for bacterial growth and 

 division to begin during this period. Subsequently exposed to the di- 

 rect action of the fonnalin solution applied full strength to the surface 

 of the seeds, the bacteria are naturally much more susceptible to destruc- 

 tion in this active condition. As a result, the disinfectant must act 

 with greater efficiency than in the usual treatment, where it acts on 

 dried and dormant bacteria. The six hours' presoak, on the other hand, 

 is not sufficient to cause wheat-seed germination, which would produce 

 a condition extremely susceptible to formalin injury. 



