IK JURY BY DISINFECTANTS TO SEEDS AND ROOTS. 31 



The relative resistance of Firms ponderosa to the acid is probably 

 due to its rapid growth, as at Halsey. The severe injury to P. strobus 

 is rather surprising in view of the length of time which elapsed before 

 germination. The consistent relation in series 638 between the de- 

 crease in stand and the amount of acid used and the evidently helpful 

 effect of frequent watering leave no reasonable doubt as to the agency 

 of the acid in causing the decreased stand. In all of the series ex- 

 cept 631 the treated plats were uniformly poorer than the checks. 

 In series 638, fewer seedlings appeared in acid plats than in the 

 checks in all cases, the deficiency being greatest in the ordinary 

 watering plats, and the amount of death just after the seedlings came 

 up in the ordinary watering plats was very large. The amount of 

 germination and early loss for the other series was not determined. 



The evidence of the experiments at Morrisville as a whole shows 

 that at this nursery the amounts of acid necessary to cause injury 

 were much smaller than at Halsey. 



GENERAL DISCUSSION AND CONCLUSION. 



It is evident that the toxicity of disinfectants to the roots of plants 

 in soil at Halsey, Nebr., varies greatly in response to a number of 

 different factors. The amounts of water in different parts of the 

 soil at different times and the movements of soil water, which result 

 in concentrating the soil solution at particular points, must be con- 

 sidered, as well as the concentration of the solution applied. The 

 depth of the root tips in the soil at the time of greatest concentration 

 of the soil solution is also of prime importance, and the time of appli- 

 cation is a very important variable. 



In general, while it is evident that disinfectants do not act on plant 

 roots in soil to the same extent as in liquid cultures, they seem to 

 act in much the same way. If only the free poison in the soil solution 

 is considered, it is doubtful whether a great difference in degree of 

 toxicity can be found in soil and in liquid cultures. However, the 

 activity of poisons in the soil solution should not be expected to 

 equal their activity in pure water cultures. Antitoxic relations 

 which have been found by various workers to exist between numerous 

 substances in water cultures may be expected to exist between most 

 disinfectants and various components of the soil solution. An in- 

 vestigation of antagonism between substances obtained in soil ex- 

 tracts and some of the substances used in soil disinfection should 

 yield some interesting results. Most poisons are of necessity rather 

 unstable substances, and even where leaching is prevented, as in 

 pot experiments, and nonvolatile substances are used, the loss of 

 free poisons from the soil solution by combination with soil con- 

 stituents and by other absorptive processes is undoubtedly great. 



