402 BOTANICAL GAZETTE [may 



also that chemical reaction enters in the case of the common types of 



garden soil. 



We come finally to a consideration of the effects of bog toxins 



upon soils. It is to be noted that the poisonous action of bog toxins 

 is more harmful when the plants are immersed in the solution, than 

 when grown in the contaminated soil cultures. That the poisonous 

 matter injurious to plant growth is present in the soils used as filters 

 is seen upon comparison with the controls. Manifestly, the theory 

 of lack of 2 in bog water or in bog soils as the cause of xerophily is 

 not satisfactory to account for the results, because water cultures 

 usually have less 2 than any soil medium. The transpiration data 

 for boiled bog water (Table I, page 393) are further evidence in this 

 direction. The inadequacy of the theory of low substratum tempera- 

 ture is, for this locality, equally obvious. That the action cannot 

 be attributed to large amounts of dissolved substances has been 

 shown in the determination of the osmotic pressure of bog water in 



The garden soils contain a much 



5 



larger amount of nutrient ingredients than bog water, and hence the 

 presence of those salts should tend to increase the growth-rate. No 

 such increase in activity occurred. The length of time during whic 1 

 the wheat plants were allowed to grow is palpably insufficient to 

 "exhaust" or contaminate the soils. The retardation seen in the 

 contaminated soils is lacking the corresponding normal average in 



8 per cent., 3 P er cent ' and 3 



amount of 1 



per cent, for quartz, clay, and humus respectively. From the res s 

 it may be concluded that the adsorption and retention capacity soi^ 

 for toxins is generally higher the greater its content of humus, t wa^ 

 shown elsewhere that a bog-water solution well aerated, or up 

 long standing with exposure to air, lost its injurious P ro P e ' * e 



When plants are grown in this oxidized solution it is found tna 



i.u TVip<;p results 

 solution becomes decidedly beneficial to plant growth. 1 ne& 



are also obtained with the contaminated soils. When first use ^ 

 exert a distinctly injurious effect. If the amount of water tra - ns ^ 

 by the plants is replaced by bog water, the soils become "^.^j 

 Decrease in toxicity always follows aeration of the soil an ©^ 



and since the physical conditions mainly determine the a ™°^ [ty 

 oxidation, these are of greater consequence in restoring 

 to the soil. 



