138 PLANT PHYSIOLOGY 



culture fluid and which may affect in a very dissimilar way two 

 different electrolytes. In this connection it is only necessary to call 

 attention to the toxic action of certain compounds of mercury, in 

 which increased toxicity, due to the presence of small amounts of 

 some other* salt of the same acid as the mercury salt used, is indeed 

 quite remarkable. Within the past few months an unusually inter- 

 esting paper has appeared in which Kanda reports the action of 

 certain toxic agents upon plants grown in pots as compared with 

 those plants grown in water cultures. His important conclusions 

 are as follows: (1) A strongly dilute copper sulphate solution, even 

 0.000,000,249 per cent, is injurious to seedlings of the common garden 

 pea in water cultures; and neither a solution ten times nor one a 

 hundred times more dilute produced any stimulative effect. (2) In 

 pot experiments with soil, the same seedlings are uninjured when 

 watered twice a week during a period of from five to eight weeks 

 with a solution of .249 per cent; in other words, even after from 

 five to seven grams of copper sulphate were present in each pot. 

 No explanation is offered of this remarkable diversity of action, 

 but within the past few months another paper has appeared which 

 may throw light upon the results given. True has ascertained that 

 finely divided paraffin, quartz-sand, filter-paper, or other insoluble 

 substances are all found to reduce the toxic action of the deleterious 

 salt. It is explained on the assumption of an absorption of the toxic 

 molecules by the surface of the insoluble particles. Increasing the 

 number of grains of sand, for instance, in any toxic solution pro- 

 duced the same effect as increasing the dilution. From the results 

 of these two papers it would seem, therefore, that we have two 

 entirely different sets of conditions to deal with when any test of 

 such action is made in water cultures, on the one hand, and in soils, 

 on the other. If Kanda's results are confirmed, an extensive series 

 of tests with both fungi and higher plants should be made in order 

 to determine some relation which may give a working basis for 

 further comparisons. In fact, much of the work thus far done will 

 have to be reexamined in the light of these results, for if any pre- 

 cipitate or other solid particles have been present in the solutions, 

 an error will enter into the calculations. The question will also arise 

 if the surface extent of the vessel used in the culture is of any con- 

 sequence. The practical bearing of these results in the treatment of 

 soils is a matter which may prove of unusual economic interest. 



Loew observed that marked injury results when such a plant as 

 Spirogyra is placed in a solution of a magnesium salt, or in a solution 

 in which magnesium is in excess. From all of the results obtained 

 Loe\v has inferred that there is present in all plants requiring cal- 

 cium an essential calcium protein compound. When magnesium 

 must, owing to the predominance of this element, be substituted 



