536 University of California Publications in Agricultural Sciences [Vol. 1 



hence it may manifest distress and weakness which nnder nat- 

 ural conditions might be quite impossible. Owing to osmotic 

 influences, the plant would lose salts and otluT substances to the 

 distilled water more quickly and in larger quantity than to tap 

 water or to a balanced solution. It would therefore be more 

 subject to weakening or to the absorption of toxic materials in 

 the former than in the latter medium. In otlier words, under 

 such circumstances copper, for example, would merely exagger- 

 ate the untoward conditions for plant growth, while it might 

 have no power to atfect the plant under more favorable condi- 

 tions. Again, seeds are not usually allowed to germinate in 

 the solution which is to be tested in the cultures, but in a medium 

 of a harmless nature. Does not sudden removal to salt-solution 

 cultures render them less immune to certain substances than if 

 they had been allowed to accustom themselves from the begin- 

 ning to a given salt ? 



We do not desire to give the impression from these arguments 

 that we deprecate the use of the solution-culture method. On 

 the contrary, we think it of great value in the study of many 

 fundamental problems and also for obtaining relative data. 

 When, however, one attempts to use it in drawing absolute 

 conclusions for purposes of application to such a subject as that 

 under consideration, it falls as far short of throwing light on the 

 actual effects of a given substance on plant protoplasm (as the 

 latter is situated under natural conditions), as does any other 

 method of study now employed. We believe that the contlicts 

 in the results just reviewed are perhaps explicable on one of the 

 bases above discussed ; and since no modification of the solution- 

 culture method is free from serious objection, we must accord 

 equal value to all results of reliable investigators. Consequently 

 we arrive at the conclusion that in the experiments above cited 

 there is no absolute evidence that copper is or is not stimulating 

 to plant protoplasm in solution cultures. While there appears 

 to be more evidence that copper is toxic under the conditions 

 and in the concentrations named than that it is stimulating, we 

 cannot admit that the plant has been tested in any two of 

 the experiments under essentially tlie conditions of its natural 



