278 Report of the Department of Chemistry of the 



Taijle X. — Summary op Relation Between Dry Substance Produced and 

 K 2 Utilized in Plant-food Requirement Experiments. 



BARLEY, PEAS, TOBACCO, TOMATOES. 



COMMENTS ON RESULTS. 



The foregoing tables present results that are striking in their 

 uniformity and agreement. 



In considering these results it is not to be forgotten that they 

 were secured by the use of artificial soils much less complex in com- 

 position and reactions than natural soils. Moreover, the temperature 

 and water supply were under control and were regulated so far as 

 possible to meet more fully the plants' needs. Under these conditions 

 it may be held with some reason that the results of the experiments 

 are not applicable to outdoor conditions. It is hardly to be expected, 

 however, that such a difference in the environment of plants would 

 materially modify the processes of growth or cause new physiological 

 reactions. It is certain that, as shown in the next table, in most 

 instances the conditions permitted a growth of the plants that would 

 be satisfactory for field crops, the production of dry matter with 

 the barley in two of the three experiments being beyond what could 

 reasonably be expected in a farm crop. 



It is clearly shown that under the conditions involved no fixed 

 relation was maintained between the production of dry matter and 

 the amounts of phosphorus and potassium utilized. 



Up to a somewhat indefinite point the production of plant sub- 

 stance increased in most cases with the increase in the supply of 

 the variable constituent, but beyond that point the utilization of 

 both phosphorus and potassium compounds increased without any 

 consistent and well defined corresponding increase of plant 



