1917] SOILS FERTTLIZERS. 213 



of washed quartz sand, supplied with a nutrient solution having an initial 

 total concentration of 1.75 atmospheres maximum osmotic pressure, but with 

 36 different proportions of potassium phosphate, calcium nitrate, and mag- 

 nesium sulphate. " The total growth period was 24 daj's, during which time 

 the total water loss from each culture was determined at the end of each 3-day 

 interval. At the end of the growth period the cultures were compared with 

 respect to (1) dry weight of tops, (2) dry weight of roots, (3) total water 

 loss, (4) water requirement per gram of dry tops, (.5) water requirement per 

 gram of dry roots, and (6) the ratio of the weight of tops to dry weight of 

 roots." 



It was found that " the graphs representing the growth rate of young wheat 

 plants for three preliminary series show a region of optimal growth rate lying 

 between the concentrations 1 and 2 atmospheres. With the initial total con- 

 centration about 1.75 atmospheres, the nutrient solution that produced the 

 greatest dry weight of tops also produced the greatest dry weight of roots. 

 This solution is characterized by having 0.2 of the total osmotic concentration 

 derived from KH2PO4, 0.7 from Ca(N03)2, and 0.1 from MgSO*. 



"A general comparison of the results from this sand-culture series with 

 solution cultures (Shive's) grown from the same lot of seed but at a different 

 time period brings out [that] (1) the average dry weights of both tops and 

 roots were decidedly greater for the plants grown in the sand than for those 

 grown in the soultions ; (2) the results obtained in the solution-culture series, 

 having a total osmotic concentration of 0.1 atmosphere, are more nearly like 

 those from the sand series than are the results secured from the more concen- 

 trated solution series (1.75 atmospheres), in which the solutions were of the 

 same total osmotic concentration as that employed for the sand cultures ; and 

 (3) there is a marked difference between the solutions producing the best de- 

 velopment of plants in sand and those giving the best growth in the solution 

 cultures with respect to the osmotic proportions of the three salts employed. 

 A comparison of the results from these two series, the one grown in solution 

 and the other in sand cultures, furnishes evidence for the conclusion that se- 

 lective adsorption plays an important role in bringing about the observed 

 physiological differences. The sand-culture solutions giving low yields of tops 

 are characterized by a wide range in the Mg/Ca ratio, a very wide range in 

 the Mg/K ratio, and a narrow range in the Ca/K ratio value. The solutions 

 giving high yields of tops show a narrow range in the Mg/Ca ratio and a com- 

 paratively wide range in both the Mg/K and Ca/K ratio values. The data 

 presented support the conclusion of earlier workers to the effect that the total 

 transpirational loss from a plant culture is approximately proportional to the 

 growth made by the plants during the period of time considered. 



" The water requirement per gram of dry tops varies considerably with the 

 different proportions of the component salts. It appears that low water require- 

 ment for tops is associated with a low partial osmotic concentration of mono- 

 potassium phosphate, and that high water requirement is associated with high 

 partial concentrations of both magnesium sulphate and monopotassium phos- 

 phate. The water requirement per gram of dry roots is much higher than 

 the same value for tops. A consideration of the ratio of tops to roots brings 

 out the fact that in every instance a high water requirement corresponds to a 

 high ratio of tops to roots. Good growth of tops was found to be associated 

 with a high osmotic ratio of Ca(N03)2 to MgS04 and poor gi-owth of tops with 

 a low value of this ratio." 



A list of 46 references to literature bearing on the subject is appended. 



Preliminary investigations in comparison of field with, laboratory experi- 

 ments in soil biology, G. P. Koch {Soil Sci., 2 {1916), No. 1, pp. 8'i-92, fig. 1).~ 



