no 



Journal of Agricultural Research voi. xviii, no. a 



has not found that the sand had any marked influence when the same 

 solutions are compared in sand and solution cultures. Wolkoff {36) 

 confirms this point of view in general, although he finds that ammonium 

 sulphate ((NHJjSOJ exhibits somewhat anomalous behavior. 



During the present investigation a immber of experiments were made 

 relating to this question. Freezing-point determinations were made on 

 nutrient solutions and on sand to which the solutions had been added 

 to give the sand a moisture content of 1 5 per cent. Also solutions were 

 allowed to stand in contact with the sand for long periods, conductivity 

 determinations being made at intervals. 



TABI.E XV. 



-Effect of sand on freezing-point depression and conductivity of nutrient 

 solutions 



From the data given above there is no indication that the sand has 

 appreciably altered the added solutions. To what, then, may discrepancies 

 between sand and water cultures be ascribed ? In the first place, a much 

 more extensive root development takes place in the presence of the solid 

 particles. This might in itself imply a different type of absorption, 

 though plants in solution cultures are capable of sufficient absorption 

 quantitatively under suitable conditions. Diffusion in water cultures is 

 very rapid but must be somewhat retarded in sand culture. For this 

 reason in the very early stages before an extensive root system has been 

 formed solution cultures may be superior to sand cultures, while later the 

 conditions may be reversed. Aeration is another factor which is different 

 in the two cases. Hall and Underwood (13) claim that this is the chief 

 difference between sand and water cultures. It is also conceivable that 

 the larger root system of sand cultures might affect the growth of tops'by 

 the formation in the roots of a greater quantity of some substance 

 accelerating growth. And finally, since even pure sand is not entirely 

 insoluble, a greater supply of silica is available to the plant in sand culture. 

 The exact effect of this is of course not known. 



As a matter of fact, in our experiments no very striking differences are 

 observed between sand and water cultures although it has generally been 

 true that taller plants with a greater number of tillers are produced in 

 sand cultures. Somewhat lower concentrations are inhibitive in solution 

 cultures, though the magnitudes do not vary greatly, and the differences 



