508 BROOKLYN BOTANIC GARDEN MEMOIRS 



these most dilute solutions is higher than is the case of those originally- 

 having a greater salt content, seeming to indicate that at this extreme 

 dilution the plants are not only forced to yield ions to the solutions 

 but are unable by reabsorbing them to reduce the concentration to a 

 point lying much below the equivalent of 50 grm. norm, in a million 

 liters. 



As the original concentration of CaS04 is increased to 31.3 and 

 52.1 grm. norm, respectively absorption increases to a point showing 

 .net gains by the plants. Leaching of ions by the plants, if it takes 

 place, is more than met here by their greater absorptive activity. 

 This activity when greatest reduces the residual ion content markedly 

 below that seen in the case of the originally more dilute solutions. 

 It seems that with the addition of even slightly larger quantities of 

 CaS04, the absorptive function becomes more active and is able more 

 nearly to exhaust the quantity of ions offered. 



As the quantity of CaS04 is increased to concentrations rising 

 from 101.9 to 824.4 grm. norm, in a million liters the plants reduce 

 the ion content of all solutions but absorption even at its greatest 

 leaves a residue which increases as the quantity offered increases. 

 Absorption, while in general increasing as the quantity of ions present 

 increases, lags far behind the quantities offered. It thus comes about 

 that the curve representing the residual ion content approximately 

 parallels that representing the original ion content of the solutions. 



From these data it would seem that when squash seedlings are 

 grown in darkness at 18° C. in solutions of CaS04 alone, they are 

 unable to absorb as many ions as they lose when the solution contains 

 less than about 30 grm. norm, of the salt in a million liters. When the 

 solutions contain somewhat more than this quantity of this mixture of 

 ions the plants can reduce the more dilute members of the series to an 

 ion content of about the concentration seen at this equilibrium point. 

 When the supply of ions is far in excess of absolute requirements, the 

 seedlings absorb greater quantities than in weaker solutions but the 

 quantity of residual ions left in the solution increases in nearly the 

 same proportion as the quantity offered. 



In the following table (Table 2) are shown (i) the original con- 

 centration of each solution, indicating the quantity of ions offered 

 in each case; (2) the concentration of each solution at the time of 

 maximum absorption, or the residual ion content of each solution and 

 (3) the quantity of ions absorbed from each solution at the time of 

 maximum absorption. 



