230 SCIENCE PROGRESS 



also depends on the salt. Thus potassion is not absorbed with 

 the same rapidity by the same plant from different potassium 

 salts. The rate of absorption is also influenced by the in- 

 ternal and external conditions of the plant. It may occa- 

 sionally happen that in experiments extending over some 

 considerable time equivalent quantities of the constituent ions 

 of a salt may be absorbed ; but this is by no means always the 

 case, and generally when equilibrium is reached an unequal 

 absorption of ions has taken place. 



In some cases ions accumulate in the cell and pass in against 

 the apparent concentration gradient, while in other cases the 

 passage of ions into the cell is never sufficient to reach that 

 required for equality of distribution between the interior of 

 the cell and the external medium. This result has also been 

 obtained by Stiles and Kidd (loc. cit.), who have shown that 

 the extent of ionic intake depends on the concentration of the 

 salt and on its nature. Generally, with " nutrient " salts, the 

 '* absorption ratio " — that is, the ratio of final internal to final 

 external concentration — varies from many times unity with 

 low concentrations to a fractional value for high ones. 



A very curious observation is recorded by Pantanelli, to 

 the effect that when absorption is rapid, it is not continuous, 

 but that absorption is followed by partial excretion of the 

 same ion. Then fresh absorption follows, but less than the 

 first, then excretion takes place, then further absorption, and 

 so on, the whole process being comparable to the oscillations 

 of a damped pendulum whose amplitude gets less and less 

 with time. This phenomenon requires further investigation. 



As a consequence of unequal absorption of ions, it follows 

 that there must be either diffusion of ions from the tissue, or 

 that one of the ions of water must enter along with the excess 

 of salt ion absorbed. Resulting from this, the solution must 

 become acid or alkaline. Pantanelli himself inclines to the 

 latter view. D. R. Hoagland, however (Science, 48, 422-5, 

 1918), questions the evidence upon which the opinion rests that 

 water culture solutions become markedly acid or alkaline 

 owing to excess absorption of one ion of a salt. On the con- 

 trary, he found that when plants were put into nutrient solu- 

 tions with an acid reaction, this last became neutral after the 

 solutions had remained in contact with the roots for some 

 time. Similarly, when plants were transferred to solutions of 



