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Walter Stiles 
stage of water loss as the membranes are rendered more permeable. 
The exact shape of the absorption-time curve in any particular case 
must depend on the concentration of the external solution, the 
permeability of the cell to the external solute and the rate at which 
the solute acts on the cell membranes in rendering them permeable 
to the solutes of the cell sap. Thus it is not to be expected that the 
behaviour of the tissue in regard to water gain or loss will be the 
same with different toxic substances, nor is this the case. 
4. Sulphuric acid, osmic acid and mercuric chloride 
These substances influence the swelling of potato rather similarly 
to those just discussed, that is, there is a preliminary period of 
Fig. 12. Curves illustrating the influence of sulphuric acid on the absorption 
of water by potato tuber. (After Stiles and Jprgensen.) 
swelling followed by a period of shrinkage. There is no doubt that 
acids are absorbed by plant tissue, the evidence for which will be 
discussed in a subsequent chapter. The results obtained for sulphuric 
acid are shown in Fig. 12. It will be observed that in a concentration 
of iV/5o ^e intake of water reaches a maximum in about an hour, 
while in a concentration as low as N /2000 the swelling gives place to 
shrinkage after 4 or 5 hours. Even in iV/5000 sulphuric acid shrinkage 
supervened before the lapse of 24 hours while in distilled water the 
tissue was still undergoing slow swelling after this lapse of time. 
