96 INJURY, RECOVERY, AND DEATH 



of carbon dioxide by Laminaria steadily decreased. If 

 the tissue was replaced in sea water after exposure to 

 NaCl the recovery (as judged by the rate of production 

 of CO 2 ) was either partial or complete according to the 

 degree of depression which the rate had undergone. The 

 results are shown in Fig. 39. It will be seen that they 



20*- 



HOURS 2 



FIG. 39. Curves showing rate of respiration of Laminaria agardhii (expressed as per cent, 

 of the normal). The normal rate represents a change from pH 7.78 to 7.36 in from 1^4 to 2 

 minutes, depending upon the amount of material used. The solid lines show rate of res- 

 piration during one hour of exposure to isotonic sodium chloride (0.52 M for Woods Hole sea 

 water). The dotted lines show stages of recovery after the tissue was put back in normal 

 sea water. Each curve represents a typical experiment. 



offer a striking parallel to those obtained by measuring 

 the electrical resistance. 



Similar results are observed where we employ hyper- 

 tonic or hypotonic solutions in place of NaCl. When 

 Laminaria is placed in dilute sea water, or in sea water 

 concentrated by evaporation, injury may occur, and recov- 

 ery may be partial or complete. This is true whether we 

 use electrical resistance or rate of production of C0 2 as 

 the criterion of injury and recovery. The results obtained 

 by Inman (1921, A) with hypertonic solutions are shown 

 in Fig. 40. 



The fact that in the case of Laminaria and Chlorella 

 recovery may be either partial or complete, according to 

 circumstances, raises the question whether this is also 

 true of other forms. It is certainly true of all the plants 



