424 C. M. CHILD. 



the metabolic rate existing before the action of the external agent 

 and it is not yet certain that such a change occurs in this case. 

 Certain reversals of the gradient in Griffithsia described below 

 (p. 430) where true acclimation is out of the question, show that 

 reversal does not necessarily mean acclimation. 



In Enteromorpha also, where the susceptibility gradient to 

 high concentrations is like that of Cladophora, basipetal (Child, 

 'i6a) a reversal of the gradient often appears in neutral red, and 

 in various other species more or less reversal has frequently been 

 observed in neutral red. These and other cases of reversal are 

 discussed in a later section (p. 436). 



One series of observations made on portions of a single plant 

 of Cladophora gave results very different from those recorded 

 above as regards neutral red. Portions of this plant stained 

 with neutral red showed no decoloration even after a week or ten 

 days, although to judge from the contracted and disintegrated 

 appearance of the protoplasm death had undoubtedly occurred. 

 Other portions stained and then killed in alcohol 10 per cent, and 

 5 per cent, and in ethyl ether 4 per cent, likewise showed no 

 decoloration during three or four days, as long as the preparations 

 were kept, although the altered appearance of the protoplasm 

 even after a few hours gave every indication that death had 

 occurred. In these cases the apical regions for a length of 

 several cells were stained an opaque black, and other portions 

 were deep purple, the color indicating a much higher acidity 

 within the cells than that usually observed. Portions of the 

 same plant in KCN m/^o after staining with neutral red showed 

 the usual basipetal decoloration gradient and were completely 

 decolorized after twenty-four hours like other specimens ex- 

 amined. 



This case occurred at the end of my stay at Woods Hole so 

 that there was no opportunity for further tests and it is men- 

 tioned here only because of the possibility that others, attempting 

 to repeat my experiments, might obtain such results as these. 

 The same behavior as regards neutral red was observed once 

 before in a single test of a fresh water species of Cladophora. 

 In neutral red no decoloration occurred even after two weeks, 

 although the plant was undoubtedly dead. Further investiga- 



