258 Pub. Puget Sound Biol. Sta. Vol. 2, No. 48 



Odonthalia shows somewhat different conditions. Here, as in the 

 other forms, methylene blue enters readily and a distinct staining gradient 

 appears, but on return to water the cells do not give up the dye. Moreover, 

 for this form methylene blue is dictinctly toxic and kills when it reaches a 

 sufficient concentration in the cells, and when the cells die the dye comes 

 cut, together with the plant pigment, leaving the dead cells green. The 

 death gradient is basipetal like the susceptibility gradients to other agents, 

 but the differences in time of death along the axis are very much greater 

 than the differences in rate of staining. 



The work with methylene blue was not begun until late in the season 

 of 1918 and was done chiefly with the three forms mentioned. These few 

 observations are, however, sufficient to show that the cells of diflferent 

 species, although all highly permeable to methylene blue, differ widely in 

 their relation to it. Its toxicity apparently depends, not on the permeability 

 of the mebrane to it, but upon the degree to which it reacts physically or 

 chemically with some constituent or constituents of the cell. With methy- 

 lene blue, as with neutral red, the staining gradient, i. e., the gradient in 

 permeability, may play some small part in determining the death gradient, 

 but it seems clear that other conditions within the protoplasm rather than 

 the permeability of its limiting surfaces are the chief factors in determining 

 the course and rate of progress of death along the axis. When, for example, 

 all parts of an elongated cell stain uniformly so far as can be seen, as is 

 usually the case in these two dyes, but the death changes begin at the apical 

 end of the cell and progress in an orderly way, reaching the basal end only 

 after several minutes, it seems obvious that other factors than permeability 

 arc chiefly concerned in determining the course and rate of progress of 

 death. 



The results with these vital dyes enable us to distinguish to some extent 

 between susceptibility and permeability. The permeability gradient and 

 the susceptibility gradient show similar axial relations, but the permeability 

 gradient is much less strongly marked. The logical conclusion from these 

 facts is that differences in permeability are associated with other differences 

 in physiological condition in the cells, but that the permeability varies much 

 less widely than the conditions on which susceptibility depends. 



Observations were made on a few species with KMnOj^. In all cases 

 the staining gradient resulting from the reduction of the permanganate 

 corresponded to the susceptibility gradient observed with other agents. In 

 monosiphonous forms with more or less transparent cells, e. g., Calli- 

 thamnion, not only the change in color, but the changes in aggregation of 

 protoplasm can be followed within the single cell and, as with other agents 

 a basipetal intracellular gradient in these changes appears. Moreover, the 



