VI] MACALLUM'S EXPERIMENTS 291 



accordingly, a concomitant of the diminished surface tension which 

 is manifested in the altered configuration of the system. 



In the case of ciliate or flagellate cells, there is to be found a 

 characteristic accumulation of potassium at and near the base of 

 the cilia. The relation of ciliary movement to surface tension 

 hes beyond our range, but the fact which we have just mentioned 

 throws hght upon the frequent or general presence of a little 

 protuberance of the cell-surface just where a flagellum is given 

 of£ (cf. p. 247), and of a little projecting ridge or fillet at the base 

 of an isolated row of cilia, such as we find in Vorticella. 



Yet another of Professor Macallum's demonstrations, though 

 its interest is mainly physiological, will help us somewhat further 

 to comprehend what is implied in our phenomenon. In a normal 

 cell of Spirogyra, a concentration of potassium is revealed along 

 the whole surface of the spiral coil of chlorophyll-bearing, or 

 " chromatophoral," protoplasm, the rest of the cell being wholly 

 destitute of the former substance : the indication being that, at 

 this particular boundary, between chromatophore and cell-sap, 

 the surface tension is small in comparison with any other interfacial 

 surface within the system. 



Now as Macallum points out, the presence of potassium is 

 known to be a factor, in connection with the chlorophyll-bearing 

 protoplasm, in the synthetic production of starch from COg under 

 the influence of sunlight. But we are left in some doubt as to 

 the consecutive order of the phenomena. For the lowered surface 

 tension, indicated by the presence of the potassium, may be 

 itself a cause of the carbohydrate synthesis ; while on the other 

 hand, this synthesis may be attended by the production of sub- 

 stances (e.g. formaldehyde) which lower the surface tension, and 

 so conduce to the concentration of potassium. All we know for 

 certain is that the several phenomena are associated with one 

 another, as apparently inseparable parts or ine\'itable concomitants 

 of a certain complex action. 



And now to return, for a moment, to the question of cell-form. 

 When we assert that the form of a cell (in the absence of mechanical 

 pressure) is essentially dependent on surface tension, and even when 

 we make the preliminary assumption that protoplasm is essentially 



19—2 



