462 A NOTE ON ADSORPTION [ch. 



characteristic accumulation of potassium at and near the base of 

 the ciUa. The relation of ciliary movement to surface-tension* 

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

 throws light upon the frequent or general presence of a little 

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

 (cf. p. 406), 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 impHed 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 "chromato- 

 phoral," protoplasm, the rest of the cell being wholly destitute of 

 that substance : the inference 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. 

 And again, in certain minute Chytridia-like fungi, parasitic on 

 Spirogyra and the like, the potassium-reaction helps to trace the 

 delicate haustoria of the parasite in their course within the host-cell 

 — a clear indication of low surface-tension at the surface between. 



Now as Macallum points out, the presence of potassium is known 

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

 plasm, 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 substances 

 (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 ap- 

 parently inseparable parts or inevitable concomitants of a certain 

 complex aqtionf. 



* Cf. J. Gray, The mechanism of ciliary movement, Proc. U.S. (B), 1922-24. 



t The distribution of potassium within plant-cells is more complicated than it 

 seemed at first to be; but it is still the general if not the invariable rule to find it 

 associated (by adsorption) with one boundary-surface or another. Cf. E. S. 

 Dowding, Regional and seasonal distribution of potassium in plant tissues, Ann. 

 Bot. xxxix, pp. 459-470, 1925. The whole ciuestion, first adumbrated by Macallum, 



