VI] OF MACALLUM'S EXPERIMENTS 461 



from the physiological point of view, we call the phenomenon 

 the first stage in the process of conjugation. In the figure of 

 Mesocarpus (a close ally of Spirogyra), we see the same phenomenon 

 admirably exemplified in a later stage. From the adjacent cells 

 distinct outgrowths are being emitted, where the surface-tension has 

 been weakened: just as the glass-blower warms and softens a small 

 part of his tube to blow out the softened area into a bubble or' 

 diverticulum; and in our Mesocarpus cells (besides a certain 

 amount of potassium rendered visible over the boundary which 

 separates the green protoplasm from the cell-sap), there is a very 

 large accumulation precisely at the point where the tension of the 

 originally cylindrical cell is weakening to produce the bulge. 

 But in a still later stage, when the boundary between the two 

 conjugating cells is lost and the cytoplasm of the two cells becomes 

 fused together, then the signs of potassium concentration quickly 

 disappear, the salt becoming generally diffused through the now 

 symmetrical and spherical "zygospore." 



In a spore of Equisetum, while it is still a single cell, no 

 localised concentration of potassium is to be discerned; but as 

 soon as the spore has divided by an internal partition into two 

 cells, the potassium salt is found to be concentrated in the smaller 

 one, and especially towards its outer wall which is marked by a 

 pronounced convexity. As this convexity (which corresponds 

 to one pole of the now asymmetrical, or quasi-ellipsoidal spore) 

 grows out into the root-hair, the potassium salt accompanies its 

 growth and is concentrated under its wall. The concentration is, 

 accordingly, a concomitant of the diminished surface-tension which 

 is manifested in the altered configuration of the system. 



The Acinete protozoa obtain their food through suctorial tentacles 

 extruded from the surface of the cell : their extrusion being doubtless 

 due to a local diminution of surface-tension. A dense concentration 

 of potassium reveals itself, accordingly, in the surface-film of each 

 tiny tentacle. As the tentacles are withdrawn their potassium 

 diffuses into the cytoplasm; when retraction is complete it is again 

 found in surface-concentration, but the surface-films on which it 

 now concentrates are the surfaces of the protein-spherules (or "food- 

 vacuoles") within the body of the cell. 



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



