Notes. 555- 



a certain size, falls apart, and the particles which compose it are 

 driven along the valves from front to back, and accumulate behind 

 the extremity of the frustule which, according to its progression, 

 would be considered the rear. The particles move as if they were 

 subjected to a current going from front to back, and reverse when 

 the motion is reversed. That these currents exist there can be no- 

 doubt, but that the motive power is not due to the expulsion of 

 water will shortly be demonstrated. 



The first intimation of the true nature of this motion was 

 suggested by the action of a lithia tablet in a glass of water. The 

 bubbles of carbonic acid gas given off set up the exact motions in 

 the tablet that have been so often described for the movements of 

 diatoms — " a sudden advance in a straight line, a little hesitation, 

 then other rectilinear movements, and, after a short pause, a return 

 upon nearly the same path by similar movements." 



Eepeated experiments with compressed pellets evolving gas 

 have shown that this is the usual motion produced by the evolution 

 of gas bubbles ; and when pellets were made of the same shape as 

 Naviculse, the movements of these diatoms were perfectly dupli- 

 cated. Boat-shaped pieces of aluminium, 2 mm. thick, were then 

 made, and on them were cut longitudinal grooves to resemble 

 those of the diatom. When placed in strong caustic soda solution, 

 the movements of the metal produced by the evolution of hydrogen 

 gas again duplicated those of the diatom in a remarkable manner. 

 The metal having the grooves had a greater power of motion than 

 that without the grooves. 



If we consider that the diatom contains chlorophyll bands which, 

 when exposed to a strong light, rapidly evolve oxygen, and if we 

 take into account the fact that the motion does not take place 

 unless the light is fairly strong, we have then a conception of the 

 nature of the movements of these organisms. Streams of oxygen 

 may be readily seen evolving from all parts of many of the larger 

 aquatic plants when submerged in water and exposed to strong 

 light ; but in the diatom, while the gas produced is large compared 

 with the size of the organism, the actual amount evolved is so 

 small that it is taken into solution almost immediately. That 

 such evolution takes place, however, is shown by Professor Smith's 

 experiments with indigo. If, now, we examine the artificial diatom 

 made of aluminium, and placed in strong caustic solution, we find 

 that the bubbles from all sides come together and rise in a line 

 corresponding to the median line or raphe of the organism, and 

 that if indigo is placed in the liquid it collects and rotates near 

 the central °nodule, just as described by Professor Smith to prove 

 his theory of the presence of water currents. 



It is, therefore, evident that the motion of diatoms is caused 

 by the impelling force of the bubbles of oxygen evolved, and that 

 the direction of the movement is due to the relatively larger 



