122 PALMER : 



motile diatoms. Nothing, it would seem, could be more con- 

 clusive as to the essential sameness of the nature of motion in 

 monads and diatoms, than the fact that l)oth monads and dia- 

 toms require oxygen in order to perform motion, that they 

 come to rest when oxygen becomes scarce, and that they 

 resume their motion when oxygen is again supplied. 



The predominant chemical process of diatom motile activ- 

 ity, then, is exothermic, and involves absorption of oxygen 

 and evolution of carbon dioxide. 



Since the above facts are by no means new, it is with a 

 feeling of pained surprise that one comes to read the recent 

 article of D. I). Jackson, on " Movements of Diatoms and 

 other Microscopic Plants."* This writer begins with point- 

 ing out the difficulty observers have experienced in arriving at 

 an understanding of the mechanism of motion in diatoms. 

 Several views are referred to, including that of Nageli, who 

 suggested that "the motion is due to endosmotic and exos- 

 motic currents" and that of H. L. Smith, who believed he 

 had demonstated " that the motion of the Naviculo' is due to 

 injection and expulsion of water." After stating that cur- 

 rents of some sort can be seen in operation along the valves 

 of diatoms, the author says : 



" 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." 



Mr. Jackson then describes these motions, and shows how 

 they can be duplicated by artificial diatoms of aluminium cut 

 to a naviculoid shape and immersed in a solution of strong 

 caustic soda. Bubbles of hydrogen were generated, and the 

 small pieces of aluminium repeated the movements of the dia- 



""■ American Naturalist. May, igo.S- 



