SOME OBSERVATIONS ON DIATOM MOTION. 



BY T. CHALKLEY PALMER. 



Ill a recent contribution to these Proceedings the opinion 

 was expressed that certain theorists, in their endeavor to 

 evolve a non-protoplasmic explanation of diatom motion, 

 had unduly emphasized both the attractive force excited by 

 light upon the moving diatom, and the chlorophyll reaction as 

 a motive force. A recent writer* was quoted to the effect 

 that motion does not take place in diatoms unless the light is 

 " fairly strong." The osmotic theoiy, indeed, based as it is 

 on the action of light upon the endochrome of the diatom cell, 

 needs above everything that this be so. But the statement is 

 not based upon facts cited, nor warranted by any known to 

 the present writer. 



That diatoms may move in almost complete absence of 

 light is highly probable. That they do move, and with vigor, 

 under conditions that forbid any but the most feeble sort of 

 photosynthesis, appears demonstrable. In April, of the pre- 

 sent year, experiments as to the effect of one kind of light 

 were made upon motile diatoms in a fresh, healthy gathering 

 abounding in naviculoid forms. The conditions were as 

 follows : 



A Continental microscope stand, with large, square stage, 

 was adjusted with a two-thirds objective, an achromatic con- 

 denser oi ioo° aperture, and such tube length and eyepiece 

 amplification as to make the apparent field fourteen centime- 

 ters ill diameter. The stage having been inclined at such an 

 angle that no direct rays from the lamp should fall upon it, 

 the condenser was screwed up until the image of the flame 

 sharply focussed upon the centre of the field. The iris dia- 

 phragm was then closed until the image was sharp but mild, 

 all irradiation having been cut off. The source of light in all 

 the experiments was a Welsbacli mantle. In the first series 

 ( Figures 1 to III ) the image of the whole mantle was used. 



'■■■"]VIr. I). 1). Jiic'kson, "American Naturalist," May, 1905. 



