554 



NOTES. 



The Movements of Diatoms and other Microscopic Plants.* 

 By Daniel D. Jackson. 



Few subjects in the domain of Cryptogamic Botany have given rise- 

 to more speculation and conflicting theories than have the studies 

 into the cause of the apparently voluntary movements of diatoms. 

 From time to time for the past twelve years the author has been 

 confronted with this seemingly fruitless subject, and only recently, 

 almost by accident, has the problem been solved. 



It was early shown by examination in closed cells that the 

 phenomenon was not due to external currents set up in the sur- 

 rounding liquid, but that the power of motion came from the 

 organism itself. Largely on account of these movements, which 

 appeared to be spontaneous and voluntary, the diatoms were- 

 originally classed in the animal kingdom. 



The first theory which naturally presented itself was that they 

 move, as do the infusoria, by means of vibrating hair- like processes 

 called cilia or flagella. Later, certain authors claimed to have seen 

 protoplasmic processes similar to those of the rhizopods protruding 

 from the small openings in the frustule of the organism. Then 

 came the theory of Onderdonk,f which described the progression as 

 due to a thin fluid mass in rhythmical motion covering the surface 

 of the diatom. 



Nageli suggested that the motion is due to endosmotic and 

 exosmotic currents, and H. L. Smith.J after much study of the 

 subject, came to the conclusion " that the motion of the Navicular 

 is due to injection and expulsion of water, and that these currents 

 are caused by different tensions of the internal membranous sac in 

 the two halves of the frustules." 



In order to prove this theory, Professor Smith showed, by 

 means of suspended indigo, that when the diatom moves forward 

 the particles of indigo gather around the central nodule of the 

 valve and form a small mass, which turns on itself just as if it 

 were impelled by a jet of water proceeding from the valve at this 

 point. Each of these little turbulent spheres, after having acquired 



* ThiB paper, read at the May Meeting of the Society, had been previously 

 communicated to the New York Microscopical Society on April 7, 1905. 



t " The Movements of Diatoms," Microscope, August 1890. 



X "A Contribution to the Life History of the Diatomaceae," Proc. Amer. Soc, 

 Microscopists, 1888. 



