112 PROCEEDrNGS OF THE ACADEMY OF [1898. 



the nature of diatom movements held by the proponents of the "os- 

 motic hypothesis," especially as this is set forth quite recently by 

 W. M. Kozlowski. 2 



The stimulating action of light upon the motile activity of the 

 errant frustules of Eunotia is not to be doubted, and has been ob- 

 served a number of times; but, up to the present, notwithstanding 

 that I have paid some attention to the matter, the phenomena ob- 

 served are not such as are incapable of classification under the head 

 of oxygen stimulation. No fact whatever has clearly indicated any 

 special tendency to motion in the direction of greatest illumination, 

 and after observing, under various conditions, the movements of 

 thousands of these frustules, I have strong doubt as to the existence 

 of any such tendency in Eunotia. 



Characteristics of movements. — Students of diatom movements 

 have, almost without exception, confined themselves to Pinnularia 

 and other naviculoid forms wherein the phenomena are most strik- 

 ing. H. L. Smith, 3 and, more recently, O. Biitschli 4 and R. Lauter- 

 born, 5 have been in practical agreement as to the phenomena, and to 

 a certain extent they agree in the conclusion that motion is the re- 

 sult of an expulsion of a more or less fluid filament from the central 

 nodule. O. Miiller, 6 agreeing with the others as to the phenomena, 

 looks rather, for their explanation, to currents of protoplasm which 

 circulate along the raphe within the coleoderm, entering into and 

 departing from the inner cell by way of the central and terminal 

 nodules. Hauptfleisch 7 has studied forms of Amphiprora and Bre- 

 bissonia, and by staining methods has apparently demonstrated in 

 these the existence of a protoplasmic canal penetrating the raphe, 

 through the delicate walls of which protrude exceedingly fine threads 

 of protoplasm which act like similar organs in the rhizopods. 



3 Botanical Gazette, Vol. XXIV, p. 39. Kozlowski presents in an ingenious 

 manner considerations supposed to point to the conclusion that in Pimndaria 

 motion is due to unequal photosyntax in the two ends of the frustule, causing 

 stronger inward currents of assimilable liquid and gas in one or the other 

 end, this difference depending upon the unequal illumination of the two ends. 



3 Proceedings Amer. Hoc- Micros., 1836. 



4 Mittheilung iiber die Bewegung der Diatomeen, Heidelberg, 1892. 



5 Untersuchungen iiber Bau, Kerntheilung und Bewegung der Diatomeen, 

 Leipsic, 1896. 



6 Berichte der Deutsch. Botan. Gesellsch. : Bd. VII, pp. 169-180 : Bd. XI, 

 p. 571. 



7 Mittheilungen des naturwiss. Vereins fiir Neu-vorporamern und Riigen, 

 Jahrg., XXVII. 



