274 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



to be present, although certain observers appear to have mistaken adhering 

 flagellate bacteria for them. 



Although foreign particles adhering to or embedded in the mucilaginous 

 sheath may be moved along spiral lines around the filament, this is not 

 shown over the whole length of the filament, and according to Correns 

 a portion of the filament always adheres to the substratum during loco- 

 motion. The latter never exceeds 0-004 of a mm. per second, a velocity 

 which does not suffice for free-swimming movement. Nageli 1 and Kolk- 

 witz - state, however, that free-swimming is shown on rare occasions, and 

 Kolkwitz also observed a creeping locomotion on the surface of the 

 water. 



The radiating arrangement of Oscillaria colonies when growing on 

 moist substrata 3 probably results from the realized movements along the 

 path of least resistance. Similar groupings may be shown by the threads 

 of Spirogyra and by Diatoms 4 . Hansgirg concludes that stimulatory 

 reactions also come into play, but without bringing forward any definite 

 proof 5 . 



Desmidiaceae. The slow movements of Desmids are due, according to 

 Klebs, to the excretion of mucilage, and it is in fact easy to see that 

 certain forms are actually raised to a certain height in water by the 

 formation of a gelatinous stalk 6 . Progression would also be possible over 

 a substratum by the continued forcible excretion of mucilage from the 

 hinder end. Many Desmids progress with one end only resting on the 

 substratum, the body being inclined obliquely upwards, while the attached 

 end may change from time to time. This applies to Closterium inoniliferum, 

 which shows a phototactic progression to light by turning repeatedly over 

 so that first one end and then the other is attached to the substratum as it 

 moves towards the light 7 . 



It does, however, seem probable that the locomotion is due to the 

 regulation of the excretion of mucilage, although it does not follow that 

 the same means of locomotion is used in all cases, and in fact many 

 Diatoms and a few Desmids adhere very firmly to stones and rocks. In 

 any case it is worthy of note that if a snake were reduced to the size of 



1 Nageli, Beitrage z. wiss. Bot., 1860, Heft ii, p. 90. 3 L. c., p. 466. 



3 Nageli, 1. c., p. 91. 



* Schultze, Archiv f. mikr. Anat., 1865, Bd. I, p. 396. 



5 Hansgirg, 1. c., 1893, p. 207. 



6 Klebs, Biol. Centralbl., 1885, Bd. V, p. 353 ; Unters. a. d. hot. Inst. zu Tubingen, 1886, Bd. II, 

 P- 383; Stahl, Bot. Zeit., iSSo, p. 397; Verhandl. d. phys.-med. Ges. in Wiirzburg, 1879, Bd. XIV; 

 Aderhold, Jenaische Zeitschrift f. Natnrw., iSSS, N. F., Bd. XV, p. 323. On the excretion of 

 mucilage by Desmids cf. Schiitt, Jahrb. f. wiss. Bot., 1^99, Bd. XXXIII, p. 676 ; Schroder, Verhandl. 

 d. naturh.-med. Vereins in Heidelberg, 1902, N. F., Bd. vn, p. 139; Lutkemiiller, Cohn's Beitrage 

 z. Biol., 1902, Bd. vin, p. 347. 



7 Stahl, I.e. 



