272 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



the backward ejection of water, whereas Schultze, Pfitzer, and Engelmann * 

 concluded that it was the result of the movement of extracellular masses of 

 protoplasm, which by friction against the surrounding media produced 

 a forward movement in the opposite direction. The existence and mode of 

 action of the extracellular protoplasm was, however, first determined by 

 O. Miiller 2 , who showed that the protoplasm exudes through the polar 

 furrow on each of the valve sides, streams along the crevice of the raphe to 

 its termination at the median nodule, where each stream returns to the 

 interior, and travels back internally. Although most Diatoms usually lie 

 on one of the valve sides, some forms frequently lie on the girdle side 

 where the edges of the valves overlap, but even here sufficient energy is 

 developed to move the Diatoms along by the friction of the protoplasm 

 against the surrounding water 3 . It is, however, only on the valve sides that 

 any movement of adhering particles by the streaming protoplasm can be 

 seen, and Schultze has shown that they are only moved as far as the end of 

 the valve and not around its edge 4 . 



The extracellular protoplasmic layer is extremely thin, but this does not 

 affect its frictional surface, and Miiller 5 has shown that the rate of streaming 

 need not exceed 3 mm. per minute to produce a velocity of movement 

 of about i mm. per minute, which is approximately the maximal speed 

 shown by any Diatom. These values correspond very well with the 

 rates of streaming shown in large plant-cells, and Ewart has shown that 

 whereas the streaming protoplasm of a Diatom may perform 0-5 to 0-8 erg 

 of work per minute per gram of moving plasma, the streaming protoplasm 

 of large plant-cells only performs 0-18 to o-32 erg per minute per gram of 

 streaming protoplasm 6 . 



Although Diatoms may adhere to a surface-tension film and creep 

 along it, the exceptional cases of free-swimming observed by Pfitzer have 

 been denied existence by Miiller 7 . It is, however, impossible to doubt that 

 a slowly-sinking Diatom would show lateral progression if its long axis 

 was more or less horizontal, and if the protoplasm was streaming in the 

 usual manner along the raphe. Under such circumstances a tendency 



Schultze, Archiv f. mikr. Anat. 1865, p. 388; Pfitzer, Unters. iiber Bau u. Entwickelung d. 

 Diatomeen, 1871, p. 176 (in Hanstein's Bot. Abhandl., Bd. i) ; Engelmann, Bot. Ztg., 1879, p. 54. 



3 O. Miiller, Ber. d. hot. Ges., 1899, p. 445; 1897, p. 70; 1889, p. 169. Summaries are given 

 by Karsten, Die Diatomeen d. Kieler Bucht, 1899, P- ^3 I Klebhahn, Archiv f. Protistenkunde, 

 i(jO2, Bd. i, p. 429. Lauterborn (Unters. iiber Diatomeen, 1896, p. 113) has recently adopted 

 Muller's views. 



3 O. Miiller, Ber. d. bot. Ges., 1894, p. 143 ; Karsten, I.e., p. 165 ; Benecke, Jahrb. f. wiss. Bot., 

 1900, Bd. xxxv, p. 551. 



* O. Miiller, 1. c., 1894, p. 143 ; M. Schultze, 1. c. 



5 O. Miiller, I.e., 1897, p. 75. Miiller (I.e., 1896, p. 121) observed velocities of 0-007 to 

 0-017 mm. per second. The colourless forms move most rapidly, according to Benecke (1. c.). 



6 Ewart, Protoplasmic Streaming in Plants, 1903, p. 31. 



7 Pfitzer, I.e., p. 176. Cf. O. Miiller, Ber. d. bot. Ges., 1896, p. 128. 



