264 LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



Mechanical factors of this kind are of the greatest biological impor- 

 tance 1 , for they aid in the dispersal of seeds, pollen-grains, spores, and 

 bacteria by wind and water. The same applies to many freely motile 

 organisms, which are only able to cover comparatively small distances by 

 the aid of their own activity, since their absolute velocity of movement is 

 small. Within these limits, however, the organisms are able to seek 

 out the regions where the best conditions for their nutrition and develop- 

 ment prevail. 



SECTION 58. Ciliary Movement. 



Most motile vegetable organisms possess fine hair-like protoplasmic 

 projections, which are termed cilia when small and numerous, flagellae when 

 long and few in numbers, although naturally transition forms occur. In 

 some cases the cilia are uniformly distributed, but in others are grouped in 

 one or more bundles, while the flagellae are usually restricted to a definite 

 point on the body 2 . 



Many of the gametes and zoospores of Algae, as well as the cells of 

 Chlamydomonas, have two flagellae attached at the germinal spot, while the 

 zoospores of Oedogonium have a group of large flagellae arranged around 

 the anterior hyaline end 3 . In these radial objects the flagellae are placed at 

 the anterior end of the oval body, whereas in the dorsiventral Peridineae 

 and in the zoospores of Phaeophyceae they are laterally inserted. The 

 zoospores of Vaucheria have cilia over their whole surface 4 , and the same 

 applies to the coenobia of Pandorina and Volvox, although the individual 

 cells have each a pair of cilia only. In another member of the Volvocineae, 

 Gonium, the individual cells are arranged to form a flat plate-like expansion 

 covered with cilia on one side. 



Among Bacteria the cilia may either be distributed all over the body 

 or a tuft or a single cilium may be present at one or both ends. The latter 

 applies usually to Spirillum, which is spirally twisted like the sperms of 

 Ferns, although these have only the anterior end covered with a diffuse tuft 

 of cilia. The sperms of Mosses are rod-like in shape, and have only a pair 

 of cilia at the anterior end. 



A few of the zoospores mentioned have cilia of unequal size, and in 

 many Flagellatae and Peridineae one of the flagellae is pointed in the 



1 Cf. Ludwig, Biologic der Pflanzen, 1895. 



8 Cf. Hertwig, Die Zelle und die Gewebe, 1893, p. 64. 



3 See Hofmeister, Pflanzenzelle, 1867, p. 28 ; Falkenberg in Schenck's Handbuch d. Botanik, 

 1882, Bd. n, p. 194 (Algae); Zopf, Die Pilze, 1890, p. 61 seq. ; A. Fischer, Jahrb. f. wiss. Bot., 

 1895, Bd. xxvil, p. 84 (Bacteria) ; Migula, System d. Bacterien, 1897, Bd. I, p. 97 ; Ellis, Centralbl. 

 f. Bact., 2. Abth., 1902, Bd. IX, p. 546. On animal organisms and certain lower Algae cf. Biitschli, 

 Die Protozoen, 1880-9. On Flagellatae and Peridineae cf. also A. Fischer, Jahrb. f. wiss. Bot., 1894, 

 Bd. xxvi, p. 330; Schiitt, Die Peridineen d. Planktonexpedition, 1895, p. in. 



* Cf. Strasburger, Histologische Beitrage, 1900, Heft vi, p. 187. 



