GLIDING MOVEMENTS 275 



a Desmid, it would be extremely difficult, even under the highest powers of 

 the microscope, to detect its mode of progression by moving the ventral 

 scales attached to the ribs. 



SECTION 60. Amoeboid Movement. 



Pronounced amoeboid movements are only shown among plants by 

 the plasmodia and swarm-spores of Myxomycetes, as well as by the 

 zoospores of a few Fungi, and the zoospores and tetraspores of a limited 

 number of Algae l . All other gymnoplasts (zoospores, ova, &c.) and also 

 plasmolysed protoplasts show no power of amoeboid movement, although 

 slow internal amoeboid movements may be possible, and do often in fact 

 cause alterations in the shape of the vacuoles. In addition, the reproductive 

 nuclei of the pollen-tubes of Phanerogams appear to be capable of slow 

 amoeboid change of shape. The same applies to the nuclei in the epidermal 

 hairs of Tradescantia and in the leaf-cells of Elodea canadensis, and the 

 movement appears to become more active under the action of asparagin 2 . 



The protrusion of the pseudopodia is often followed by retraction, but 

 progression is possible in a definite direction when a pseudopodium steadily 

 enlarges until the whole body has flowed into it 3 . The pseudopodia of 

 Rhizopoda are extremely fine and slender, whereas Myxomycetes, in 

 addition to forming short fine pseudopodia, also produce broader-lobed, 

 fan-like or netted expansions. In plasmodia the amoeboid activity appears 

 to undergo an autonomic alternation from one side to the other, which 

 causes a to-and-fro streaming of the fluid contents. The latter is always 

 directed towards the developing pseudopodia, but it is not shown in all 

 cases 4 , as for instance in the zoospores of Myxomycetes. These are also 

 provided with cilia, and when swimming freely often perform leaping or 

 backward movements when the cilia collide with a resistant body 5 . 



Amoeboid locomotion is a form of vital activity which is not ex- 

 plained by saying that it is due to the expansion and contraction of the 

 protoplasm. To speak of the rounding off under strong excitation as being 

 due to a spherogenic activity, and the re-expansion as being due to 



1 Berthold, Protoplasmamechanik, 1886, p. 94; de Bary, Morphologic u. Biologic d. Pilze, 

 1884, p. 174; Zopf, die Pilze, 1890, p. 102. On the amoeboid movements of Protozoa cf. Hertwig, 

 Die Zelle u. d. Gewebe, 1893, p. 55 ; Verworn, Allgemeine Physiologic, 1901, 3. Aufl., p. 244. 



* Kohl, Bot. Centralbl., 1897, Bd. LXXII, p. 168. Cf. also Mottier, Fecundation in Plants, 

 1904. Amoeboid movements are often shown by the nuclei of animals. 



s De Bary, Morphologic u. Biologic d. Pilze, 1884, p. 453; Zopf, in Schenk's Handb. d. 

 Botanik, 1887, Bd. in, 2. Halfte, p. i ; Pfeffer, Zur Kenntniss d. Plasmahaut u. d. Vacuolen, 1890, 

 p. 256. On Amoeba and other animals cf. Khumbler, Archiv f. Entwicklungsmechanik, 1898, 

 Bd. viu, p. 114; Jensen, Die Protoplasmabewegung, 1902, Sep. a. Ergebnisse der Physiol., I. Jahrg. 



* Cf. Berthold, 1. c., p. 109 ; Jensen, 1902, 1. c., p. 14. 



s De Bary, I.e., p. 954; Fayod, Pot Zt., 1883, p. 171. 



T 2 



