CHAPTER IV 



LOCOMOTORY AND PROTOPLASMIC MOVEMENTS 



PART I 



THE CHARACTER AND MECHANISM OF MOVEMENT 



SECTION 57. General. 



APART from the spermatozoids of vascular cryptogams and a few 

 Gymnosperms, no power of independent locomotion is shown by any 

 vascular plant. Many Fungi, and an even larger number of Algae, produce 

 motile zoospores, and in the case of many Volvocineae, Flagellatae, Bacteria, 

 Diatomaceae, and Myxomycetes the power of active locomotion is only 

 interrupted by certain resting stages, or during reproduction. 



Motile organisms are usually free-swimming and possess special loco- 

 motory organs such as cilia or flagellae ; but others creep or glide over the 

 substratum, and others again show amoeboid movements over moist surfaces 

 or even under water. No plant or part of a plant is, however, able to propel 

 itself through the air, although spores and winged seeds may float in it 

 for some time. The different types of movement are not always sharply 

 distinguished, and the zoospores of Myxomycetes may perform alter- 

 nately amoeboid and ciliary locomotion. Indeed, transitions occur between 

 transitory pseudopodia and typical cilia, while certain Infusoria may either 

 swim freely or run over the substratum by the aid of their cilia. A swimming 

 movement will always become a gliding one when an organism is fixed 

 to the substratum by a mucilaginous layer, which is viscous enough to 

 prevent the upward escape of the organism but not its lateral movement. 



Transitions also occur between the active movements of rooted plants 

 and of free-swimming organisms. Thus a swarm-spore attached at one end 

 performs nodding and bending movements like a rooted plant. In addition, 

 the movement of certain Desmids due to the excretion of a gelatinous stalk 

 may be compared with the movement of a growing apex produced by the 

 elongation of the zones beneath. Growth curvatures cause locomotory 

 movements in the free threads of Spirogyra, and may also cause them to 

 group together in bunches. 



Dermatoplasts may remain capable of swimming and gliding move- 

 ments, whereas the production of a rigid cell-wall renders external amoeboid 

 movement impossible so long as no extra-cellular protoplasm is present. 



