244 BOTANY 



Diatoms and Desmids exhibit quite a different class of movements. The 

 Diatoms glide along, usually in a line with their longitudinal axes, and change 

 the direction of their movements by oscillatory motions. From the manner in 

 which small particles in their neighbourhood are set in motion, it was concluded 

 that special organs of motion probably protrude, like pseudopodia, through openings 

 in their hard silicified shell ; while more recently, in a few instances, Hauptfleisch 

 has been able to render visible the protoplasmic motile organs. The protrusion of a 

 transparent thread of mucilaginous matter is claimed to have been seen by Butschli 

 and Lautbeeorn in the case of a large Diatom which propelled itself by this means. 

 This means of locomotion resembles that of the nearly related Desmids, which, it 

 has been shown, maintain their peculiar movements with the help of a similar 

 mucilaginous protrusion. The pendulous advancing movements of the filamentous 

 Oscillariae and Spirulinae are also said to be dependent upon similar mucilaginous 

 exudations. The mechanism of the movements of Spirogyra is still unexplained. 



The Movements of Protoplasm within Walled Cells 



Although plants which are firmly attached and stationary exhibit 

 no such locomotory movements, the protoplasm within their cells does 

 possess a power of movement. Such internal protoplasmic movements 

 are especially active in the non- cellular Siphoneae, in the elongated 

 internodal cells of the Characeae (Fig. 167), and often in the hairs of 

 many plants, as well as in the leaf-cells of some aquatic plants. The 

 active protoplasmic currents in Gaulerpa move along its outer walls and 

 around the internal cellulose bands, stretching from wall to wall in the 

 manner of an immense imprisoned plasmodium. 



The three following different forms of protoplasmic movement 

 within cell cavities may be distinguished : circulation, rotation, 



and ORIENTATION. 



In the case of circulatory movement the different currents of 

 protoplasm, although often quite close together, flow in different 

 directions. This motion is seen most frequently in cells of which the 

 nucleus is suspended in the centre of the cell cavity by means of 

 protoplasmic threads. In these threads continuous protoplasmic 

 currents flowing towards and away from the nucleus connect the 

 protoplasm enveloping it with the protoplasm clothing the cell wall 

 (Fig. 53). Sometimes, even in extremely fine threads of protoplasm, 

 two currents may be seen to pass each other (e.g. in the stamens of 

 Tradescantia, the stinging hairs of Urtica, and the bristles of Cuewbita). 



In the rotatory movement the protoplasm moves along the 

 cell wall in one direction only, dragging with it the nucleus and often 

 also the chlorophyll grains. In an elongated cell, in which the rotation 

 usually takes place in the direction of the longitudinal axis, as the 

 protoplasm forms one united body, there must be a strip of immovable 

 protoplasm which separates the rotating masses. This stationary 

 part is termed the neutral or interference zone. The rapidity 

 of the movement diminishes towards the cell wall, and the layer of 



