PHYSIOLOGY 267 



current of protoplasm, which bursts through the raphe ; this may become invested 

 with a mucilaginous sheath. Corresponding to the differences in the construction 

 of the membrane, differences in the motile apparatus are found in the group. The 

 cells of Desmidiaceae attach themselves to the substratum by mucilaginous 

 excretions, and effect their peculiar movements by local fluctuations in the 

 mucilaginous layer. The advancing movements of the filamentous Oscillarieae 

 and Spirulinae take place, according to CORUENS, in a mucilaginous sheath, but 

 their mechanism is as little understood as that of the slow movements of 

 Spirogyra. 



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, and in 

 non-septate Fungi in the elongated internodal cells of the Characeae, 

 in the hairs of many plants, as well as in the leaf-cells of some 

 aquatic plants. 



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 in slender protoplasmic strands, which stretch from the 

 cell wall to the nucleus (cf. p. 58 and Fig. 60). 



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 (cf. p. 58). 



The cause of these movements, which may take different directions in adjoining 

 cells, and may also continue after the protoplasm has been drawn away from the 

 cell walls by plasmolysis (p. 180), is not yet understood. It is, however, known 

 that the continuance and activity of such protoplasmic movements, the existence 

 of which was first observed by CORTI in 1772, and later rediscovered by 

 TIIKVIRANUS in 1807, are dependent on factors which, in general, support and 

 promote the vital activity ; while the presence of free oxygen and proper 

 conditions of temperature seem to be particularly favourable to them. That the 

 movements in Nitella continued, according to KUHNE'S observations, for days and 

 weeks in the absence of oxygen is explained, according to HITTER, by the power 

 the Characeae possess of becoming facultative anaerobes. Those Bacteria which 

 are obligate anaerobes lose their power of motion in the presence of oxygen. 

 From the study of sections in the cells of which currents had been induced in 

 the protoplasm, by the injuries sustained in their preparation and by other 

 abnormal conditions, grave errors have arisen concerning the existence of such 

 protoplasmic movements in cells, in which under normal conditions they cannot 

 be observed. The presence of protoplasmic currents in a cell may, in fact, 

 indicate either an energetic vital activity, or, on the other hand, be merely a 

 symptom of a pathological or, at least, of an, excited condition of the proto- 

 plasm ( 7B ). 



