328 BOTANY PART I 



development. We thus confine ourselves to the protoplasmic move- 

 ments among which the AMOEBOID MOVEMENT, the CILIARY MOVE- 

 MENT, and the MOVEMENT OF PROTOPLASM IN CELLS WITH CELL WALLS 

 may be distinguished. 



The creeping movements of naked protoplasts, such as are shown 

 by an amoeba or plasmodium, in the protrusion, from one or more 

 sides, of protuberances which ultimately draw after them the whole 

 protoplasmic body, or are themselves again drawn in, are distinguished 

 as AMOEBOID MOVEMENTS. These movements resemble, externally, the 

 motion of a drop of some viscous fluid on a surface to which it does 

 not adhere, and are chiefly due to surface tension, which the proto- 

 plasm can at different points increase or diminish by means of its 

 quality of irritability. 



By means of local changes of surface-tension similar amoeboid movements 

 are also exhibited by drops of lifeless fluids, such as drops of oil in soap solution, 

 drops of an oily emulsion in water, or drops of mercury in 20 per cent solution of 

 potassium nitrate in contact with crystals of potassium bichromate. 



In the SWIMMING MOVEMENTS BY MEANS or CILIA ( 89 ), on the con- 

 trary, the whole protoplasmic body is not involved, but it possesses 

 special organs of motion in the form of whip-like FLAGELLA or CILIA. 

 These may be one, two, four, or more in number, and arranged in 

 various ways (Figs. 216, 219). They extend through the cell wall when 

 this is present and move very rapidly in the water, imparting con- 

 siderable velocity to the protoplast, often giving it at the same time 

 a rotary movement. The minute swarm-spores of Fuligo varians tra- 

 verse 1 mm. (sixty times their own length) in a second, those of Ulva 

 0'15 mm., while others move more slowly. The Vibrio of Cholera, 

 one of the most rapidly moving bacteria, takes 22 seconds to traverse 

 a millimetre. 



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

 which have a slit or raphe in the siliceous cell wall glide along, usually in a line 

 with their longitudinal axis, and change the direction of their movements by 

 oscillatory motions. From the manner in which small particles in their neigh- 

 bourhood are set in motion, it is concluded that there exists a current of proto- 

 plasm, which bursts through the raphe ; this, according to 0. MULLEK, is the 

 cause of the movement ( 90 ). The cells of Desmidiaceae effect their peculiar 

 movements by local fluctuations in the mucilaginous excretion. The Oscillarieae 

 appear to behave similarly ( 91 ). 



In addition to such changes of place of whole cells there are also 

 movements of the protoplasm within the cell wall. Of these move- 

 ments rotation and circulation (cf. p. 1 3) have to be distinguished. 



In these movements the outermost layer of protoplasm in contact witli the cell 

 wall remains at rest ; the movement cannot thus be compared to that of an 

 amoeba enclosed in a cell. The movement continues when the protoplasm has 

 been detached from the cell wall. Its cause must be looked for in surface 

 tensions between the protoplasm and the cell sap. 



