MOVEMENT OF CHLAMYDOMONAS 183 



to those of the arms in swimming. The action is of essentially 

 the same type wherever cilia are the organs of traction. The 

 rate of travel of these organisms is very slow as measured by 

 inches, but is rapid relative to their size. Thus, a Chlamydo- 

 monas occupies a mere fraction of a second in traversing a distance 

 equal to its own length, whilst in the case of a liner this evolution 

 requires several seconds. 



The direction of movement is influenced by various external 

 stimuli, such as light, distribution of chemical substances, etc. 

 If some water containing Chlamydomonas be placed in a glass 

 bottle covered, except for a small aperture on one side, with 

 brown paper, after exposure to illumination for some hours, 

 the organisms will be found to concentrate in a dense cluster 

 at the spot where the beam of light penetrates. If, however, 

 the latter is very intense, the plants swim away from the illumi- 

 nated region, which consequently becomes colourless. The 

 influence of the direction and intensity of the light on such 

 movements is spoken of as phototoxis. Just as in the case 

 of the movements of the protoplasts within the cells of higher 

 plants (cf. p. 4), the movement of these unicellular organisms 

 can be temporarily arrested by slight traces of anaesthetics. 



The Chlamydomonas-mdividual, with the help of its chloro- 

 plast, is able to manufacture food from simple inorganic sub- 

 stances like any other green plant, and as a result the cell 

 grows. After attaining a certain size it comes to rest, draws 

 in its cilia, and begins to form daughter-individuals (Fig. 96, f-i) . 

 The protoplast contracts slightly away from the wall and, after 

 nuclear division has taken place, gradually constricts into 

 two equal portions (/), each containing half the nucleus, chloro- 

 plast, etc. The resulting segments may divide again (g-h), and 

 these even for a third time (i), the successive divisions taking 

 place in planes at right-angles to one another. Each segment 

 develops a cell-wall and two cilia, and thus 2, 4, or 8 new 

 individuals are constituted which, apart from size, resemble the 

 parent in every respect. 



This process of vegetative reproduction is completed by the 

 rupture or dissolution of the membrane of the parent-cell, 

 with consequent liberation of the daughter-individuals. Since, 

 under favourable circumstances, the succession of events just 



