74 



BOTANY 



PART I 



fan shapes, and also filamentous ribbon- and chain-like forms. Rod-shaped and 

 spirally-wound forms are met with in the Bacteria (Fig. 80 a, c, d}. 



Such living beings may be attached by mucilage to a substratum or may float 

 free in water. The free-floating organisms of continental water surfaces as well as 

 of the ocean are termed PLANKTON in contrast to the firmly -attached aquatic 

 organisms which constitute the BENTHOS. The plankton flora, which is rich in 

 peculiar species, contains such forms as have been mentioned above. These may 

 have the power of active movement (swimming forms) due as a rule to projections 

 of the protoplast as slender contractile flagella or cilia which are special organs of 



locomotion. This power of movement enables 

 many organisms of the plankton, responding 

 to stimuli, to seek for favourable nutritive 

 conditions or to avoid unfavourable spots. 

 Other forms of the plankton are suspended 

 without true power of movement in the water 



FIG. 79. Pinnularia viridis. A, Surface 

 view. B, Lateral view, (x 540. 

 After STRASBURGER.) 



FIG. 80. Bacteria from deposits on teeth, a, 

 Leptothrix buccalis; a*, the same after treat- 

 ment with iodine ; b, Micrococcus ; c, Spiro- 

 chaete dentium after treatment with iodine ; 

 d, Spirillum sputigenum. (x 800. After 

 STRASBURGER.) 



(floating forms). Many of them, and other plankton organisms, show special 

 arrangements for flotation in the increase of body surface by long bristles, bars, 

 and plates. The friction of the body against the water is thus considerably 

 increased and sinking made more difficult ( 51 ). 



3. Establishment of Polarity. The next stage in progressive 

 complexity of form is the establishment of the distinction between 

 base and apex. In freely motile forms the cilia are frequently 

 attached at one pole. In fixed forms one pole forms an ORGAN OF 

 ATTACHMENT, as, for instance, a circular disc of attachment or 

 palmately-branched lobes. The further growth may at the same time 

 be restricted to a small region of the body or GROWING POINT. This 



