127 



which serves such plants for stem and leaves is called a thallus. 

 For our purposes the plants in this group may be sub-divided 

 as follows : 



1. Algae . Plants containing chlorophyll. 



3* ^T a ] olourleSS plants without chlorophyll. 



1 13. Algae. This group is of very 



little importance to the Forest Officer and contains plants of 

 simple structure which live, chiefly, in fresh or salt water, but 

 also on a damp substratum, such as moist soil, the bark of 

 trees in shady forests, etc. Many are coloured green ; others 

 are blue-green, brown, red or purple, in such cases some 

 other pigment more or less masking the green chlorophyll. 

 Many are unicellular, or consist of minute filaments, while 

 some of the so-called " seaweeds v are more elaborate in 

 structure, some possessing a root-like attachment organ and 

 with a floating thallus which may attain a length of 800 

 feet, or even more. 



114. Bacteria. This group in- Bacteria. 



eludes the smallest of all known plants. They are exceed- Account 

 ingly minute and of very simple structure, being unicellular 

 or filamentous, with no indications of any specialised tissue. 

 Many are always present in the air and soil, others live in 

 water, and others in dead or living organic matter. Many 

 are well known in connection with animal diseases and are 

 popularly spoken of as " germs," or " microbes." 



Regarding the size of bacteria, we may take, as a fairly 

 typical example, Bacterium aceti, the little individual rods of 

 which have a length and breadth of about ^ of an inch 

 and OQ of an inch, respectively. Many are capable of active 

 movement by means of exceedingly fine, hair-like processes 

 termed cilia or flagella. 



The presence or absence of these flagella and the shape of 

 the individual cells are important characters for the classi- 

 fication of bacteria. The following forms, for instance, are dis- 

 tinguished by the characters given : 



(a) Cocci, minute spherical cells. 



(b) Bacteria, rod-like cells with no flagella. 



(c) Bacilli, rod-like cells with flagella scattered over the 



whole surface of the cell. 



(d) Spirally curved forms (Vibrio closely wound, usually 



with one polar flagella, Spirillum closely wound 



