CLASSIFICATION OF PLANTS. 



19 



movements. Others are so small as to appear as mere lines and dots, 

 even with the strongest lenses. Among the common forms are small, 

 nearly globular cells ; oblong, rod- 

 shaped or thread- shaped filaments, 

 either straight or curved, or even spi- 

 rally twisted. Frequently they show 

 a quick movement which is probably 

 in all cases due to cilia, which are, 

 however, too small to be seen in most 

 cases. 



Reproduction is for the most 

 part by simple transverse divis- 

 ion, as in oscillaria; but occa- 

 sionally spores are produced 

 also. 



FIG. 9. Euglena. A , individual in 

 the active condition. E, the red 

 " eye-spot." c, flagellum. n, nu- 

 cleus. B, resting stage. C', indi- 

 vidual dividing, x 300. 



CLASS III. GREEN MONADS ( Volvocinece) . 



This group of the protophytes is unquestionably closely re- 

 lated to certain low animals (Monads or Flagellata), with which 

 they are sometimes united. They are characterized by being 

 actively motile, and are either strictly unicellular, or the cells are 

 united by a gelatinous envelope into a colony of definite form. 



Of the first group, Euglena (Fig. 9), may be selected as a type. 



This organism is found frequently among other algse, and occasion- 

 ally forms a green film on stagnant water. It is sometimes regarded as 

 a plant, sometimes as an animal, and is an elongated, somewhat worm- 

 like cell without a definite cell wall, so that it can change its form to some 

 extent. The protoplasm contains oval masses, which are bright green in 

 color ; but the forward pointed end of the cell is colorless, and has a little 

 depression. At this end there is a long vibratile protoplasmic filament 

 (c), by means of which the cell moves. There is also to be seen near this 

 end a red speck (e) which is probably sensitive to light. A nucleus can 

 usually be seen if the cell is first killed with an iodine solution, which 

 often will render the flagellum (c) more evident, this being invisible while 

 the cell is in motion. The cells multiply by division. Previous to this 

 the flagellum is withdrawn, and a firm cell wall is formed about the cell 

 (F?g. 9, B). The contents then divide into two or more parts, which 

 afterwards escape as new individuals. 



