10 



PLANT LIFE. 



over the gelatinous part of the wall is much less prominent, 

 so that often it is only seen with difficulty. Even though 

 invisible, it may be detected by the slippery feel of the 

 plants when rubbed gently between the fingers. 



' ^~^TJ^* i "?"- : " ' ' " '' 



FIG. 14. 



FIG. 15. 



FIG. 14. Part of a filament of Anabcena. /i, heterocyst; a-d, successive stages in 

 the division of a cell of the filament. Magnified 540 diam. After Strasburger. 



FIG. 15. Oscillaria. a, the tip; b, a portion of the middle of a filament. Magnified 

 540 diam. After Strasburger. 



15. Feeding habits. --The feeding habits of the oscil- 

 larias are worth notice. They are found in permanent 

 puddles and ditches where organic matter is decaying. The 

 significance of this is that some of the ancestors of the green 

 oscillarias probably had offspring which, instead of living 

 upon food prepared by means of the green coloring matter 

 (see \ 230), learned to utilize the organic matter in the 

 water, at first perhaps no more than the present oscillarias 

 do ; but gradually they came to live exclusively upon it. 

 As a consequence, they lost their color and became incapable 

 of existing where organic food cannot be had. 



Bacteria. 



16. Fission-fungi. Along with the loss of color and 

 change of habit went a diminution in size. They have thus 



