12 MANUAL OF ANIMAL BIOLOGY 



also numerous, small spherical bodies, the pyrenoids, which func- 

 tion in the formation and storage of reserve starch. (B. p. 21.) 

 Elodea. This is a highly developed, water-living species belong- 

 ing to the Flowering Plants. In a plant of this type the cells are 

 specialized for various functions. The chlorophyll-bearing cells 

 are largely centered in the leaves, which are to be regarded as 

 highly specialized organs for the processes associated with food 

 manufacture. The chloroplastids of Elodea are tiny disc-shaped 

 bodies which lie embedded in the cytoplasm near the cell wall. 

 The cytoplasm of Elodea exhibits a noteworthy flowing movement, 

 which is considered later (p. 16), and the chloroplastids are carried 

 along in the current. 



Colorless Plants. It has been noted above that the Colorless 

 Plants, or Fungi, which include a large number of species belonging 

 to such well-known groups as the Bacteria, Yeasts, and Molds, 

 are characterized by the absence of chlorophyll. They are unable, 

 therefore, to satisfy their nutritive requirements through the syn- 

 thesis of essential foodstuffs from the inorganic materials in their 

 environment as are the Green Plants. The Fungi, like the animals, 

 must have organic compounds which had their origin in photosyn- 

 thesis. On the other hand there is a wide divergence in their 

 nutritive requirements, and many fungus species find adequate 

 food materials in compounds much less complex in their chemical 

 nature than those required for animal nutrition. Because of this, 

 the Fungi play an essential role in the cycle of elements in nature 

 by utilizing various organic substances which are not suitable for 

 the nutrition of either green plants or of animals. In such cases 

 the constituent elements can then be again utilized in photosyn- 

 thesis by the chlorophyll-bearing plants. Furthermore, the Fungi, 

 in their quest for nutrients, attack the tissues of dead organisms — 

 the process of decay — and in the end make available to the 

 green plants the vast amounts of materials there present which 

 would otherwise be lost. Three groups of Fungi may now be in- 

 dicated. (W. pp. 37-45.) 



Bacteria. There are some 1400 species of Bacteria known, all of 

 which are microscopic in size, and, in addition, there are undoubtedly 

 many other species which are too small to be seen even under the 

 highest magnification of the microscope. Structurally the bacteria 

 cell appears to be very simple, consisting of a bit of cytoplasm, 

 in which a definite nucleus is not apparent, enclosed in a cell wall. 



