122 PLANTS, THE FOOD OF ANIMALS 



ful cycle of matter and energy in nature whereby living things 

 are all interrelated and balanced. Plants manufacture pro- 

 teins which are built up into animal protoplasm. Plants also 

 produce glucose which, acted upon by yeast, is transformed into 

 alcohol and CO2. The alcohol is acted upon by bacteria and 

 changed to acetic acid and water, other bacteria act upon this 

 acetic acid and change it to CO 2 and water. Plants and ani- 

 mals die, their protoplasm, as protein, is acted upon by bacteria 

 and broken down into free ammonia, nitrites, nitrates, sulphates, 

 phosphates and other salts, all of which are returned to the earth 

 to be taken up by the roots of plants and built again into plant 

 protoplasm. Animals, and to a less extent, plants, produce 

 nitrogenous waste as a product of metabolism. This is acted 

 upon by bacteria and turned into NHs and CO2 and water. 

 In this way there is a continual cycle of simple salts and gases 

 converted into starches, sugars, plant and animal protein with 

 high potential energy which is ultimately transformed into 

 energy of heat, light, electricity and movement, giving the 

 infinite variety of vital manifestations. This protein, through 

 oxidizing agents and nitrifying agents, is finally brought again to 

 the state of elementary compounds. All may be shown in 

 a simple diagram (Fig. 48) . 



REPRODUCTION OF THE FERN 



The rhizome of the fern may give rise now and then to branch 

 rhizomes which start up independent plant growths, and thus 

 bring about a form of reproduction somewhat analogous to 

 budding in Hydra. This, however, is only an exceptional 

 method of reproduction and does not amount to much in the 

 distribution of the fern. The chief methods of reproduction 

 do not involve the rhizome at all, but take place as a result of 

 activity of the frond cells. As in hydroids, reproduction here 

 involves an alternation of generations, sexual and asexual 

 generations following each other in regular succession. 



The Asexual Generation (Sporophyte). The ordinary fern 

 plant is the asexual generation, i.e., it does not form the sex cells 



