CYCLE OF MATTER AND ENERGY 119 



which are built up into animal protoplasm. Plants also produce 

 glucose which, acted upon by yeast is transformed into alcohol 

 and CO 2 . 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 animals die, 

 their protoplasm as proteid is acted upon by bacteria and broken 

 down into free ammonia, nitrites, nitrates, sulphates, phos- 

 phates 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 CO 2 and water. 

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

 converted into starches, sugars, plant and animal proteid with 

 high potential energy which, used as food and ultimately trans- 

 formed into energy of movement, gives the infinite variety of 

 movement and other vital manifestations. This proteid 

 through oxidizing agents and nitrifying agents is finally brought 

 again to the state of simple 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. The ordinary fern plant is the 

 asexual generation, i.e., it does not form the sex cells but, like 

 the hydroid, it gives rise without fertilization to an organism 

 different from .itself. These dissimilar organisms are formed 



