CHAPTER VIII 



NUTRITION IN THE LOWER PLANTS; 

 CHEMOSYNTHESIS 



Death rides in every passing breeze, 



He lurks in every flower, 

 Each season has its own disease, 



Its peril every hour. 



— R. Heber. 



The Fungi. — Although this book is primarily concerned with 

 the physiological problems of the higher plants, it has been deemed 

 excusable and profitable, either because of their great economic 

 importance or because of their interest from the viewpoint of 

 general physiology, to introduce here a chapter on the special 

 physiology of some of the Thallophytes, notably the fungi, which 

 contain no chlorophyll, and in the majority of cases must derive 

 their energy from organic compounds as described in the previous 

 chapter. They live either parasitically or saprophytically, the 

 same classification applying here as in the dependent seed plants. 

 Among the saprophytes are to be found three groups of outstand- 

 ing importance, — the yeasts, the molds, and the bacteria. 



The Saprophytes. — The yeasts are simple one-celled plants, 

 which grow especially well on sugars. They are found almost 

 universally in nature and are cultivated for their use in two im- 

 portant industries— brewing and baking. The sugars found in beer 

 wort, grape juice, and other fruit juices supply them with the 

 food necessary for their growth and rapid reproduction. They 

 will be discussed further in Chapter XXV. 



The molds are another group of saprophytic organisms. These 

 filamentous plants so common on fruits, vegetables, etc., are not 

 very exacting in their nutrition, but are able to use a wide variety 

 of organic food. Certain saprophytes are much more limited in 

 their nutritional requirements than others; some can grow and 

 thrive on only one kind of food while others can be grown prac- 

 tically anywhere. The members of the former group thus lend 

 themselves to the method of " selective culture" in isolation ex- 

 periments. 



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