250 Plant Biology 



Fossil diatoms form "diatomaceous earth" which forms the basis of 

 many scouring or cleaning materials, such as metal polishers and tooth 

 pastes. Certain diatoms, because of their fine, regular markings, are 

 used as test objects for calibrating microscope lenses. Diatomaceous 

 earth is also used as a heat-insulating material. It may also be molded 

 into hollow cylinders or "bougies" used in making bacteriologic filters. 

 Dynamite is made by absorbing nitroglycerin in diatomaceous earth. 



II. ECONOMIC IMPORTANCE OF FUNGI (Figs. 34 to 42) 



Fungi by their growth in foods, clothing, and lumber frequently de- 

 stroy them or diminish their values. One of the principal wood-rotting 

 fungi (Merulius lacrymans) attacks wood at rather low temperatures, 

 about 15° C. These fungi do not thrive in water or water-logged soils 

 because they are aerobic. Decay of wood thus occurs most rapidly near 

 the ground- or water-line. Heartwoods are generally more resistant than 

 sapwoods. Certain fungi, including bacteria, help in the necessary and 

 desirable decay of plant and animal remains, thus removing them from 

 the water and soil and rendering their constituents again available for 

 use by future living organisms. 



Certain types of mushrooms (class Basidiomycetes) are used as human 

 foods. Several species are extremely poisonous and cause severe illness 

 or death when eaten. Great care should be taken in the selection and 

 use of mushrooms. Unless the collector is absolutely certain the species 

 is nonpoisonous, he should discard it. In case of doubt, the specimens 

 in question should be discarded. The flavors which are characteristic of 

 certain cheeses are produced by specific fungi. The characteristic odors 

 and tastes of Roquefort cheese and Camembert cheese are produced by 

 the molds Penicillium roqueforti and Penicillium camemherti, respec- 

 tively (Fig. 39). 



Penicillium notatum, Aspergillus sp. (Fig. 73), and numerous other 

 fungi produce penicillin and other antibiotic substances successfully used 

 in the treatment of many diseases. Recent discovery of the remarkable 

 curative values of penicillin and other antibiotic substances has stimu- 

 lated great interest in the entire field of chemotherapy. In 1877, Pasteur 

 and Joubert discovered that certain airborne organisms inhibited the 

 growth of anthrax bacilli, and they suggested that antibiotics might be 

 utilized in the treatment of certain infections. Dr. Alexander Fleming 

 in London (1929), observing a plate culture of Staphylococcus organ- 



