DECAY 177 



or even by slight movements of the air ; their extreme buoy- 

 ancy keeps them afloat for prolonged periods, though they 

 eventually settle as one of the ordinary constituents of dust ; 

 they offer a high degree of resistance to deleterious influences, 

 and are thus capable of bridging over critical periods, at the end 

 of which they may germinate with great freedom. It will thus 

 be seen that through such spores it is possible for the fungi to 

 develop wherever and whenever favorable conditions are met 

 with. The life history of the fungi is usually much longer and 

 more complex than that of the bacteria, and while the life cycle 

 often involves both a sexual and an asexual phase, the former 

 may not appear throughout a very much prolonged period of 

 development, within which the plant may nevertheless extend 

 with great rapidity and produce all the characteristic effects 

 of its growth. 



Both the bacteria and the fungi are characterized by the ab- 

 sence of a green pigment, or chlorophyll, and their consequent 

 inability to produce carbon compounds from the carbon dioxide 

 of the atmosphere as a source of energy. With the exception of 

 a few of the bacteria, the energy of all these plants depends 

 entirely upon the oxidation of carbon compounds previously 

 formed and accumulated by some other organisms, primarily 

 those which contain chlorophyll. It is therefore imperative that 

 such compounds should be derived directly from the nutrient 

 fluids of a living organism, or /tost, upon which the parasite 

 feeds ; or that it should be obtained as one of the products of a 

 decay induced by the fungus or bacillus which thereby becomes 

 a saprophyte. From the nature of their process of nutrition, 

 saprophytes are generally found within the body upon which 

 they act, and they are thus endophytic. This is particularly 

 true of the bacteria. The more highly organized fungi may 

 live chiefly upon the surface of the body (epiphytic), sending 

 the branches of their mycelium (the hypha) into the interior 

 parts, where they develop specialized feeding branches (Jiaus- 

 toria), which arise wherever food supplies are to be met with. 

 Or, again, endophytic forms may reach the surface only at certain 



