656 GEOLOGY, 



geyser basins of the Yellowstone Park/ and the diatom oozes of the deep 

 sea (Fig. 353, p. 425). 



Fungi, for obvious reasons, have left but scant traces of themselves. 



Bacteria are believed to be recognizable as far back as the Paleozoic 

 era. They are now the chief agents in the decomposition of organic 

 matter, and may be regarded as the prime enemies of the fossil record. 

 It is probable that similar decomposition took place actively in the 

 earliest ages, for otherwise the remains of the ancient organisms should 

 be more abundant. There is hence a theoretical probability that bac- 

 teria flourished as far back as the stratigraphic record goes. Not 

 unlikely they were originally simple algse that turned from the primi- 

 tive habit of making their own food, to living on other organisms or their 

 remains, and in so doing lost their power of manufacturing chlorophyl 

 and of using inorganic carbon compounds. Their remarkable adapta- 

 tion to the most varied conditions, and their extraordinary ability to 

 endure the greatest vicissitudes of environment, support the view that 

 they are a very ancient and plastic form. 



At present certain bacteria are important to higher vegetation 

 because of their ability to use the free nitrogen of the atmosphere and 

 to combine it into forms available for the higher plants. It is not 

 improbable that they have subserved this important function through 

 all the known ages. Some experiments seem to show that certain of 

 the existing algse have this power, and possibly the ancestral forms of 

 plants possessed it. The bacteria, being a derived and not an original 

 form, could not have performed the function for the first plants. It is 

 possible, of course, that the inorganic supply of nitrogen compounds 

 was sufficient for plant life at the outset. 



The contribution of the Bryophytes (liverworts, mosses) . — The 

 mosses and liverworts have left no certain record of their work in the 

 earlier and middle geologic eras, and, if they existed at all, their con- 

 tributions were unimportant. Although low forms of plant life, they 

 are not primitive ones, as they are characterized by a definite alterna- 

 I'cn cf g?:icrat-ons implying a considerable time antecedent to the 

 attainment of Ihclr' present forms; hence there are no very cogent 

 theoretical reasons for assigning them a place in early geologic history, 

 though their absence cannot be affirmed. Some botanists think the 

 ^'teridophytes were derived from some ancestral form of hverwort, 

 1 Weed. Ninth Ann. Rept. U. S. Geol. Surv., 1887-8. 



