128 



KINGDOMS MONERA AND PROTISTA: 



atmosphere, plus the replacement of these com- 

 pounds by oxygen, set the scene for the extinction of 

 many ancient organisms and the success of those 

 mutants that could survive within an oxygen medium. 

 In this earliest Actualistic Phase a small amount of 

 oxygen probably existed because lightning continu- 

 ally changed water vapor into its component parts of 

 hydrogen and oxygen. 



Present-day Monera, then, probably are a remnant 

 of life that dominated the past. However, this is not 

 meant to imply that living forms are "living fossils," 

 in the sense of existing some two or more billion 

 years. Rather, living Monera probably are the prod- 

 uct of eons of evolution. Many specialized types, 

 especially those closely adapted to relatively recent 

 geological conditions, show that the Monera have not 

 stood still since ancient times. On the other hand, 

 reference to the diagnoses of the two living phyla does 

 indicate how simple are most living monerans in 

 contrast to other living groups. Even a brief com- 

 parison of the bacteria and blue-green algae with the 

 protistans will show various differences. In such a 

 comparison, one must realize that the seemingly sim- 

 ple differences actually represent marked divergences 

 in microscopic structure. Before reading the rest of 

 this chapter, review the structures in cells (Figure 

 6.8, p. 92), the life cycles (Figures 6.4 through 6.7, pp. 

 89-91), and nutrition types (p. 85). 



SCHIZOPHYTA (Bacteria) 



Diagnosis: protoplasmic organization, cell-like 

 and mostly solitary but some are colonial; solitary 

 individuals are spherical (cocci), short rods or cylin- 

 ders (bacilli), or corkscrew-like (spirilla); colonial 

 forms are chain-like or hair-like (filamentous), but a 

 few have a definite terminal spore-producing struc- 

 ture (sporangium) similar to that of the slime molds 

 (Myxomycophyta); excluding the viruses, bacteria 

 are the smallest living creatures (Figure 8.1). 



Structure: nucleus simple, incompletely developed, 

 without complex internal structures and not de- 

 limited by a nuclear membrane; cytoplasm with 

 neither plastids, one or more central vacuoles 

 (structures present in most green flagellates and 

 algae), nor other complex structures that are found 

 in most plants (Figure 6.8); cytoplasmic pigments 

 present or absent, but probably not of the type pres- 

 ent in green flagellates and algae; chlorophyll present 

 in a special form (bacteriochlorophyll) and involved 



BACTERIA (mostly highly magnified) 

 COCCI types bacilli types spirella types 



flagellated types 



filamentous colony 



f i lament 



Figured.] Bacteria types. 



in photosynthesis (a particular type without the re- 

 lease of oxygen); only about one-third are pigmented 

 with bacteriochlorophyll or some other substance; 

 most have a cell wall; simple, thread-like locomotor 

 structures (flagellae) may be absent or one, two, or 

 several may be present. 



Nutrition: all types except holozoic are known. 



Reproduction: mostly asexual by cell division with- 

 out the segregation of chromosomes (amitotic); some 

 forms produce spores that are more resting cells than 

 true spores (a usually single-celled, asexually re- 

 producing structure); bacterial spores are formed and 

 persist in unfavorable environmental conditions; the 

 few complex bacteria form true reproductive spores 

 at the end of a hair-like filament or in a specialized 

 spore-producing sporangium; typical sexual repro- 

 duction with zygote formation does not occur, but 



