934 PRINCIPLES OF STRATIGRAPHY 



and may reach an expanse of several feet, though generally small. 



The Scliicophyta form a group distinct from the preceding and 

 unconnected with them or higher types. Bacteria are minute uni- 

 cellular plants, devoid of chlorophyll, and multiplying by repeated 

 division. In form they are spherical, oblong, or cylindrical, often 

 forming filamentous or other aggregates of cells. The absence 

 of an ordinary nucleus, of the ordinary sexual method of repro- 

 duction, and the manner of division, unite them with the Cyano- 

 pJiycecc, or blue-green algse. Some forms (Sarcina) show relation- 

 ship to, or analogies with, green algae (Palmcllacecr), while others 

 suggest relationship to myxomycetes. Again, certain features sug- 

 gest some flagellates and many forms exhibit a power of indepen- 

 dent movement when suspended in a fluid. The group is no doubt a 

 heterogeneous one, including at present primitive forms of many 

 types of plants. Their size is commonly I/a* in diameter and 

 from two to five times that length, though smaller and larger forms 

 are known. They occur fossil since Devonic and probably earlier 

 time. 



The Cyanophycccc are unicellular or multicellular and contain, 

 besides chlorophyll, a blue-green coloring matter, hence their name, 

 though the actual color of some ranges from yellows to browns, 

 reds, purples, or violets of all shades. Generally the single cells 

 are held together in a common jelly. Some members of this division 

 secrete lime ( Glueocapsa, Gkeothece) and serve to build up con- 

 siderable deposits (see organic oolites, Chapter XI). Nearly a 

 thousand species of Cyanophyce?e are known. No fossil representa- 

 tives are known, though they must have existed in earlier ages. 



Phylum II — TiiALLuriivxA. The vegetative portion of these 

 plants consists of one or many cells forming a thallus, often 

 branched. There is no dififerentiation of the body into a root, 

 stem, or leaf, while the internal structure is comparatively simple. 

 Both sexual and asexual reproduction take place. In many classi- 

 fications the Bacteria, the Cyanophycccc, and the Myxomycetes are 

 also classed here, and, besides them, the following classes are made : 

 I. Peridinecc, 2. Conjugatcc, 3. Diatoiiiacecc (Diatoms), 4. Hetcro- 

 contecc, 5. Chlorophycccc (Green algae), 6. Characece (Stoneworts ), 

 7. Rhodophycecc (Red algse), 8. Eumycetes (Fungi), 9. Phycomy- 

 cetes (Algal fungi), 10. Phccophycecc (Brown algae). The older di- 

 vision into the three classes of a, Algw, bearing Chlorophyll; b, 

 Fungi, without Chlorophyll; and c, Liclicns, symbiotic colonies of 

 algae and fungi, is the most familiar and will be used here. 



* One micromillimeter or 0.00 1 mm. 



