44 AN INTRODUCTION TO THE STUDY OF FOSSILS 



stage, — the product of the union of male and female elements, 

 and the sexiial or gametophyte stage, — the product of the ger- 

 mination of the spores. 



The moss plant is distinguished b\' the predominance of the 

 gametophyte stage over the sporophyte, since the sporophyte 

 is only the slender stalk and its capsule, dependent on the leafy 

 moss plant, — the gametophyte. 



Derivation of name. — Greek bryoii, moss, + pliyfou, plant, 

 referring to its typical class, the mosses. 



The Bryoph\'ta are divided into two classes, — the liverworts 

 (Hepaticte) and the mosses (Musci). 



Liverworts include the simplest br^'ophytes, with many 

 similarities to the Algie. IVIarchanlia is a connnon example 

 (Fig. II, B). 



A common moss is the hair-cap, Polyly'ichum commune (Fig. 

 II, C). JNIosses, especially of the genus Sphagnum, have been 

 in recent times most important agents in the formation of peat. 

 Such mosses grow in bogs, and as they die below continue to 

 grow above. They are mainl\- sub-arctic to cold temperate 

 in habitat. The Dismal Swamp sphagnum is one of the most 

 southerly deposits, occurring thirty-five feet thick. 



There is no fossil record of mosses and liverworts earlier 

 than the Tertiary, though probably they are not confined to 

 such relatively modern times. 



1. Describe both stages (gametophyte and sporophyte) of 

 a common moss plant. 



2. Give two dift"erences between a thallophyte and a bryo- 

 phyte. 



3. How far back in geologic time are fossil mosses found ? 



4. Name the two classes into which the Bryophyta are divided, 

 with an example under each. 



DIVISION III. PTERIDOPHYTA 



The pteridophytes are much more complex plants than the 

 bryophytes. While the structure of the moss plant is more or 

 less simply cellular, that of the fern plant is vascular ; that is, 



