268 INTRODUCTION TO BOTANY 



It may grow about the edge of the water or upon extremely 

 wet soil that has been formed by the partial decay of plants. 

 On account of the peculiar structure of the leaves these plants 

 hold water in great quantities. The leafy shoot of Sphagnum 

 continues its growth at the tip from year to year, while the 

 older submerged portions gradually become partially decayed 

 and intermingled with other plant material. A semi-solid sur- 

 face of soil is gradually formed, and this often supports many 

 kinds of plants beside Sphagnum. After long periods of accu- 

 mulation the partially decayed material becomes compressed by 

 the increasing weight above it and is known as peat. When 

 removed and dried (sometimes compressed into bricks), it is 

 used as fuel and finds a market in many parts of the world. 

 Sphagnum is quite commonly used as a packing material and 

 also for holding moisture about potted plants. 



254. General characteristics of the liverworts. These pecul- 

 iar plants (fig. 206) take their name from their supposed 

 resemblance to the human liver. Most of them grow in moist, 

 well-shaded regions, though sometimes they are quite exposed 

 and in a few cases they may even grow in intense light and 

 heat. Few of them look much like mosses, but some have 

 leaf-like structures which quite closely resemble them. 



The most commonly found liverworts lie flat upon the 

 ground or upon whatever supports them. From the under- 

 surface many rhizoids grow. The plants are usually dark 

 green, being abundantly supplied with chlorophyll. They grow 

 forward, the lobes continuing to branch until solid mats are 

 formed. Older portions of v the plant die, leaving the younger 

 branches as new and independent plants. 



In some liverworts, cups form on the upper surface, and in 

 these cups small, flattish, green buds are developed. These 

 buds, when they fall from the cups or are removed in some 

 other way, may grow into new liverwort plants. Also, in such 

 liverworts as those shown on page 269, upright stalks grow 

 from the prostrate parts of the plants, and in the heads that 

 are produced on the ends of these stalks the sex organs are 



